WO2016002227A1 - Liquid fuel cell partitioning membrane and membrane-electrode-assembly provided with same - Google Patents

Liquid fuel cell partitioning membrane and membrane-electrode-assembly provided with same Download PDF

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Publication number
WO2016002227A1
WO2016002227A1 PCT/JP2015/003348 JP2015003348W WO2016002227A1 WO 2016002227 A1 WO2016002227 A1 WO 2016002227A1 JP 2015003348 W JP2015003348 W JP 2015003348W WO 2016002227 A1 WO2016002227 A1 WO 2016002227A1
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WIPO (PCT)
Prior art keywords
diaphragm
liquid fuel
water
fuel cell
weight
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PCT/JP2015/003348
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French (fr)
Japanese (ja)
Inventor
康壮 松田
武史 仲野
西井　弘行
Original Assignee
日東電工株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from JP2014137789A external-priority patent/JP2016015284A/en
Priority claimed from JP2014137790A external-priority patent/JP2016015285A/en
Priority claimed from JP2014137792A external-priority patent/JP2016015287A/en
Priority claimed from JP2014137791A external-priority patent/JP2016015286A/en
Application filed by 日東電工株式会社 filed Critical 日東電工株式会社
Publication of WO2016002227A1 publication Critical patent/WO2016002227A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/08—Fuel cells with aqueous electrolytes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/22—Fuel cells in which the fuel is based on materials comprising carbon or oxygen or hydrogen and other elements; Fuel cells in which the fuel is based on materials comprising only elements other than carbon, oxygen or hydrogen
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the present invention relates to a diaphragm for a liquid fuel cell and a membrane-electrode assembly including the same.
  • the polymer electrolyte fuel cell has advantages such as being able to operate at a low temperature as a fuel cell and having a high output density, and is expected to spread in the future.
  • the PEFC includes a diaphragm between the anode and the cathode, and a polymer electrolyte membrane having ion conductivity is used as the diaphragm. As this diaphragm, a cation exchange membrane has been used.
  • PEFCs using an anion exchange membrane that can generate electricity without using platinum as a catalyst have been reported (for example, Patent Document 1 and Patent Document 2).
  • the liquid fuel cell diaphragm is used by impregnating the diaphragm with an aqueous solution. Therefore, the diaphragm for liquid fuel cells is required to have a small area expansion before and after impregnation with the aqueous solution in order to prevent deformation when the aqueous solution is impregnated.
  • the pH of the aqueous solution contained in the diaphragm becomes acidic or alkaline.
  • a liquid fuel cell hereinafter referred to as an alkaline liquid fuel cell
  • the pH of the aqueous solution becomes alkaline. Accordingly, the diaphragm is required to have good chemical durability against the pH of the aqueous solution.
  • the present invention relates to a diaphragm for a liquid fuel cell, and an object thereof is to provide a diaphragm for a liquid fuel cell having a small area swelling rate and good chemical durability.
  • ion-exchange membranes are used as diaphragms for fuel cells, and these membranes are non-porous membranes.
  • a polymer porous membrane having a hydrophilic functional group by using a polymer porous membrane having a hydrophilic functional group, a membrane for a liquid fuel cell having a small area swelling rate and good chemical durability.
  • the present invention A diaphragm for a liquid fuel cell, A polymer porous membrane, Graft chains introduced into the polymer porous membrane; With The graft chain includes a hydrophilic functional group; A diaphragm for a liquid fuel cell is provided.
  • the present invention provides: There is provided a membrane-electrode assembly (MEA) comprising a diaphragm for a liquid fuel cell of the present invention.
  • MEA membrane-electrode assembly
  • the present invention it is possible to provide a diaphragm for a liquid fuel cell having a small area swelling rate and high chemical durability. According to the present invention, an MEA that takes advantage of the characteristics of the diaphragm can be obtained.
  • FIG. 3 is a longitudinal sectional view of a schematic evaluation cell on the III-III plane of FIG. 2. It is a front view which shows typically the cell for evaluation used for a water transmission rate test or a pressure resistance test.
  • liquid fuel cell diaphragm of the present invention is not limited to this and can be used for an acid liquid fuel cell. .
  • the MEA of this embodiment is suitable for use in a liquid fuel cell.
  • This liquid fuel cell is not particularly limited to a portion other than the MEA, and a known member can be applied.
  • the liquid fuel cell described below is an alkaline liquid fuel cell equipped with the MEA of the present embodiment, and liquid fuel is supplied to the anode side and oxidant is supplied to the cathode side.
  • the oxidizing agent is air, for example.
  • the liquid fuel is a fuel dissolved in water and dissolves an electrolyte.
  • the fuel is not particularly limited as long as it can be dissolved in water. Examples thereof include lower alcohols such as methanol and ethanol, amines such as hydrazine (hydrate) and ammonia, sodium borohydride, and the like. Hydrazine (hydrate) is preferable because it is high and does not generate CO 2 on the principle of power generation.
  • the amount of fuel supplied can be controlled by the concentration of fuel in the liquid fuel and the supply speed (flow rate).
  • the amount of fuel required varies depending on the amount of current to be extracted. Therefore, it is preferable to control the amount of fuel supplied to the anode side in accordance with the amount of current to be extracted. If an excessive amount of fuel is supplied relative to the amount of current to be extracted, the amount of fuel permeation may increase.
  • the permeated fuel is present on the cathode, more specifically, on the cathode catalyst, the oxidant and the fuel may directly react on the cathode catalyst to cause a side reaction, thereby reducing the power generation efficiency of the fuel cell.
  • a fuel providing system capable of controlling the supply amount of liquid fuel may be used.
  • the electrolyte is not particularly limited as long as it is an electrolyte that can be dissolved in water or liquid fuel and functions as an ionic conductor in the liquid fuel cell reaction.
  • an anion functions as an ionic conductor, so use an electrolyte that can dissociate hydroxide ions (OH - ions) such as potassium hydroxide, sodium hydroxide, and calcium hydroxide.
  • hydroxide ions OH - ions
  • potassium hydroxide which is a reaction product with carbon dioxide, is easily dissolved in water and hardly precipitated
  • potassium hydroxide is particularly preferable as the electrolyte.
  • other inorganic salts, ionic liquids, etc. that can be dissolved in water and can supply ions when dissolved in water can also be used as the electrolyte.
  • the concentration of the electrolyte in the liquid fuel is not particularly limited, but is, for example, 0.5 to 40%, particularly 1 to 20% on a weight basis.
  • the feature of the present embodiment is that the electrolyte bears ionic conductivity, and this point is different from the generally used liquid fuel cell.
  • an anion exchange membrane is used for the diaphragm, and the anion exchange group of the anion exchange membrane bears ion conductivity. Therefore, when the anion exchange group is deteriorated, the performance of the liquid fuel cell is lowered.
  • the MEA of the present embodiment that can conduct ions even without an anion exchange group, it is not necessary to consider the deterioration of the anion exchange group.
  • the diaphragm for a liquid fuel cell provided in the MEA of this embodiment has a hydrophilic functional group and can hold water in the diaphragm. Since the liquid fuel is supplied from the anode side to the MEA of this embodiment, water contained in the liquid fuel permeates the diaphragm to the cathode side and is used for the reaction in the cathode catalyst. Therefore, use of the MEA of this embodiment makes it possible to omit auxiliary equipment for humidification, which is advantageous in reducing the size of the liquid fuel cell and improving the power generation capacity per unit volume.
  • the above liquid fuel cell It is also possible to provide auxiliary equipment for processing the gas discharged from the outlet.
  • a catalyst layer is disposed on the surface of the diaphragm of the present invention.
  • the diaphragm and the catalyst layer are typically integrated through a processing step such as spray application of catalyst ink.
  • the catalyst layer includes an anode catalyst layer and a cathode catalyst layer.
  • FIG. 1 shows an example of the MEA of this embodiment.
  • the MEA shown in FIG. 1 includes a diaphragm 2, an anode catalyst layer 3, and a cathode catalyst layer 4.
  • the anode catalyst layer 3 is on one main surface of the diaphragm
  • the cathode catalyst layer 4 is on the other main surface of the diaphragm 2, respectively. Has been placed.
  • the method for forming the MEA is not particularly limited as long as the effects of the present invention are not impaired.
  • the CCM Catalyst Coated on Membrane
  • the CCS Catalyst Coated on Substrate
  • a catalyst layer provided in a known MEA used in an alkaline liquid fuel cell can be used. Unlike an acid fuel cell, the catalyst does not necessarily need to be a noble metal such as platinum. For example, a base metal such as nickel, cobalt, or iron can be used.
  • the structure of the catalyst layer, such as the specific catalyst contained, may be different or the same on the anode side (anode catalyst layer) and cathode side (cathode catalyst layer) of the MEA.
  • the cathode catalyst layer it is desirable to select a catalyst that selectively promotes the oxidation-reduction reaction from the viewpoint of suppressing a reaction with the permeated fuel to prevent a decrease in power generation efficiency and preventing member deterioration due to a side reaction.
  • the MEA of the present embodiment can have any member other than the diaphragm and the catalyst layer as long as the effects of the present invention are not impaired.
  • the diaphragm for a liquid fuel cell includes a polymer porous membrane and a graft chain introduced into the polymer porous membrane, and the graft chain includes a hydrophilic functional group.
  • the liquid fuel cell membrane preferably has a thickness in the range of 5 ⁇ m to 130 ⁇ m, and more preferably in the range of 10 ⁇ m to 70 ⁇ m. If the film thickness becomes too thin, the film strength may decrease, and the film may be damaged or defects such as pinholes may occur, which may prevent the pressure of the oxidizing agent from being maintained. Further, the amount of fuel permeation and the amount of water permeation (water permeation amount) may increase. If the film thickness becomes too thick, the resistance (film resistance) as a film within the diaphragm may increase, and the water permeability may decrease. When the amount of water permeation decreases, water required for the reaction in the cathode catalyst may be insufficient, and power generation efficiency may be reduced.
  • the water content of the diaphragm of the present embodiment is preferably 30% or more, preferably 40% to 100%, more preferably 50% to 80% with respect to the weight of the diaphragm at the time of drying.
  • the hydrophilic functional group of the diaphragm retains water, so that the pores of the porous film are compensated.
  • the pressure of an oxidizing agent such as Moreover, since the water retained in the diaphragm permeates to the cathode side, water can be efficiently supplied to the cathode catalyst, which can contribute to the improvement of the power generation efficiency of the battery. If the moisture content is too small, the pores of the porous membrane may not be sufficiently filled and may not be able to withstand the pressure of an oxidizing agent such as air. If the water content is too high, the pressure resistance of the diaphragm against a gas such as air may be reduced, and the pressure of the oxidant may not be maintained.
  • the diaphragm at the time of drying is a diaphragm in a state in which dimensional change does not occur after being left in an atmosphere of 23 ° C. and 50% relative humidity for 24 hours or more. It is a diaphragm in a state of being swollen by being immersed in water at 2 ° C. for 2 hours.
  • the moisture content can be measured using the following method.
  • a sample cut into a rectangular shape having a length of 30 mm and a width of 20 mm is left in an atmosphere at 23 ° C. and a relative humidity of 50% for 24 hours or more, and the weight of the sample in which no dimensional change occurs is measured (weight before water inclusion).
  • a weight is measured (weight after water-containing).
  • the weight after moisture is measured after wiping off excess water adhering to the sample surface with a filter paper or the like.
  • the moisture content is a ratio calculated based on the following formula.
  • Moisture content (%) ((weight after hydration) ⁇ (weight before hydration)) ⁇ 100 / (weight before hydration)
  • the diaphragm of this embodiment has a reduced area swelling rate and good dimensional stability.
  • the area swelling ratio is preferably less than 20%, more preferably 15% or less, further preferably 0% to 10%, and particularly preferably 0% to 5%. If the area swelling rate becomes too large, the diaphragm may be deformed, leading to deterioration of the diaphragm. Moreover, when the area swelling rate becomes too large, in the liquid fuel cell provided with the diaphragm of the present embodiment, the bondability between the diaphragm and the electrode during operation of the fuel cell may be inferior.
  • the area swelling rate can be measured using the following method.
  • a sample cut into a rectangular shape having a length of 30 mm and a width of 20 mm is left in an atmosphere of 23 ° C. and 50% relative humidity for 24 hours or more, and the area of the sample in which no dimensional change occurs is measured (area before water inclusion). Then, after immersing this sample in 30 degreeC pure water for 2 hours, an area is measured (area after water inclusion).
  • the area swelling rate is a ratio calculated based on the following formula.
  • Area swelling rate (%) ((area after water inclusion) ⁇ (area before water inclusion)) ⁇ 100 / (area before water inclusion)
  • a liquid fuel cell (alkaline liquid fuel cell) utilizing the movement of anions
  • fuel is supplied to the anode side and an oxidant such as air is supplied to the cathode side.
  • an oxidant such as air
  • this water is supplied by being humidified from the outside using an auxiliary device such as a humidifier.
  • auxiliary equipment it is desirable to omit auxiliary equipment as much as possible from the viewpoint of miniaturization of the fuel cell and improvement of power generation capacity per unit volume.
  • a liquid fuel cell Like a fuel cell using gas as a fuel, a liquid fuel cell includes a membrane-electrode assembly (MEA) in which a diaphragm and a catalyst layer are integrated. From the viewpoint of the stable power generation efficiency of the liquid fuel cell, it is required that separation at the interface between the diaphragm and the catalyst layer hardly occurs. Since deformation of the diaphragm at the interface with the catalyst layer can contribute to this separation, the diaphragm is required to have good dimensional stability.
  • MEA membrane-electrode assembly
  • the present inventors examined a diaphragm that can supply water to the cathode side satisfactorily. As a result, it was found that water can be stably supplied to the cathode side by using a diaphragm having a moisture content of a specific value or more.
  • the diaphragm in order to suppress the separation between the diaphragm and the catalyst layer in the MEA, the diaphragm has a good dimensional stability, particularly, has a good dimensional stability at the interface between the diaphragm and the catalyst layer (area direction of the diaphragm). It is preferable. As a result of studies by the present inventors, it has been found that the separation of the membrane and the catalyst layer in the MEA can be suppressed by using a membrane having an area swelling ratio in a specific range.
  • the ratio of the weight difference between the weight of the diaphragm when wet and the weight of the diaphragm when dried to the weight of the diaphragm when dried is 30% by weight or more, The ratio of the area difference between the area of the diaphragm when wet and the area of the diaphragm when dried to the area of the diaphragm when dried is less than 20%.
  • a diaphragm for a liquid fuel cell is provided.
  • the liquid fuel cell is preferably in alkaline form.
  • the present invention can provide a diaphragm for a liquid fuel cell that can contribute to improving the characteristics of the liquid fuel cell.
  • a dry diaphragm swells when it absorbs water. Therefore, it has been difficult to obtain a diaphragm having both a good moisture content and a good dimensional stability (suppressed swelling rate). On the other hand, the moisture content of the diaphragm is good, and swelling in the area direction of the diaphragm is suppressed.
  • This diaphragm is preferably a porous film having a hydrophilic functional group.
  • the diaphragm preferably comprises a porous membrane and a hydrophilic functional group present on the porous membrane.
  • the porous film include a porous film made of an inorganic base material and a porous film made of a polymer base material.
  • the water transmission rate in the cross-sectional direction is preferably 40 mol / h ⁇ g or more, more preferably 40 to 120 mol / h ⁇ g, and more preferably 50 to 110 mol / h ⁇ g. Further preferred. If the water permeation rate in the cross-sectional direction of the diaphragm becomes too small, water necessary for the reaction on the cathode catalyst may not permeate sufficiently, and the reaction efficiency in the cathode catalyst may be reduced.
  • the diaphragm of the present embodiment in which the water permeation speed in the cross-sectional direction is in a specific range, water that has permeated the diaphragm from the anode side to the cathode side can be appropriately supplied to the cathode catalyst.
  • the reaction efficiency on the cathode catalyst can be improved, and the power generation efficiency of the battery can be further improved.
  • the water transmission rate in the cross-sectional direction of the diaphragm can be measured by the following method using the evaluation cell 100 shown in FIGS.
  • a diaphragm 2 having a first main surface and a second main surface opposite to the first main surface is prepared, and a diaphragm is formed by a pair of gaskets 11 and 21 having square openings 11a and 21a each having a side length of 2 cm. 2 is pinched.
  • a pair of separators 12 and 22 with serpentine-structured flow channels 12a and 22a, a pair of current collector plates 13 and 23, and a pair of end plates 14 and 24 are arranged in this order to form the diaphragm 2 Hold it.
  • Each member is fastened using a fixing part (not shown) such as a bolt so that air and water do not leak from each contact surface of the member, and the evaluation cell 100 is formed.
  • the evaluation cell 100 has flow paths 18, 19, 28, and 29.
  • the channels 18 and 19 are channels for supplying and discharging water, respectively, and the channels 28 and 29 are channels for supplying and discharging dry air, respectively.
  • Each flow path 18, 19, 28, 29 has an opening in the end plate.
  • the flow paths 18 and 19 penetrate the end plate 14, the current collector plate 13, and the separator 12, and are connected to the flow path 12a.
  • the evaluation cell 100 is installed so that the first main surface and the second main surface of the diaphragm 2 are along the vertical direction, and supply of water and dry air to the evaluation cell 100 in this state is started. 2 ml of water per minute is supplied to the first main surface via a pipe 38 connected to the flow path 18, and 500 ml of dry air per minute is supplied to the second main face via a pipe 48 connected to the flow path 28. Supply. By continuing to supply water as described above, the inside of the first main surface side of the cell 100 is filled with the supplied water, and the first main surface of the diaphragm 2 is always in contact with water.
  • the evaluation cell 100 is heated using the rubber heaters 15 and 25 provided on the end plates 14 and 24 so that the temperature of the evaluation cell 100 becomes 80 ° C.
  • Water and dry air are continuously supplied as described above, and water discharged from the pipe 39 connected to the flow path 19 is collected for 30 minutes while maintaining the temperature of the evaluation cell 100 at 80 ° C. (W2).
  • W1 is the weight of water supplied to the evaluation cell 100 for 30 minutes
  • W2 is the weight of water recovered from the pipe 39 for 30 minutes
  • W3 is the W3 measuring diaphragm of the same type and the membrane 2 was prepared separately from the diaphragm 2, were calculated from the weight measured 24 hours Hosei after standing in an atmosphere 23 ° C. relative humidity 55%, 1 cm of the membrane 2 It is per weight.
  • the water transmission rate in the cross-sectional direction of the diaphragm is a value calculated by the following formula using these values.
  • the pressure resistance between the main surfaces of the diaphragm is preferably 60 kPa or more, more preferably 80 kPa or more, and further preferably 100 kPa or more.
  • the pressure resistance between the main surfaces of the diaphragm is the maximum value of the pressure between the main surfaces that can maintain the diaphragm. If the pressure resistance between the main surfaces of the diaphragm is too small, the pressure of the oxidizing agent that is a gas may not be maintained, and the oxidizing agent may leak to the anode. If the oxidant leaks to the anode and the fuel and the oxidant are mixed directly, the power generation efficiency may be reduced.
  • the pressure resistance between the main surfaces of the diaphragm can be measured by the following method using the evaluation cell 100 shown in FIGS.
  • This evaluation cell 100 is formed in the same manner as the evaluation cell 100 used for the measurement of the water transmission rate in the cross-sectional direction of the diaphragm described above.
  • the evaluation cell 100 is installed so that the first main surface and the second main surface of the diaphragm 2 are along the vertical direction, and supply of water and dry air to the evaluation cell 100 in this state is started. 2 ml of water per minute is supplied to the first main surface via a pipe 38 connected to the flow path 18, and 500 ml of dry air per minute is supplied to the second main face via a pipe 48 connected to the flow path 28. Supply. By continuing to supply water as described above, the inside of the first main surface side of the cell 100 is filled with the supplied water, and the first main surface of the diaphragm 2 is always in contact with water. At this time, the evaluation cell 100 is heated using the rubber heaters 15 and 25 provided on the end plates 14 and 24 so that the temperature of the evaluation cell 100 becomes 80 ° C.
  • the pressure adjusting device 43 (for example, a valve) provided in the pipe 49 connected to the flow path 29 while maintaining the temperature of the evaluation cell 100 at 80 ° C. while continuing to supply water and dry air as described above. And the pressure of the dry air to the second main surface is increased so that the pressure of the dry air to the second main surface of the diaphragm 2 is 20 kPa. The pressure of the dry air is measured with a pressure gauge 42 provided in the pipe 49. Thereafter, the pressure regulator 43 continues to supply water and dry air as described above, and maintains the temperature of the evaluation cell 100 at 80 ° C. so that the pressure of the dry air to the second main surface can be maintained at 20 kPa. Adjust the opening.
  • a valve for example, a valve
  • the pressure of the dry air to the second main surface is measured for 10 minutes while maintaining the supply rate of water and dry air, the temperature of the evaluation cell 100, and the opening degree of the pressure adjusting device 43.
  • the withstand pressure between the main surfaces of the diaphragm is evaluated as 0 kPa.
  • the pressure of the dry air to the second main surface is increased, and the same measurement is performed in the order of 40 kPa, 60 kPa, 80 kPa, and 100 kPa.
  • the pressure resistance between the main surfaces of the diaphragm is set to 100 kPa.
  • the case where the pressure can be maintained means that the change in the pressure of the dry air to the second main surface is 1 kPa or less in 10 minutes.
  • a liquid fuel cell (alkaline liquid fuel cell) utilizing the movement of anions
  • fuel is supplied to the anode side and an oxidant such as air is supplied to the cathode side.
  • the reaction on the cathode side requires water in addition to the oxidizing agent.
  • this water is supplied by being humidified from the outside using an auxiliary device such as a humidifier.
  • auxiliary equipment it is desirable to omit auxiliary equipment as much as possible from the viewpoint of miniaturization of the fuel cell and improvement of power generation capacity per unit volume.
  • the diaphragm is also required to have a function of separating the oxidant and the fuel. Since a gas such as air is used as the oxidizing agent, the diaphragm needs to have good pressure resistance against the gas.
  • the water transmission rate in the cross-sectional direction is 40 mol / h ⁇ g or more, And while supplying water to the first main surface, air is supplied to the second main surface opposite to the first main surface and the pressure between the main surfaces measured by increasing the pressure of the air is 80 kPa or more. is there, A diaphragm for a liquid fuel cell is provided.
  • the liquid fuel cell is preferably in alkaline form.
  • the present invention can provide a new diaphragm for a liquid fuel cell suitable for a liquid fuel cell, particularly an alkaline liquid fuel cell.
  • the diaphragm may include a polymer base material and a hydrophilic functional group present on the polymer base material.
  • the material for the polymer substrate those described later as the material for the polymer porous membrane can be used.
  • the polymer substrate may be a porous membrane (polymer porous membrane).
  • the hydrophilic functional group present on the polymer substrate is preferably obtained by carrying out a hydrophilic treatment.
  • the diaphragm for a liquid fuel cell can be formed through a step of preparing a polymer porous membrane and a step of hydrophilizing the polymer porous membrane.
  • hydrophilic treatment is not particularly limited, and graft polymerization treatment, corona treatment, plasma treatment, sputtering treatment, sulfonation treatment, treatment using a surfactant or a hydrophilic polymer, and the like may be used.
  • a solution containing the hydrophilic polymer is applied to the polymer porous membrane, and the hydrophilic polymer membrane is formed on the surface and pore walls of the polymer porous membrane, thereby A hydrophilic functional group may be added to the surface.
  • the amount of the hydrophilic functional group can be adjusted by the thickness of the film formed by applying the hydrophilic polymer, and the average pore diameter of the diaphragm in the film can be adjusted by the thickness of the film. .
  • the hydrophilization treatment is preferably performed using a graft polymerization method from the viewpoint that it can be treated in a uniform system.
  • the diaphragm for a liquid fuel cell includes a polymer substrate and a graft chain introduced into the polymer substrate, and the graft chain preferably has a hydrophilic functional group.
  • Air permeability of the membrane of the present embodiment is preferably in the range of 100 ⁇ 2000sec / 100ml ⁇ inch 2 , more preferably in the range of 200 ⁇ 1000sec / 100ml ⁇ inch 2 . If the air permeability becomes too large, the amount of water permeation and the water permeation rate may decrease. As a result, water required for the reaction at the cathode catalyst may be insufficient, and the reaction efficiency at the cathode catalyst may be reduced.
  • the diaphragm of the present embodiment preferably has a methanol retention rate of 20% or more.
  • the methanol liquid retention rate of the diaphragm is a 23-degree relative humidity measured by using a diaphragm that was previously cut into a rectangle having a long side of 50 mm and a short side of 10 mm and left standing in an atmosphere of 23 ° C. and 50% relative humidity for 12 hours or more.
  • the long side of the rectangle is perpendicular to the liquid level of methanol, and the test piece is held against methanol in a state where the portion 5 mm from the bottom of the test piece is immersed in methanol. Is the ratio of the liquid absorption height from the liquid surface to the long side after maintaining for 1 minute.
  • the methanol retention rate (methanol retention rate) of the diaphragm is measured.
  • the fuel liquid is an aqueous fuel solution in which fuel is dissolved in water, and dissolves an electrolyte.
  • Methanol can be dissolved in water and supplied to the liquid fuel cell as a fuel solution.
  • methanol is relatively similar in structure and molecular weight to water used in fuel solutions. Therefore, it is considered that an appropriate result for evaluating the fuel liquid retention rate of the diaphragm can be obtained by measuring the methanol liquid retention rate.
  • the diaphragm capable of retaining the fuel liquid can hold the electrolyte dissolved in the fuel liquid together with the fuel liquid. Since this electrolyte is responsible for ionic conductivity in the fuel cell, the use of a diaphragm having a good methanol retention rate improves the ionic conductivity and suppresses the electrical resistance in the fuel cell during power generation. If the amount of electrolyte contained in the diaphragm is too small, power generation may not be possible, and even when power generation is possible, the electrical resistance of the fuel cell during power generation may increase. A diaphragm having a methanol liquid retention rate in the above range can satisfactorily retain water contained in the fuel liquid.
  • the diaphragm of this embodiment can contribute to the improvement of the efficiency of the oxygen reduction reaction at the cathode, and can contribute to the improvement of the power generation efficiency of the battery.
  • a liquid fuel cell an alkaline liquid fuel cell
  • fuel is supplied to the anode side and an oxidant such as air is supplied to the cathode side.
  • a liquid fuel cell includes a membrane-electrode assembly (MEA) in which a diaphragm and a catalyst layer are integrated.
  • MEA membrane-electrode assembly
  • auxiliary equipment such as a humidifier.
  • water that has passed through the diaphragm from the anode side to the cathode side In this case, it is conceivable to use a diaphragm that can penetrate water well.
  • the present invention from still another aspect, It is a porous membrane having a methanol retention rate of 20% or more.
  • a diaphragm for a liquid fuel cell is provided.
  • the liquid fuel cell is preferably in alkaline form.
  • the present invention can provide a diaphragm for a liquid fuel cell that can contribute to improving the characteristics of the liquid fuel cell.
  • the liquid fuel cell membrane preferably has a hydrophilic functional group.
  • a hydrophilic functional group By providing a hydrophilic functional group, the liquid retention of methanol can be improved.
  • the hydrophilic functional group may be a functional group having ion conductivity.
  • a known porous film can be used. Examples thereof include a porous film made of an inorganic base material and a porous film made of a polymer base material.
  • a porous film made of a polymer substrate can be formed, for example, by polymerizing a polymerizable monomer having a hydrophilic functional group.
  • a hydrophilic functional group may be introduced on the surface of the porous membrane by performing a hydrophilic treatment.
  • This fuel cell membrane is measured by increasing the air pressure by supplying air to the second main surface opposite to the first main surface while supplying water to the first main surface.
  • the pressure resistance between the main surfaces of the diaphragm is preferably 60 kPa or more, more preferably 80 kPa or more, and further preferably 100 kPa or more.
  • the weight of the membrane of the present embodiment is preferably in the range of 1.05 to 3.0 times (graft rate 5 to 200%) of the weight of the polymer porous membrane, and 1.15 to 2.0 times (graft).
  • the ratio is more preferably in the range of 15% to 100%.
  • the graft ratio indicates the ratio of the weight difference between the weight of the film after graft polymerization and the weight of the film before graft polymerization with respect to the weight of the film before graft polymerization.
  • the material of the polymer porous membrane contained in the diaphragm of the present embodiment is not particularly limited, and a known resin can be used as long as the effect of the invention is not impaired.
  • a known resin can be used as long as the effect of the invention is not impaired.
  • polyolefin resins such as polyethylene and polypropylene, polystyrene resins, epoxy resins such as bisphenol A type epoxy polymers, polysulfide resins such as polyphenylene sulfide, polyether resins such as polyether ketone, polyvinylidene fluoride, ethylene tetrafluoro Fluorine resins such as ethylene and polytetrafluoroethylene
  • polyolefin resins such as polyethylene and polypropylene
  • polystyrene resins epoxy resins such as bisphenol A type epoxy polymers
  • polysulfide resins such as polyphenylene sulfide
  • polyether resins such as polyether ketone
  • At least one selected from the group consisting of polyethylene, polypropylene, polystyrene, bisphenol A type epoxy polymer, polyphenylene sulfide, polyether ketone, polyvinylidene fluoride, ethylene tetrafluoroethylene, and polytetrafluoroethylene is included. It is preferable that at least one selected from the group consisting of polyethylene, polypropylene, polystyrene, polyphenylene sulfide and polyether ketone is included, and at least one selected from the group consisting of polyethylene, polypropylene and polystyrene is included. More preferably.
  • polyethylene is preferable, and low density polyethylene, high density polyethylene, and ultrahigh molecular weight polyethylene are more preferable.
  • High-density polyethylene and ultrahigh molecular weight polyethylene are particularly preferable from the viewpoint of improving the strength and heat resistance of the polymer porous membrane.
  • ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more, particularly 1,000,000 or more is preferable. These resins may be used alone or in admixture of two or more.
  • These resins may be cross-linked.
  • the crosslinking method is not particularly limited, and a known method such as a method of irradiating the resin with an electron beam or the like, a method of adding a crosslinking agent such as a silane compound or an organic peroxide, and the like can be used.
  • a cross-linked resin is used, the strength of the polymer base material may be improved and the effect of preventing the short circuit of the electrode may be improved.
  • the average pore diameter of the polymer porous membrane is preferably in the range of 1 nm to 1000 nm, more preferably in the range of 2 nm to 500 nm, and still more preferably in the range of 5 nm to 300 nm. If the average pore diameter becomes too large, a short circuit between the electrodes may occur. In addition, the pressure resistance of the diaphragm may be reduced, making it difficult to withstand the pressure of the oxidant. Also, the amount of fuel permeation may increase. If the average pore diameter becomes too small, the water permeability may be lowered. If the water permeation amount is too small, water required for the reaction in the cathode catalyst may be insufficient, and power generation efficiency may be reduced. Since the average pore diameter of the entire diaphragm varies due to graft polymerization performed later, it is preferable to adjust the average pore diameter of the porous membrane in consideration of the variation.
  • the porosity of the polymer porous membrane is preferably in the range of 5 to 95%, more preferably in the range of 10 to 70%, and still more preferably in the range of 10% to 50%. If the porosity is too high, fuel permeation may increase. In addition, the pressure resistance of the diaphragm is reduced, and the pressure of the oxidant may not be maintained. If the porosity is too small, the water permeability may be too small, and the moisture content may be lowered. Since the porosity of the whole diaphragm varies due to graft polymerization performed later, it is preferable to adjust the porosity of the porous membrane in consideration of the variation.
  • the film thickness of the polymer porous film is preferably in the range of 5 ⁇ m to 100 ⁇ m, and more preferably in the range of 10 ⁇ m to 50 ⁇ m. If the film thickness becomes too thin, the film strength may decrease, and defects such as film breakage and pinholes may occur.
  • the fuel permeation amount and water permeation amount may increase. When the permeation amount of the fuel increases, a side reaction in which the fuel and the oxidant directly react with each other occurs, so that the power generation efficiency may deteriorate, and the side reaction may cause deterioration of the cathode catalyst and the like.
  • the resistance (film resistance) as a film in the diaphragm may increase.
  • the water permeability may be too small. If the water permeation amount is too small, water required for the reaction in the cathode catalyst may be insufficient, and power generation efficiency may be reduced.
  • the amount of permeated fuel increases and the fuel is present on the cathode catalyst, a side reaction in which the fuel and the oxidant directly react may occur, resulting in a decrease in power generation efficiency of the battery, and deterioration of the cathode catalyst and the like due to the side reaction.
  • the method for producing the polymer porous membrane is not particularly limited, and a known method such as a dry film formation method or a wet film formation method using thermally induced phase separation or non-solvent induced phase separation can be used.
  • a foaming method using an inorganic foaming agent, an organic foaming agent or a supercritical fluid, a polymer substrate having low compatibility and a phase separation agent are mixed and then phase separated, Extraction or heating using a solvent for extraction (for example, supercritical carbon dioxide), forming a molded body containing components that can be extracted after film formation, phase separation, cutting to form a film
  • a processing method for removing extractable components from the membrane is possible to use.
  • a powdery polymer base material filled in a mold (for example, a cylindrical shape) is heated using water vapor and sintered to form a molded body, and the formed body (for example, a cylindrical block body).
  • the porous film may be obtained by cutting the film into a predetermined thickness.
  • a solvent-containing treatment may be performed after melt-kneading a composition containing a resin and a solvent, cooling after extrusion to form a sheet-like molded product.
  • a laminated polymer porous membrane can be obtained by rolling or uniaxially stretching the sheet-like molded product and then laminating and extracting and removing the solvent. Moreover, after laminating, it may be stretched. It is also possible to bond and laminate immediately after extraction. In that case, the extraction process can be completed in a short time, so that productivity can be improved.
  • the solvent used for preparing the polymer porous membrane is not particularly limited as long as it can dissolve the resin contained in the polymer porous membrane, but a solvent having a freezing point of ⁇ 10 ° C. or lower is preferably used.
  • a solvent having a freezing point of ⁇ 10 ° C. or lower is preferably used.
  • aliphatic or alicyclic hydrocarbons such as decane, decalin and liquid paraffin, and mineral oil fractions having boiling points corresponding to these.
  • the mixing ratio of the resin and the solvent in the composition containing the resin and the solvent cannot be generally determined, but the concentration of the resin in the composition is preferably in the range of 5 to 30% by weight. If the concentration of the resin is too high, kneading is insufficient and it becomes difficult to obtain sufficient entanglement of the polymer chains. If the resin concentration is too low, sufficient strength of the polymer porous membrane may not be obtained.
  • additives such as an antioxidant, an ultraviolet absorber, a dye, a pigment, an antistatic agent, and nucleation are further added as long as the object of the present invention is not impaired. Can be added.
  • the hydrophilic functional group is not particularly limited as long as it is a functional group having hydrophilicity.
  • the hydrophilic functional group is at least one selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, a sulfonic acid group, and a phosphoric acid group. Yes, especially a carboxyl group.
  • the graft chain may not substantially have a functional group having anion exchange ability. “Substantially free” means that the amount of the functional group having anion exchange capacity relative to the weight of the diaphragm is 0.1 mmol / g or less, preferably 0.05 mmol / g or less.
  • functional groups having anion exchange ability include quaternary ammonium bases and quaternary phosphonium bases.
  • the hydrophilic functional group may have a monomer that forms a graft chain (hereinafter sometimes referred to as “graft monomer (M)”), and may be introduced into the graft chain after graft polymerization. That is, the graft monomer (M) may have a hydrophilic functional group or may have a site where a hydrophilic functional group can be introduced.
  • graft monomer (M) may have a hydrophilic functional group or may have a site where a hydrophilic functional group can be introduced.
  • the graft monomer (M) has a carbon-carbon unsaturated bond and a hydrophilic functional group.
  • the graft monomer (M) is not particularly limited, but examples thereof include carboxylic acid monomers such as acrylic acid and methacrylic acid, acrylamide, methacrylamide, 2-hydroxymethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxy (Meth) acrylic acid derivative monomers such as propyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxymethyl methacrylate, 2-hydroxyethyl methacrylate, vinyl acetate monomers such as vinyl acetate, allylamine, acrylamide, methacrylamide, N-vinyl Examples thereof include nitrogen-containing monomers such as pyrrolidone and N-vinylpyridine, and styrene derivative monomers such as sodium styrenesulfonate.
  • At least one selected from the group consisting of acrylic acid, methacrylic acid, acrylamide, methacrylamide, N-vinylpyrrolidone, N-vinylpyridine, 2-hydroxyethyl methacrylate, and styrene derivative monomers Preferably, at least one selected from the group consisting of acid, methacrylic acid, acrylamide, methacrylamide, N-vinyl pyrrolidone, N-vinyl pyridine, and 2-hydroxyethyl methacrylate is included.
  • the graft monomer (M) of the present embodiment has substantially no functional group having anion exchange ability. “Substantially free” means that the amount of the functional group having anion exchange capacity relative to the weight of the diaphragm is 0.1 mmol / g or less, preferably 0.05 mmol / g or less.
  • functional groups having anion exchange ability include quaternary ammonium bases and quaternary phosphonium bases.
  • the graft monomer (M) may be used for polymerization alone or may be prepared as a solution (graft monomer (M) solution) in which the graft monomer (M) is dissolved in a solvent.
  • the solvent contained in the graft monomer (M) solution is not particularly limited. If a solvent that dissolves the graft monomer (M) but does not dissolve the polymer porous membrane is used, the graft monomer (M), the polymer porous membrane, Is easily separated. In addition, when a solvent capable of dissolving a polymer formed only from the graft monomer (M) as a by-product is used, the polymerization solution can be kept uniform.
  • the solubility of the graft monomer (M), the polymer formed only from the graft monomer (M) and the polymer porous membrane in the solvent is the polymer formed only from the graft monomer (M), the graft monomer (M), and Since it may vary depending on the structure or polarity of the polymer porous membrane, a solvent may be appropriately selected according to the solubility of these compounds. Two or more compounds may be mixed and used as a solvent.
  • Such a solvent include aromatic compounds such as aromatic hydrocarbons such as benzene, toluene and xylene, and phenols such as phenol and cresol.
  • aromatic compounds such as aromatic hydrocarbons such as benzene, toluene and xylene, and phenols such as phenol and cresol.
  • aromatic compound dissolves the polymer composed only of the graft monomer (M) as a by-product, the polymerization solution can be kept uniform.
  • the concentration of the graft monomer (M) in the graft monomer (M) solution may be determined according to the polymerizability of the graft monomer (M) and the target graft ratio. It is preferable to include 20% by weight or more of the graft monomer (M) based on the weight. By using a solution having a concentration of the graft monomer (M) of 20% by weight or more, it is easy to avoid a situation in which the graft reaction does not proceed sufficiently.
  • oxygen in the graft monomer (M) or the graft monomer (M) solution is subjected to a known method such as freeze degassing or bubbling using nitrogen gas. It is preferable to use and remove.
  • the graft chain is introduced into the polymer porous membrane by graft polymerization.
  • This graft chain is bonded to the polymer porous membrane.
  • the graft chain is preferably formed by a radiation graft polymerization treatment from the viewpoint that it can be treated in a homogeneous system. Specifically, it is formed by irradiating a polymer porous membrane with radiation, bringing the polymer porous membrane after radiation irradiation into contact with a graft monomer (M) or a graft monomer (M) solution to cause a graft polymerization reaction. It is preferable.
  • Examples of radiation irradiated to the polymer porous membrane include ionizing radiation such as ⁇ rays, ⁇ rays, ⁇ rays, electron rays, and ultraviolet rays, and ⁇ rays or electron rays are particularly preferable.
  • the irradiation dose is preferably in the range of 1 kGy to 400 kGy, more preferably in the range of 10 kGy to 300 kGy.
  • the graft rate can be controlled by the radiation dose. If the irradiation dose is too low, the graft rate may be lowered. When the irradiation dose increases too much, the mechanical strength of the diaphragm may be reduced due to deterioration of the polymer porous membrane or excessive polymerization reaction.
  • the polymer porous membrane after irradiation may be held at a low temperature (for example, ⁇ 30 ° C. or lower).
  • the graft polymerization is preferably performed in an atmosphere where the oxygen concentration is as low as possible, and is performed in an inert gas atmosphere such as argon gas or nitrogen gas. Is more preferable.
  • the temperature at which the graft polymerization is performed is, for example, 0 ° C. to 100 ° C., particularly 40 to 80 ° C.
  • the reaction time for carrying out the graft polymerization is, for example, about 2 minutes to 12 hours.
  • the graft ratio can be controlled by these reaction temperature and reaction time.
  • graft polymerization reaction a reaction example in a solid-liquid two-phase system will be described.
  • a graft monomer (M) solution containing a graft monomer (M) and a solvent is placed in a container such as glass or stainless steel.
  • vacuum degassing in the graft monomer (M) solution and bubbling with an inert gas (nitrogen gas or the like) are performed.
  • an inert gas nitrogen gas or the like
  • Graft chains are introduced into the polymer constituting the polymer porous membrane by graft polymerization.
  • the obtained membrane is removed from the reaction solution and filtered. Further, in order to remove the polymer composed of only the solvent, the unreacted graft monomer (M), and the graft monomer (M), the obtained film is washed 3 to 6 times with an appropriate amount of solvent and then dried.
  • the solvent a solvent that can easily dissolve the graft monomer (M) and the polymer composed only of the graft monomer (M) and does not dissolve the graft film may be used.
  • water, toluene, acetone or the like can be used as the solvent.
  • the graft monomer (M) has a carbon-carbon unsaturated bond and a site capable of introducing a hydrophilic functional group.
  • the site capable of introducing a hydrophilic functional group is, for example, a halogenated alkyl group such as a halogenated methyl group, a halogenated ethyl group, a halogenated propyl group, and a halogenated butyl group, styrene sulfonic acid, vinyl sulfonic acid or acrylic phosphone.
  • alkyl esters such as acids.
  • graft monomer (M) examples include styrene derivatives such as styrene, chloromethylstyrene, and bromobutylstyrene. These monomers (M) may be used alone or in admixture of two or more. In this embodiment, it is preferable that the graft monomer (M) does not have a functional group having anion exchange ability.
  • the graft chain of the diaphragm does not substantially have a functional group having cation conductivity.
  • the hydrophilic functional group which the diaphragm of this embodiment has is a sulfonic acid group, for example.
  • the diaphragm having the characteristics of the present invention has a pore filled with a hydrophilic gel, a nonporous membrane made of a polymer base material having a hydrophilic functional group, or a polymer material having a hydrophilic functional group. It is the made porous membrane. If necessary, the polymer material having a hydrophilic functional group may have a crosslinked structure.
  • Weight maintenance rate (%) (weight after KOH treatment) ⁇ 100 / (weight before KOH treatment)
  • (F) Pressure resistance test evaluation of pressure resistance between main surfaces
  • a pressure resistance test was performed using the evaluation cell for fuel cell shown in FIGS. 2 to 4 as an evaluation cell, and the pressure resistance between the main surfaces of the diaphragm was evaluated.
  • a diaphragm 2 having a main surface of a square having a side of 4 cm was prepared.
  • the diaphragm 2 was sandwiched between a pair of gaskets 11 and 21 having square openings 11a and 21a each having a length of 2 cm.
  • a pair of separators 12 and 22 with serpentine-structured flow channels 12a and 22a, a pair of current collector plates 13 and 23, and a pair of end plates 14 and 24 are arranged and sandwiched in this order on the outside of the gaskets 11 and 21.
  • the evaluation cell 100 has flow paths 18, 19, 28, and 29.
  • the channels 18 and 19 are channels for supplying and discharging water, respectively, and the channels 28 and 29 are channels for supplying and discharging dry air, respectively.
  • Each flow path 18, 19, 28, 29 has an opening in the end plate.
  • the flow paths 18 and 19 penetrate the end plate 14, the current collector plate 13, and the separator 12, and are connected to the flow path 12a. The same applies to the flow paths 28 and 29.
  • the evaluation cell 100 was installed so that the main surface of the diaphragm 2 was along the vertical direction. Supply of water and dry air to the evaluation cell 100 in this state was started. 2 ml of water per minute is supplied to the main surface on the anode side (first main surface) via a pipe 38 connected to the flow path 18, and 500 ml per minute is supplied to the main surface on the cathode side (second main surface). Dry air was supplied through a pipe 48 connected to the flow path 28. By continuing to supply water as described above, the inside of the first main surface side of the cell 100 was filled with the supplied water, and the first main surface of the diaphragm 2 was always in contact with water.
  • the evaluation cell 100 was heated using the rubber heaters 15 and 25 provided on the end plates 14 and 24 so that the temperature of the evaluation cell 100 became 80 ° C.
  • the temperature of the evaluation cell 100 was measured using a thermocouple 41 installed in the separator 22. Water and dry air were continuously supplied as described above, and the temperature of the evaluation cell 100 was maintained at 80 ° C. for 1 hour.
  • the pressure of the dry air to the second main surface was measured for 10 minutes.
  • the pressure resistance between the main surfaces of the diaphragm was evaluated as 0 kPa.
  • the opening of the pressure regulator 43 is adjusted while maintaining the temperature of the evaluation cell 100 at 80 ° C., and the second main The pressure of the dry air to the second main surface was increased so that the pressure of the dry air to the surface was 40 kPa.
  • the pressure regulator 43 continues to supply water and dry air as described above so that the pressure of the dry air to the second main surface can be maintained at 40 kPa while maintaining the temperature of the evaluation cell 100 at 80 ° C.
  • the opening degree of was adjusted. With the water and dry air supply rates, the temperature of the evaluation cell 100, and the opening degree of the pressure adjusting device 43 maintained, the pressure of the dry air to the second main surface was measured for 10 minutes. When 40 kPa could not be maintained for 10 minutes, the pressure resistance between the main surfaces of the diaphragm was evaluated as 20 kPa.
  • the pressure of dry air to the second main surface was increased, and the same measurement was performed in the order of 60 kPa, 80 kPa, and 100 kPa.
  • the pressure resistance between the main surfaces of the diaphragm was evaluated as 100 kPa.
  • the case where the pressure can be maintained means that the change in the pressure of the dry air to the second main surface is 1 kPa or less in 10 minutes.
  • the water permeation rate was measured according to the following procedure using the evaluation cell for fuel cell shown in FIGS. 2 to 4 as the evaluation cell.
  • a measurement diaphragm a water permeability measurement diaphragm 2 having a square main surface with a side of 4 cm and a W3 measurement diaphragm having a rectangular main surface with a short side of 2 cm and a long side of 3 cm were prepared.
  • the diaphragm 2 for measuring the water transmission rate was sandwiched between a pair of gaskets 11 and 21 having square openings 11a and 21a each having a length of 2 cm.
  • a pair of separators 12 and 22 with flow paths 12a and 22a having a serpentine structure, a pair of current collector plates 13 and 23, and a pair of end plates 14 and 24 are arranged in this order on the outside of the gaskets 11 and 21 so as to sandwich the diaphragm 2 did.
  • Each member was fastened using a fixing component (not shown) such as a bolt so that air and water did not leak from each contact surface of the member, and the evaluation cell 100 was formed.
  • the evaluation cell 100 has flow paths 18, 19, 28, and 29.
  • the channels 18 and 19 are channels for supplying and discharging water, respectively, and the channels 28 and 29 are channels for supplying and discharging dry air, respectively.
  • Each flow path 18, 19, 28, 29 has an opening in the end plate.
  • the flow paths 18 and 19 penetrate the end plate 14, the current collector plate 13, and the separator 12, and are connected to the flow path 12a. The same applies to the flow paths 28 and 29.
  • the evaluation cell 100 was installed so that the main surface of the diaphragm 2 was along the vertical direction. Supply of water and dry air to the evaluation cell 100 in this state was started. 2 ml of water per minute is supplied to the first main surface via a pipe 38 connected to the flow path 18, and 500 ml of dry air per minute is supplied to the second main face via a pipe 48 connected to the flow path 28. Supplied. At this time, the evaluation cell 100 was heated using the rubber heaters 15 and 25 provided on the end plates 14 and 24 so that the temperature of the evaluation cell 100 became 80 ° C. The temperature of the evaluation cell 100 was measured using a thermocouple 41 installed in the separator 22. Water and dry air were continuously supplied to the evaluation cell 100 as described above, and the temperature of the evaluation cell 100 was maintained at 80 ° C. for 1 hour.
  • the water and dry air are continuously supplied as described above, and the water discharged from the pipe 39 connected to the anode-side flow path 19 is collected for 30 minutes while maintaining the temperature of the evaluation cell 100 at 80 ° C. did.
  • the weight of the collected water was W2.
  • the weight of water supplied to the evaluation cell 100 for 30 minutes was defined as W1.
  • the weight per cm 2 of the diaphragm calculated from the measured weight was defined as W3.
  • the water transmission rate in the cross-sectional direction of the diaphragm was calculated according to the following formula.
  • (J) Methanol retention ratio A diaphragm, which was previously cut into a rectangle having a long side of 50 mm and a short side of 10 mm, and left in an atmosphere of 23 ° C. and 50% relative humidity for 12 hours or more, was used as a test piece. Hold the test piece against methanol in a state where the long side of the rectangle is perpendicular to the methanol surface and the 5 mm portion from the bottom of the test piece is immersed in methanol in an atmosphere of 23 ° C and 50% relative humidity. did.
  • the methanol retention rate is the ratio of the liquid absorption height from the liquid surface of methanol after maintaining this state for 1 minute to the long side.
  • the test piece before liquid absorption is opaque, and the test piece which absorbed methanol is translucent. The length of the translucent test piece was measured to obtain the liquid absorption height.
  • a power generation test was conducted at 2 ml of liquid fuel per minute was supplied to the anode side, and 200 ml of dry air was supplied to the cathode side. In this test, whether or not current sweep is possible, the limit current density, and the cell resistance when the maximum output density was developed (measured using the current interruption method. The internal resistance of the cell was measured from the voltage change when the current was instantaneously interrupted. ) And the maximum power density were compared.
  • Example 1 In Example 1, an ultrahigh molecular weight polyethylene porous film having a film thickness of 20 ⁇ m, a porosity of 40%, and an air permeability (Gurley value) of 173 sec / 100 ml ⁇ inch 2 was used as the polymer substrate. By irradiating this ultrahigh molecular weight polyethylene porous film with an electron beam of 45 kGy, free radicals were generated. The ultrahigh molecular weight polyethylene porous film after electron beam irradiation was cooled to ⁇ 70 ° C. and stored until the next step was performed.
  • the obtained graft porous membrane was pulled up and washed with water to wash away excess monomers, and then water on the surface portion was removed to obtain a hydrophilic diaphragm having hydrophilicity.
  • the resulting graft porous membrane had a graft rate of 40%.
  • Each physical property of this diaphragm was measured.
  • This membrane had an air permeability (Gurley value) of 491 sec / 100 ml ⁇ inch 2 . A power generation test was performed using this diaphragm.
  • Example 2 Except for making graft polymerization time into 4 minutes, it implemented similarly to Example 1 and obtained the hydrophilic membrane with a graft ratio of 30%. Each physical property of this diaphragm was measured. This membrane had an air permeability (Gurley value) of 366 sec / 100 ml ⁇ inch 2 . In addition, a power generation test was performed using this diaphragm.
  • Example 1 The ultra high molecular weight polyethylene porous membrane used in Example 1 was used as a membrane without treatment. Each physical property of this diaphragm was measured. This membrane had an air permeability (Gurley value) of 173 sec / 100 ml ⁇ inch 2 . In addition, a power generation test was performed using this diaphragm.
  • a nonporous film of a copolymer of tetrafluoroethylene and ethylene (ETFE, film thickness 50 ⁇ m) was used.
  • This ETFE film was irradiated with an electron beam of 30 kGy on each side (total 60 kGy) under vacuum at room temperature to generate free radicals.
  • the ETFE film after electron beam irradiation was cooled to ⁇ 70 ° C. and stored until the next step was performed.
  • 28 g of 4- (chloromethyl) styrene and 12 g of xylene were mixed to prepare a monomer solution.
  • this monomer solution was bubbled with nitrogen gas to remove oxygen in the monomer solution.
  • the graft membrane after the quaternization treatment was washed with ethanol for 30 minutes, then washed with an ethanol solution containing 1N hydrochloric acid for 30 minutes, and further washed with pure water.
  • a polymer base material was an ETFE film, and a film having a chloride ion type quaternary ammonium base was obtained. Each physical property of this diaphragm was measured. In addition, a power generation test was performed using this diaphragm.
  • Table 1 summarizes the results of battery tests using the diaphragms of Examples 1-2 and Comparative Examples 1-2.
  • PE represents ultrahigh molecular weight polyethylene
  • CMS represents chloromethylstyrene
  • TMA represents trimethylamine.
  • Comparative Example 1 polyethylene porous membrane having no hydrophilic functional group
  • Comparative Example 2 EFE nonporous film
  • current flowed but the internal resistance of the cell was high and the limiting current density was low.
  • Examples 1 and 2 polyethylene porous membrane
  • the limiting current density was higher than that of Comparative Example 2, and the cell resistance when the maximum output density was developed was lower than that of Comparative Example 2.

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Abstract

　The disclosed liquid fuel cell partitioning membrane is provided with, e.g., a polymeric porous membrane and a graft chain introduced into the polymeric porous film. The graft chain contains a hydrophilic functional group. The hydrophilic functional group is preferably a hydroxyl group, a carboxyl group, an amino group, etc.

Description

液体燃料電池用隔膜及びそれを備えた膜－電極接合体Membrane for liquid fuel cell and membrane-electrode assembly including the same
　本発明は、液体燃料電池用隔膜及びそれを備えた膜－電極接合体に関する。 The present invention relates to a diaphragm for a liquid fuel cell and a membrane-electrode assembly including the same.
　高分子電解質型燃料電池（ＰＥＦＣ）は、燃料電池としては低い温度での動作が可能であるとともに、出力密度が高い等の利点を有し、将来の普及に期待が寄せられている。ＰＥＦＣは、アノードとカソードとの間に隔膜を備えており、隔膜としてはイオン伝導性を有する高分子電解質膜が用いられる。この隔膜としては、カチオン交換膜が用いられてきた。近年では、白金を触媒に用いることなく発電が可能なアニオン交換膜を用いたＰＥＦＣが報告されている（例えば、特許文献１、特許文献２）。 The polymer electrolyte fuel cell (PEFC) has advantages such as being able to operate at a low temperature as a fuel cell and having a high output density, and is expected to spread in the future. The PEFC includes a diaphragm between the anode and the cathode, and a polymer electrolyte membrane having ion conductivity is used as the diaphragm. As this diaphragm, a cation exchange membrane has been used. In recent years, PEFCs using an anion exchange membrane that can generate electricity without using platinum as a catalyst have been reported (for example, Patent Document 1 and Patent Document 2).
　一方、水素よりも取り扱いが容易なメタノール等の液体を燃料として用いた燃料電池（液体燃料電池）が検討されている。 On the other hand, a fuel cell (liquid fuel cell) using a liquid such as methanol that is easier to handle than hydrogen as a fuel is being studied.
特開２０００－３３１６９３号公報JP 2000-331693 A 特表２０１０－５１６８５３号公報Special table 2010-516853 gazette
　液体燃料電池用隔膜は、隔膜中に水溶液を含浸させて使用する。従って、液体燃料電池用隔膜には、水溶液を含浸させた場合の変形を防ぐために、水溶液の含侵前後において面積の膨張が小さいことが求められる。 The liquid fuel cell diaphragm is used by impregnating the diaphragm with an aqueous solution. Therefore, the diaphragm for liquid fuel cells is required to have a small area expansion before and after impregnation with the aqueous solution in order to prevent deformation when the aqueous solution is impregnated.
　一方、液体燃料電池の運転時に、隔膜に含まれる水溶液のｐＨは酸性又はアルカリ性となる。例えば、カソードにおける酸化還元反応により生じたアニオン（ＯＨ-）の移動を利用した液体燃料電池（以下、アルカリ形液体燃料電池）においては、水溶液のｐＨはアルカリ性になる。従って、隔膜には水溶液のｐＨに対する良好な化学的耐久性が求められる。 On the other hand, during operation of the liquid fuel cell, the pH of the aqueous solution contained in the diaphragm becomes acidic or alkaline. For example, in a liquid fuel cell (hereinafter referred to as an alkaline liquid fuel cell) utilizing the movement of anions (OH − ) generated by the oxidation-reduction reaction at the cathode, the pH of the aqueous solution becomes alkaline. Accordingly, the diaphragm is required to have good chemical durability against the pH of the aqueous solution.
　本発明は、液体燃料電池用隔膜に関し、面積膨潤率が小さく、化学的耐久性が良好である液体燃料電池用隔膜を提供することを目的とする。 The present invention relates to a diaphragm for a liquid fuel cell, and an object thereof is to provide a diaphragm for a liquid fuel cell having a small area swelling rate and good chemical durability.
　一般に、燃料電池用の隔膜としてはイオン交換膜が用いられ、これらの膜は無孔膜である。本発明者等の鋭意研究の結果、驚くべきことに、親水性官能基を有する高分子多孔膜を用いることによって、面積膨潤率が小さく、化学的な耐久性が良好である液体燃料電池用隔膜を得られることが分かった。 Generally, ion-exchange membranes are used as diaphragms for fuel cells, and these membranes are non-porous membranes. As a result of diligent research by the present inventors, surprisingly, by using a polymer porous membrane having a hydrophilic functional group, a membrane for a liquid fuel cell having a small area swelling rate and good chemical durability. I found out that
　本発明は、
　液体燃料電池用隔膜であって、
　高分子多孔膜と、
　前記高分子多孔膜に導入されたグラフト鎖と、
を備え、
　前記グラフト鎖は親水性官能基を含む、
　液体燃料電池用隔膜、を提供する。 The present invention
A diaphragm for a liquid fuel cell,
A polymer porous membrane,
Graft chains introduced into the polymer porous membrane;
With
The graft chain includes a hydrophilic functional group;
A diaphragm for a liquid fuel cell is provided.
　さらに別の側面において、本発明は、
　本発明の液体燃料電池用隔膜を備えた膜－電極接合体（ＭＥＡ）、を提供する。 In yet another aspect, the present invention provides:
There is provided a membrane-electrode assembly (MEA) comprising a diaphragm for a liquid fuel cell of the present invention.
　本発明によれば、面積膨潤率が小さく、化学的な耐久性が高い液体燃料電池用隔膜を提供することができる。本発明によれば、この隔膜の特性を活かしたＭＥＡを得ることができる。 According to the present invention, it is possible to provide a diaphragm for a liquid fuel cell having a small area swelling rate and high chemical durability. According to the present invention, an MEA that takes advantage of the characteristics of the diaphragm can be obtained.
本発明のＭＥＡの一例を模式的に示す断面図である。It is sectional drawing which shows typically an example of MEA of this invention. 透水速度試験又は耐圧性試験に用いる評価用セルを模式的に示す分解斜視図である。It is a disassembled perspective view which shows typically the cell for evaluation used for a water-permeation rate test or a pressure resistance test. 図２のIII－III面における模式的な評価用セルの縦断面図である。FIG. 3 is a longitudinal sectional view of a schematic evaluation cell on the III-III plane of FIG. 2. 透水速度試験又は耐圧性試験に用いる評価用セルを模式的に示す正面図である。It is a front view which shows typically the cell for evaluation used for a water transmission rate test or a pressure resistance test.
　以下に本発明の好ましい実施形態を説明するが、本発明はこれに限定されるものではない。なお、以下において、重複する説明は省略する。 Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited thereto. In the following, redundant description is omitted.
　以下において、アルカリ形液体燃料電池又はこの液体燃料電池に用いられるＭＥＡもしくは隔膜を例として述べるが、本発明の液体燃料電池用隔膜はこれに限らず、酸形液体燃料電池にも用いることができる。 In the following, an alkaline liquid fuel cell or an MEA or a diaphragm used for the liquid fuel cell will be described as an example. However, the liquid fuel cell diaphragm of the present invention is not limited to this and can be used for an acid liquid fuel cell. .
　本実施形態のＭＥＡは、液体燃料電池内における使用に適している。この液体燃料電池は、ＭＥＡ以外の部分に特に限定はなく、公知の部材を適用できる。 The MEA of this embodiment is suitable for use in a liquid fuel cell. This liquid fuel cell is not particularly limited to a portion other than the MEA, and a known member can be applied.
　以下で述べる液体燃料電池は、本実施形態のＭＥＡを備えたアルカリ形液体燃料電池であり、アノード側には液体燃料が、カソード側には酸化剤が供給される。酸化剤は、例えば空気である。 The liquid fuel cell described below is an alkaline liquid fuel cell equipped with the MEA of the present embodiment, and liquid fuel is supplied to the anode side and oxidant is supplied to the cathode side. The oxidizing agent is air, for example.
　液体燃料は水に溶解された燃料であり、電解質を溶解している。燃料は、水に溶解可能であれば特に限定はなく、例えば、メタノール、エタノール等の低級アルコール類、ヒドラジン（水和物）、アンモニア等のアミン類、水素化ホウ素ナトリウム等が挙げられ、反応性が高く、発電原理上ＣＯ2を発生しないことから、ヒドラジン（水和物）が好ましい。 The liquid fuel is a fuel dissolved in water and dissolves an electrolyte. The fuel is not particularly limited as long as it can be dissolved in water. Examples thereof include lower alcohols such as methanol and ethanol, amines such as hydrazine (hydrate) and ammonia, sodium borohydride, and the like. Hydrazine (hydrate) is preferable because it is high and does not generate CO 2 on the principle of power generation.
　燃料の供給量は、液体燃料中の燃料の濃度や供給速度（流量）によって制御することが可能である。必要な燃料の量は、取り出す電流量に応じて変化する。従って、取り出す電流量に応じてアノード側に供給する燃料の供給量を制御することが好ましい。取り出す電流量に対して過剰の燃料を供給すると、燃料の透過量が増加することがある。透過した燃料がカソード、より具体的にはカソード触媒上に存在すると、カソード触媒上で酸化剤と燃料とが直接反応して副反応が生じることがあり、燃料電池の発電効率が低下する。これを防止するために、液体燃料の供給量の制御が可能な燃料提供システムを用いてもよい。 The amount of fuel supplied can be controlled by the concentration of fuel in the liquid fuel and the supply speed (flow rate). The amount of fuel required varies depending on the amount of current to be extracted. Therefore, it is preferable to control the amount of fuel supplied to the anode side in accordance with the amount of current to be extracted. If an excessive amount of fuel is supplied relative to the amount of current to be extracted, the amount of fuel permeation may increase. When the permeated fuel is present on the cathode, more specifically, on the cathode catalyst, the oxidant and the fuel may directly react on the cathode catalyst to cause a side reaction, thereby reducing the power generation efficiency of the fuel cell. In order to prevent this, a fuel providing system capable of controlling the supply amount of liquid fuel may be used.
　電解質は、水又は液体燃料に溶解でき、液体燃料電池反応においてイオン伝導体として機能する電解質であれば特に限定されない。例えば、アルカリ形液体燃料電池においてはアニオンがイオン伝導体として機能するため、水酸化カリウム、水酸化ナトリウム、水酸化カルシウム等の水酸化物イオン（ＯＨ-イオン）の解離が可能な電解質を用いることが好ましい。二酸化炭素との反応物である炭酸カリウムが水に溶解しやすく、析出しにくいことから、電解質としては水酸化カリウムが特に好ましい。ただし、水に溶解可能であって水に溶解したときにイオンを供給できるその他の無機塩、イオン液体等を電解質として用いることもできる。 The electrolyte is not particularly limited as long as it is an electrolyte that can be dissolved in water or liquid fuel and functions as an ionic conductor in the liquid fuel cell reaction. For example, in an alkaline liquid fuel cell, an anion functions as an ionic conductor, so use an electrolyte that can dissociate hydroxide ions (OH - ions) such as potassium hydroxide, sodium hydroxide, and calcium hydroxide. Is preferred. Since potassium carbonate, which is a reaction product with carbon dioxide, is easily dissolved in water and hardly precipitated, potassium hydroxide is particularly preferable as the electrolyte. However, other inorganic salts, ionic liquids, etc. that can be dissolved in water and can supply ions when dissolved in water can also be used as the electrolyte.
　液体燃料中の電解質の濃度は、特に限定されないが、例えば重量基準で０．５～４０％、特に１～２０％である。 The concentration of the electrolyte in the liquid fuel is not particularly limited, but is, for example, 0.5 to 40%, particularly 1 to 20% on a weight basis.
　本実施形態のＭＥＡが設置された液体燃料電池において、電解質がイオン伝導性を担う点に本実施形態の特徴があり、この点が一般に用いられる液体燃料電池との相違点である。一般に用いられる液体燃料電池では、隔膜にアニオン交換膜を用いており、このアニオン交換膜の有するアニオン交換基がイオン伝導性を担う。従って、アニオン交換基が劣化すると、液体燃料電池の性能が低下する。これに対し、アニオン交換基を有しない場合にもイオン伝導が可能である本実施形態のＭＥＡでは、アニオン交換基の劣化は考慮する必要がない。 In the liquid fuel cell in which the MEA of the present embodiment is installed, the feature of the present embodiment is that the electrolyte bears ionic conductivity, and this point is different from the generally used liquid fuel cell. In the liquid fuel cell generally used, an anion exchange membrane is used for the diaphragm, and the anion exchange group of the anion exchange membrane bears ion conductivity. Therefore, when the anion exchange group is deteriorated, the performance of the liquid fuel cell is lowered. On the other hand, in the MEA of the present embodiment that can conduct ions even without an anion exchange group, it is not necessary to consider the deterioration of the anion exchange group.
　また、アルカリ形液体燃料電池では、カソード触媒における反応に水が必要である。この水は通常、加湿器等の補機類を用いて電池外部から加湿している。一方、本実施形態のＭＥＡに備えられた液体燃料電池用隔膜は、親水性官能基を有し隔膜中に水を保持できる。本実施形態のＭＥＡにはアノード側から液体燃料が供給されるため、この液体燃料に含まれる水はカソード側へ隔膜を透過し、カソード触媒における反応に利用される。従って、本実施形態のＭＥＡを用いると、加湿のための補機類の省略が可能となり、液体燃料電池の小型化や単位容積当たりの発電容量の向上を図る上で有利である。 Also, in the alkaline liquid fuel cell, water is required for the reaction at the cathode catalyst. This water is usually humidified from the outside of the battery using auxiliary equipment such as a humidifier. On the other hand, the diaphragm for a liquid fuel cell provided in the MEA of this embodiment has a hydrophilic functional group and can hold water in the diaphragm. Since the liquid fuel is supplied from the anode side to the MEA of this embodiment, water contained in the liquid fuel permeates the diaphragm to the cathode side and is used for the reaction in the cathode catalyst. Therefore, use of the MEA of this embodiment makes it possible to omit auxiliary equipment for humidification, which is advantageous in reducing the size of the liquid fuel cell and improving the power generation capacity per unit volume.
　上記の液体燃料電池は、アノード側からカソード側へと隔膜を透過した燃料やカソード触媒上でこの燃料と酸化剤とが直接反応して生じた副生成物の排出を抑制する観点から、カソード側の出口から排出されるガスを処理する補機類を備えていてもよい。 From the viewpoint of suppressing the discharge of by-products generated by the direct reaction of this fuel and oxidant on the cathode catalyst or the fuel that has permeated the diaphragm from the anode side to the cathode side, the above liquid fuel cell It is also possible to provide auxiliary equipment for processing the gas discharged from the outlet.
　以下、ＭＥＡについて詳細を述べる。 The details of MEA are described below.
　本実施形態のＭＥＡでは、本発明の隔膜の表面に触媒層が配置されている。隔膜と触媒層とは、典型的には触媒インクのスプレー塗布等の加工工程を経て一体化されている。通常、触媒層は、アノード触媒層とカソード触媒層とを含んでいる。図１に、本実施形態のＭＥＡの一例を示す。図１に示すＭＥＡは、隔膜２とアノード触媒層３とカソード触媒層４とを備え、アノード触媒層３が隔膜の一方の主面に、カソード触媒層４が隔膜２の他方の主面にそれぞれ配置されている。 In the MEA of the present embodiment, a catalyst layer is disposed on the surface of the diaphragm of the present invention. The diaphragm and the catalyst layer are typically integrated through a processing step such as spray application of catalyst ink. Usually, the catalyst layer includes an anode catalyst layer and a cathode catalyst layer. FIG. 1 shows an example of the MEA of this embodiment. The MEA shown in FIG. 1 includes a diaphragm 2, an anode catalyst layer 3, and a cathode catalyst layer 4. The anode catalyst layer 3 is on one main surface of the diaphragm, and the cathode catalyst layer 4 is on the other main surface of the diaphragm 2, respectively. Has been placed.
　ＭＥＡの形成方法は、本発明の効果を阻害しない限り特に限定されない。例えば、触媒層を形成した隔膜とガス拡散層とを接合させるＣＣＭ（Ｃａｔａｌｙｓｔ　Ｃｏａｔｅｄ　ｏｎ　Ｍｅｍｂｒａｎｅ）法又はガス拡散層に直接塗布した触媒層と隔膜とを接合させるＣＣＳ（Ｃａｔａｌｙｓｔ　Ｃｏａｔｅｄ　ｏｎ　Ｓｕｂｓｔｒａｔｅ）法が挙げられ、短絡防止等の観点からはＣＣＳ法を用いることが好ましい。 The method for forming the MEA is not particularly limited as long as the effects of the present invention are not impaired. For example, the CCM (Catalyst Coated on Membrane) method for joining the diaphragm formed with the catalyst layer and the gas diffusion layer, or the CCS (Catalyst Coated on Substrate) method for joining the catalyst layer directly applied to the gas diffusion layer and the diaphragm. Therefore, it is preferable to use the CCS method from the viewpoint of short circuit prevention.
　触媒層としては、アルカリ形液体燃料電池に使用する公知のＭＥＡが備える触媒層を用いることができる。触媒は、酸形燃料電池とは異なり、必ずしも白金のような貴金属である必要はなく、例えば、ニッケル、コバルト、鉄等の卑金属を使用可能である。含まれる具体的な触媒等、触媒層の構成は、ＭＥＡのアノード側（アノード触媒層）とカソード側（カソード触媒層）とで異なっていても同一であってもよい。特にカソード触媒層は、透過した燃料との反応を抑制して発電効率の低下を防ぎ、副反応による部材劣化を防ぐ観点から、酸化還元反応を選択的に促進する触媒を選択することが望ましい。 As the catalyst layer, a catalyst layer provided in a known MEA used in an alkaline liquid fuel cell can be used. Unlike an acid fuel cell, the catalyst does not necessarily need to be a noble metal such as platinum. For example, a base metal such as nickel, cobalt, or iron can be used. The structure of the catalyst layer, such as the specific catalyst contained, may be different or the same on the anode side (anode catalyst layer) and cathode side (cathode catalyst layer) of the MEA. In particular, for the cathode catalyst layer, it is desirable to select a catalyst that selectively promotes the oxidation-reduction reaction from the viewpoint of suppressing a reaction with the permeated fuel to prevent a decrease in power generation efficiency and preventing member deterioration due to a side reaction.
　本実施形態のＭＥＡは、本発明の効果を阻害しない限り、隔膜及び触媒層以外の任意の部材を有することができる。 The MEA of the present embodiment can have any member other than the diaphragm and the catalyst layer as long as the effects of the present invention are not impaired.
　以下、ＭＥＡに備えられている隔膜について詳細を述べる。 Hereinafter, details of the diaphragm provided in the MEA will be described.
　本実施形態において、液体燃料電池用隔膜は、高分子多孔膜と、高分子多孔膜に導入されたグラフト鎖とを備え、グラフト鎖は親水性官能基を含む。 In this embodiment, the diaphragm for a liquid fuel cell includes a polymer porous membrane and a graft chain introduced into the polymer porous membrane, and the graft chain includes a hydrophilic functional group.
　本実施形態において、液体燃料電池用隔膜は、膜厚が５μｍ～１３０μｍの範囲にあることが好ましく、１０μｍ～７０μｍの範囲にあることがより好ましい。膜厚が薄くなりすぎると、膜強度が低下することがあり、膜の破損やピンホール等の欠陥が生じることがあり、酸化剤の圧力を保てないことがある。また、燃料の透過量及び水の透過量（透水量）が多くなることがある。膜厚が厚くなりすぎると、隔膜内での膜としての抵抗（膜抵抗）が高くなることがあり、透水量が少なくなることがある。透水量が少なくなると、カソード触媒における反応に必要な水が不足し、発電効率が低下することがある。アノード側からカソード側へ隔膜を透過した燃料の量が増え、カソード触媒上に燃料が存在すると、燃料と酸化剤とが直接反応する副反応が生じることがある。その結果、電池の発電効率が低下し、副反応によってカソード触媒等が劣化することがある。従って、適切な燃料の透過量を有する隔膜を得るために、隔膜の膜厚を選択することが好ましい。 In this embodiment, the liquid fuel cell membrane preferably has a thickness in the range of 5 μm to 130 μm, and more preferably in the range of 10 μm to 70 μm. If the film thickness becomes too thin, the film strength may decrease, and the film may be damaged or defects such as pinholes may occur, which may prevent the pressure of the oxidizing agent from being maintained. Further, the amount of fuel permeation and the amount of water permeation (water permeation amount) may increase. If the film thickness becomes too thick, the resistance (film resistance) as a film within the diaphragm may increase, and the water permeability may decrease. When the amount of water permeation decreases, water required for the reaction in the cathode catalyst may be insufficient, and power generation efficiency may be reduced. If the amount of fuel that has passed through the diaphragm from the anode side to the cathode side increases and the fuel is present on the cathode catalyst, a side reaction may occur in which the fuel and the oxidant react directly. As a result, the power generation efficiency of the battery decreases, and the cathode catalyst or the like may deteriorate due to side reactions. Therefore, in order to obtain a diaphragm having an appropriate fuel permeation amount, it is preferable to select a film thickness of the diaphragm.
　本実施形態の隔膜の含水率は、乾燥時の隔膜の重量に対し３０％以上であることが好ましく、４０％～１００％であることが好ましく、５０％～８０％であることがより好ましい。本実施形態の隔膜においては、隔膜の有する親水性官能基が水を保有することによって、多孔膜の孔が補填される。このような含水率を有することによって、本実施形態の隔膜は多孔膜を有しているにもかかわらず、液体燃料電池用隔膜として使用でき、電極間の短絡を防止することが可能となり、空気等の酸化剤の圧力に耐えることが可能となる。また、隔膜に保有された水がカソード側へ透過するため、カソード触媒へ効率よく水を供給でき、電池の発電効率の向上に寄与できる。含水率が小さすぎると、多孔膜の孔は充分に補填されず、空気等の酸化剤の圧力に耐えることができないことがある。含水率が多くなりすぎると、空気等の気体に対する隔膜の耐圧性が低下し、酸化剤の圧力を保てないことがある。なお、乾燥時の隔膜とは、２３℃相対湿度５０％の雰囲気下に２４時間以上放置して寸法変化が生じなくなった状態の隔膜であり、含水時の隔膜とは、乾燥時の隔膜を３０℃の水中に２時間浸漬して膨潤させた状態の隔膜である。 The water content of the diaphragm of the present embodiment is preferably 30% or more, preferably 40% to 100%, more preferably 50% to 80% with respect to the weight of the diaphragm at the time of drying. In the diaphragm of the present embodiment, the hydrophilic functional group of the diaphragm retains water, so that the pores of the porous film are compensated. By having such a moisture content, the diaphragm of the present embodiment can be used as a diaphragm for a liquid fuel cell even though it has a porous film, and it is possible to prevent a short circuit between the electrodes. It is possible to withstand the pressure of an oxidizing agent such as Moreover, since the water retained in the diaphragm permeates to the cathode side, water can be efficiently supplied to the cathode catalyst, which can contribute to the improvement of the power generation efficiency of the battery. If the moisture content is too small, the pores of the porous membrane may not be sufficiently filled and may not be able to withstand the pressure of an oxidizing agent such as air. If the water content is too high, the pressure resistance of the diaphragm against a gas such as air may be reduced, and the pressure of the oxidant may not be maintained. In addition, the diaphragm at the time of drying is a diaphragm in a state in which dimensional change does not occur after being left in an atmosphere of 23 ° C. and 50% relative humidity for 24 hours or more. It is a diaphragm in a state of being swollen by being immersed in water at 2 ° C. for 2 hours.
　含水率は、具体的には以下の方法を用いて測定することができる。縦３０ｍｍ横２０ｍｍの矩形に切り出したサンプルを、２３℃相対湿度５０％の雰囲気下に２４時間以上放置して寸法変化が生じなくなった状態のサンプル重量を測定する（含水前の重量）。その後、このサンプルを３０℃の純水中に２時間浸漬した後、重量を測定する（含水後の重量）。なお、含水後の重量は、サンプル表面に付着した余剰な水を濾紙等で拭き取ってから測定する。含水率は、以下の式に基づいて計算した比率である。
　含水率（％）＝（（含水後の重量）－（含水前の重量））×１００／（含水前の重量） Specifically, the moisture content can be measured using the following method. A sample cut into a rectangular shape having a length of 30 mm and a width of 20 mm is left in an atmosphere at 23 ° C. and a relative humidity of 50% for 24 hours or more, and the weight of the sample in which no dimensional change occurs is measured (weight before water inclusion). Then, after immersing this sample in 30 degreeC pure water for 2 hours, a weight is measured (weight after water-containing). In addition, the weight after moisture is measured after wiping off excess water adhering to the sample surface with a filter paper or the like. The moisture content is a ratio calculated based on the following formula.
Moisture content (%) = ((weight after hydration) − (weight before hydration)) × 100 / (weight before hydration)
　本実施形態の隔膜は、面積膨潤率が抑制され、寸法安定性が良好である。面積膨潤率は２０％未満であることが好ましく、１５％以下であることがより好ましく、０％～１０％であることがさらに好ましく、０％～５％であることが特に好ましい。面積膨潤率が大きくなりすぎると、隔膜の変形が生じることがあり、隔膜の劣化につながる。また、面積膨潤率が大きくなりすぎると、本実施形態の隔膜を備えた液体燃料電池において、隔膜と燃料電池作動時の電極との接合性が劣ることがある。 The diaphragm of this embodiment has a reduced area swelling rate and good dimensional stability. The area swelling ratio is preferably less than 20%, more preferably 15% or less, further preferably 0% to 10%, and particularly preferably 0% to 5%. If the area swelling rate becomes too large, the diaphragm may be deformed, leading to deterioration of the diaphragm. Moreover, when the area swelling rate becomes too large, in the liquid fuel cell provided with the diaphragm of the present embodiment, the bondability between the diaphragm and the electrode during operation of the fuel cell may be inferior.
　面積膨潤率は、具体的には以下の方法を用いて測定することができる。縦３０ｍｍ横２０ｍｍの矩形に切り出したサンプルを、２３℃相対湿度５０％の雰囲気下に２４時間以上放置して寸法変化が生じなくなった状態のサンプルの面積を測定する（含水前の面積）。その後、このサンプルを３０℃の純水中に２時間浸漬した後、面積を測定する（含水後の面積）。面積膨潤率は、以下の式に基づいて計算した比率である。
面積膨潤率（％）＝（（含水後の面積）－（含水前の面積））×１００／（含水前の面積） Specifically, the area swelling rate can be measured using the following method. A sample cut into a rectangular shape having a length of 30 mm and a width of 20 mm is left in an atmosphere of 23 ° C. and 50% relative humidity for 24 hours or more, and the area of the sample in which no dimensional change occurs is measured (area before water inclusion). Then, after immersing this sample in 30 degreeC pure water for 2 hours, an area is measured (area after water inclusion). The area swelling rate is a ratio calculated based on the following formula.
Area swelling rate (%) = ((area after water inclusion) − (area before water inclusion)) × 100 / (area before water inclusion)
　ところで、アニオンの移動を利用した液体燃料電池（アルカリ形液体燃料電池）において、アノード側には燃料が、カソード側には空気等の酸化剤が供給される。アルカリ形液体燃料電池では、カソード側での反応には酸化剤の他に水が必要である。一般に、この水は、加湿器等の補機類を用いて外部から加湿して供給される。しかし、燃料電池の小型化、単位容積当たりの発電容量の向上等の観点から、補機類は可能な限り省略することが望ましい。補機類を省略するためには、アノード側に燃料と共に供給され、カソード側へと隔膜を透過する水を利用することが考えられる。この場合、良好に水を透過することができる隔膜を使用することが望まれる。 By the way, in a liquid fuel cell (alkaline liquid fuel cell) utilizing the movement of anions, fuel is supplied to the anode side and an oxidant such as air is supplied to the cathode side. In the alkaline liquid fuel cell, the reaction on the cathode side requires water in addition to the oxidant. In general, this water is supplied by being humidified from the outside using an auxiliary device such as a humidifier. However, it is desirable to omit auxiliary equipment as much as possible from the viewpoint of miniaturization of the fuel cell and improvement of power generation capacity per unit volume. In order to omit the auxiliary machinery, it is conceivable to use water supplied together with fuel to the anode side and permeating the diaphragm to the cathode side. In this case, it is desired to use a diaphragm that can permeate water well.
　気体を燃料とする燃料電池と同様、液体燃料電池にも、隔膜と触媒層とが一体化した膜－電極接合体（ＭＥＡ）が備えられる。液体燃料電池の安定した発電効率等の観点から、隔膜と触媒層との界面における剥離が生じにくいことが求められる。触媒層との界面における隔膜の変形が、この剥離の一因となり得るため、隔膜には良好な寸法安定性が求められる。 Like a fuel cell using gas as a fuel, a liquid fuel cell includes a membrane-electrode assembly (MEA) in which a diaphragm and a catalyst layer are integrated. From the viewpoint of the stable power generation efficiency of the liquid fuel cell, it is required that separation at the interface between the diaphragm and the catalyst layer hardly occurs. Since deformation of the diaphragm at the interface with the catalyst layer can contribute to this separation, the diaphragm is required to have good dimensional stability.
　本発明者等は、カソード側に良好に水を供給できる隔膜について検討を行った。その結果、含水率が特定の値以上の隔膜を用いることによって、カソード側へ安定して水を供給できることが見出された。 The present inventors examined a diaphragm that can supply water to the cathode side satisfactorily. As a result, it was found that water can be stably supplied to the cathode side by using a diaphragm having a moisture content of a specific value or more.
　一方で、ＭＥＡにおける隔膜と触媒層との剥離を抑制するためには、良好な寸法安定性を有する隔膜、特に隔膜と触媒層との界面（隔膜の面積方向）における良好な寸法安定性を有することが好ましい。本発明者等の検討により、特定の範囲の面積膨潤率を有する隔膜を用いることによって、ＭＥＡにおける隔膜と触媒層との剥離を抑制できることが見出された。 On the other hand, in order to suppress the separation between the diaphragm and the catalyst layer in the MEA, the diaphragm has a good dimensional stability, particularly, has a good dimensional stability at the interface between the diaphragm and the catalyst layer (area direction of the diaphragm). It is preferable. As a result of studies by the present inventors, it has been found that the separation of the membrane and the catalyst layer in the MEA can be suppressed by using a membrane having an area swelling ratio in a specific range.
　すなわち本発明は、別の側面から、
　乾燥時の隔膜の重量に対する、含水時の隔膜の重量と乾燥時の隔膜の重量との重量差の比率が３０重量％以上であり、
　乾燥時の隔膜の面積に対する、含水時の隔膜の面積と乾燥時の隔膜の面積との面積差の比率が２０％未満である、
　液体燃料電池用隔膜、を提供する。液体燃料電池は、アルカリ形であることが好ましい。 That is, the present invention from another aspect,
The ratio of the weight difference between the weight of the diaphragm when wet and the weight of the diaphragm when dried to the weight of the diaphragm when dried is 30% by weight or more,
The ratio of the area difference between the area of the diaphragm when wet and the area of the diaphragm when dried to the area of the diaphragm when dried is less than 20%.
A diaphragm for a liquid fuel cell is provided. The liquid fuel cell is preferably in alkaline form.
　この側面によれば、本発明は、液体燃料電池の特性の向上に寄与できる液体燃料電池用隔膜を提供することができる。 According to this aspect, the present invention can provide a diaphragm for a liquid fuel cell that can contribute to improving the characteristics of the liquid fuel cell.
　一般に、乾燥状態の隔膜は、吸水すると膨潤する。従って、良好な含水率と良好な寸法安定性（抑制された膨潤率）とを共に備えた隔膜を得ることは困難であった。これに対し、この隔膜の含水率は良好であり、隔膜の面積方向の膨潤が抑制されている。 Generally, a dry diaphragm swells when it absorbs water. Therefore, it has been difficult to obtain a diaphragm having both a good moisture content and a good dimensional stability (suppressed swelling rate). On the other hand, the moisture content of the diaphragm is good, and swelling in the area direction of the diaphragm is suppressed.
　この隔膜は、親水性官能基を有する多孔膜であることが好ましい。隔膜は、多孔膜と多孔膜上に存在する親水性官能基とを備えることが好ましい。多孔膜としては、例えば無機基材からなる多孔膜、高分子基材からなる多孔膜が挙げられる。 This diaphragm is preferably a porous film having a hydrophilic functional group. The diaphragm preferably comprises a porous membrane and a hydrophilic functional group present on the porous membrane. Examples of the porous film include a porous film made of an inorganic base material and a porous film made of a polymer base material.
　本実施形態の隔膜は、断面方向の透水速度が４０ｍｏｌ/ｈ・ｇ以上にあることが好ましく、４０～１２０ｍｏｌ/ｈ・ｇにあることがより好ましく、５０～１１０ｍｏｌ/ｈ・ｇにあることがさらに好ましい。隔膜の断面方向の透水速度が小さくなりすぎると、カソード触媒上での反応に必要な水が充分に透過せず、カソード触媒における反応の効率が低下することがある。断面方向の透水速度が特定の範囲にある本実施形態の隔膜を用いることによって、アノード側からカソード側へと隔膜を透過した水を、カソード触媒に適切に供給できる。その結果、カソード触媒上での反応効率の向上に寄与でき、さらに電池の発電効率の向上に寄与できる。 In the diaphragm of the present embodiment, the water transmission rate in the cross-sectional direction is preferably 40 mol / h · g or more, more preferably 40 to 120 mol / h · g, and more preferably 50 to 110 mol / h · g. Further preferred. If the water permeation rate in the cross-sectional direction of the diaphragm becomes too small, water necessary for the reaction on the cathode catalyst may not permeate sufficiently, and the reaction efficiency in the cathode catalyst may be reduced. By using the diaphragm of the present embodiment in which the water permeation speed in the cross-sectional direction is in a specific range, water that has permeated the diaphragm from the anode side to the cathode side can be appropriately supplied to the cathode catalyst. As a result, the reaction efficiency on the cathode catalyst can be improved, and the power generation efficiency of the battery can be further improved.
　隔膜の断面方向の透水速度は、具体的には、図２～４に示す評価用セル１００を用いて以下の方法により測定することができる。 Specifically, the water transmission rate in the cross-sectional direction of the diaphragm can be measured by the following method using the evaluation cell 100 shown in FIGS.
　第一主面及び第一主面と反対側の第二主面を有する隔膜２を準備し、一辺の長さが２ｃｍの正方形の開口部１１ａ、２１ａを有する、一対のガスケット１１、２１で隔膜２を挟持する。ガスケット１１、２１の外側に、サーペンタイン構造の流路１２ａ、２２ａ付きの一対のセパレータ１２、２２、一対の集電板１３、２３、一対のエンドプレート１４、２４をこの順に配置して隔膜２を挟持する。部材の各接触面から空気、水が漏洩しないように、ボルト等の固定部品（図示せず）を用いて各部材を締結し、評価用セル１００を形成する。 A diaphragm 2 having a first main surface and a second main surface opposite to the first main surface is prepared, and a diaphragm is formed by a pair of gaskets 11 and 21 having square openings 11a and 21a each having a side length of 2 cm. 2 is pinched. On the outside of the gaskets 11 and 21, a pair of separators 12 and 22 with serpentine-structured flow channels 12a and 22a, a pair of current collector plates 13 and 23, and a pair of end plates 14 and 24 are arranged in this order to form the diaphragm 2 Hold it. Each member is fastened using a fixing part (not shown) such as a bolt so that air and water do not leak from each contact surface of the member, and the evaluation cell 100 is formed.
　評価用セル１００は、流路１８、１９、２８、２９を有する。流路１８、１９はそれぞれ水の供給、吐出用の流路であり、流路２８、２９はそれぞれ乾燥空気の供給、吐出用の流路である。各流路１８、１９、２８、２９はエンドプレートに開口を有する。流路１８、１９はエンドプレート１４、集電板１３及びセパレータ１２を貫通し、流路１２ａと連結する。 The evaluation cell 100 has flow paths 18, 19, 28, and 29. The channels 18 and 19 are channels for supplying and discharging water, respectively, and the channels 28 and 29 are channels for supplying and discharging dry air, respectively. Each flow path 18, 19, 28, 29 has an opening in the end plate. The flow paths 18 and 19 penetrate the end plate 14, the current collector plate 13, and the separator 12, and are connected to the flow path 12a.
　隔膜２の第一主面及び第二主面が鉛直方向に沿うように評価用セル１００を設置し、この状態の評価用セル１００に水及び乾燥空気の供給を開始する。第一主面へは毎分２ｍｌの水を流路１８に接続した配管３８を介して供給し、第二主面へは毎分５００ｍｌの乾燥空気を流路２８に接続した配管４８を介して供給する。上記のように水を供給し続けることによって、セル１００の第一主面側の内部は供給された水で満たされ、隔膜２の第一主面は常に水と接触する。この際、エンドプレート１４、２４に設けたラバーヒーター１５、２５を用いて評価用セル１００の温度が８０℃になるように評価用セル１００を加熱する。水及び乾燥空気を上記のように供給し続け、評価用セル１００の温度を８０℃に維持しながら、流路１９に接続した配管３９から排出される水を３０分間回収する（Ｗ２）。 The evaluation cell 100 is installed so that the first main surface and the second main surface of the diaphragm 2 are along the vertical direction, and supply of water and dry air to the evaluation cell 100 in this state is started. 2 ml of water per minute is supplied to the first main surface via a pipe 38 connected to the flow path 18, and 500 ml of dry air per minute is supplied to the second main face via a pipe 48 connected to the flow path 28. Supply. By continuing to supply water as described above, the inside of the first main surface side of the cell 100 is filled with the supplied water, and the first main surface of the diaphragm 2 is always in contact with water. At this time, the evaluation cell 100 is heated using the rubber heaters 15 and 25 provided on the end plates 14 and 24 so that the temperature of the evaluation cell 100 becomes 80 ° C. Water and dry air are continuously supplied as described above, and water discharged from the pipe 39 connected to the flow path 19 is collected for 30 minutes while maintaining the temperature of the evaluation cell 100 at 80 ° C. (W2).
　Ｗ１は、評価セル１００へ３０分間供給した水の重量であり、Ｗ２は、配管３９から排出される水を３０分間回収した水の重量である。また、Ｗ３は、隔膜２とは別に準備した隔膜２と同一種類のＷ３測定用隔膜を、２３℃相対湿度５５％雰囲気下で２４時間放静置後測定した重量から計算した、隔膜の１ｃｍ2あたりの重量である。隔膜の断面方向の透水速度は、これらの値を用いて、以下の式によって計算される値である。
隔膜の断面方向の透水速度［ｍｏｌ/ｈ・ｇ］＝６０［分］/３０［分］×（Ｗ１－Ｗ２）［ｇ］/１８［ｇ/ｍｏｌ］/４［ｃｍ2］/Ｗ３［ｇ/ｃｍ2］ W1 is the weight of water supplied to the evaluation cell 100 for 30 minutes, and W2 is the weight of water recovered from the pipe 39 for 30 minutes. Also, W3 is the W3 measuring diaphragm of the same type and the membrane 2 was prepared separately from the diaphragm 2, were calculated from the weight measured 24 hours Hosei after standing in an atmosphere 23 ° C. relative humidity 55%, 1 cm of the membrane 2 It is per weight. The water transmission rate in the cross-sectional direction of the diaphragm is a value calculated by the following formula using these values.
Water permeability rate [mol / h · g] = 60 [min] / 30 [min] × (W1-W2) [g] / 18 [g / mol] / 4 [cm 2 ] / W3 [g / cm 2 ]
　本実施形態の隔膜の第一主面に水を供給しながら、第一主面と反対側の第二主面に空気を供給して、空気の圧力を上昇させて測定した主面間耐圧（隔膜の主面間耐圧）は、６０ｋＰａ以上であることが好ましく、８０ｋＰａ以上であることがより好ましく、１００ｋＰａ以上であることがさらに好ましい。隔膜の主面間耐圧とは、隔膜が維持できる主面間の圧力の最大値である。隔膜の主面間耐圧が小さくなりすぎると、気体である酸化剤の圧力を保てないことがあり、酸化剤がアノードへリークすることがある。酸化剤がアノードへリークし、燃料と酸化剤とが直接混合すると、発電効率が低下することがある。 While supplying water to the first main surface of the diaphragm of the present embodiment, air is supplied to the second main surface opposite to the first main surface, and the pressure between the main surfaces measured by increasing the pressure of the air ( The pressure resistance between the main surfaces of the diaphragm is preferably 60 kPa or more, more preferably 80 kPa or more, and further preferably 100 kPa or more. The pressure resistance between the main surfaces of the diaphragm is the maximum value of the pressure between the main surfaces that can maintain the diaphragm. If the pressure resistance between the main surfaces of the diaphragm is too small, the pressure of the oxidizing agent that is a gas may not be maintained, and the oxidizing agent may leak to the anode. If the oxidant leaks to the anode and the fuel and the oxidant are mixed directly, the power generation efficiency may be reduced.
　隔膜の主面間耐圧は、具体的には図２～４に示す評価用セル１００を用いて以下の方法により測定することができる。この評価用セル１００は、上述した隔膜の断面方向の透水速度の測定に用いる評価用セル１００と同様に形成する。 Specifically, the pressure resistance between the main surfaces of the diaphragm can be measured by the following method using the evaluation cell 100 shown in FIGS. This evaluation cell 100 is formed in the same manner as the evaluation cell 100 used for the measurement of the water transmission rate in the cross-sectional direction of the diaphragm described above.
　隔膜２の第一主面及び第二主面が鉛直方向に沿うように評価用セル１００を設置し、この状態の評価用セル１００に水及び乾燥空気の供給を開始する。第一主面へは毎分２ｍｌの水を流路１８に接続した配管３８を介して供給し、第二主面へは毎分５００ｍｌの乾燥空気を流路２８に接続した配管４８を介して供給する。上記のように水を供給し続けることによって、セル１００の第一主面側の内部は供給された水で満たされ、隔膜２の第一主面は常に水と接触する。この際、エンドプレート１４、２４に設けたラバーヒーター１５、２５を用いて評価用セル１００の温度が８０℃になるように評価用セル１００を加熱する。 The evaluation cell 100 is installed so that the first main surface and the second main surface of the diaphragm 2 are along the vertical direction, and supply of water and dry air to the evaluation cell 100 in this state is started. 2 ml of water per minute is supplied to the first main surface via a pipe 38 connected to the flow path 18, and 500 ml of dry air per minute is supplied to the second main face via a pipe 48 connected to the flow path 28. Supply. By continuing to supply water as described above, the inside of the first main surface side of the cell 100 is filled with the supplied water, and the first main surface of the diaphragm 2 is always in contact with water. At this time, the evaluation cell 100 is heated using the rubber heaters 15 and 25 provided on the end plates 14 and 24 so that the temperature of the evaluation cell 100 becomes 80 ° C.
　次に、水及び乾燥空気を上記のように供給し続け、評価用セル１００の温度を８０℃に維持しながら、流路２９に接続した配管４９に設けた圧力調整装置４３（例えば、バルブ）の開度を調整し、隔膜２の第二主面への乾燥空気の圧力が２０ｋＰａになるように、第二主面への乾燥空気の圧力を昇圧する。乾燥空気の圧力は配管４９に設けた圧力計４２で測定する。その後、水及び乾燥空気を上記のように供給し続け、評価用セル１００の温度を８０℃に維持しながら、第二主面への乾燥空気の圧力を２０ｋＰａに維持できるように圧力調整装置４３の開度を調整する。上記の水及び乾燥空気の供給速度、評価用セル１００の温度、圧力調整装置４３の開度を維持した状態で、第二主面への乾燥空気の圧力を１０分間測定する。２０ｋＰａを１０分間維持できなかった場合には、隔膜の主面間耐圧は０ｋＰａと評価する。２０ｋＰａを１０分間維持できた場合には、第二主面への乾燥空気の圧力を昇圧し、４０ｋＰａ、６０ｋＰａ、８０ｋＰａ、１００ｋＰａの順に同様の測定を行う。第二主面への乾燥空気の圧力を１００ｋＰａに昇圧後１０分間維持できた場合には、隔膜の主面間耐圧は１００ｋＰａとする。ここで、圧力を維持できた場合とは、第二主面への乾燥空気の圧力の変化が、１０分間において１ｋＰａ以下であることをいう。 Next, the pressure adjusting device 43 (for example, a valve) provided in the pipe 49 connected to the flow path 29 while maintaining the temperature of the evaluation cell 100 at 80 ° C. while continuing to supply water and dry air as described above. And the pressure of the dry air to the second main surface is increased so that the pressure of the dry air to the second main surface of the diaphragm 2 is 20 kPa. The pressure of the dry air is measured with a pressure gauge 42 provided in the pipe 49. Thereafter, the pressure regulator 43 continues to supply water and dry air as described above, and maintains the temperature of the evaluation cell 100 at 80 ° C. so that the pressure of the dry air to the second main surface can be maintained at 20 kPa. Adjust the opening. The pressure of the dry air to the second main surface is measured for 10 minutes while maintaining the supply rate of water and dry air, the temperature of the evaluation cell 100, and the opening degree of the pressure adjusting device 43. When 20 kPa cannot be maintained for 10 minutes, the withstand pressure between the main surfaces of the diaphragm is evaluated as 0 kPa. When 20 kPa can be maintained for 10 minutes, the pressure of the dry air to the second main surface is increased, and the same measurement is performed in the order of 40 kPa, 60 kPa, 80 kPa, and 100 kPa. When the pressure of the dry air to the second main surface can be maintained for 10 minutes after increasing the pressure to 100 kPa, the pressure resistance between the main surfaces of the diaphragm is set to 100 kPa. Here, the case where the pressure can be maintained means that the change in the pressure of the dry air to the second main surface is 1 kPa or less in 10 minutes.
　ところで、アニオンの移動を利用した液体燃料電池（アルカリ形液体燃料電池）において、アノード側には燃料が、カソード側には空気等の酸化剤が供給される。カソード側での反応には酸化剤の他に水が必要である。一般に、この水は、加湿器等の補機類を用いて外部から加湿して供給される。しかし、燃料電池の小型化、単位容積当たりの発電容量の向上等の観点から、補機類は可能な限り省略することが望ましい。補機類を省略するためには、アノード側に燃料と共に供給され、カソード側へと隔膜を透過する水を利用することが考えられる。この場合、良好に水を透過することができる隔膜を使用することが望まれる。 By the way, in a liquid fuel cell (alkaline liquid fuel cell) utilizing the movement of anions, fuel is supplied to the anode side and an oxidant such as air is supplied to the cathode side. The reaction on the cathode side requires water in addition to the oxidizing agent. In general, this water is supplied by being humidified from the outside using an auxiliary device such as a humidifier. However, it is desirable to omit auxiliary equipment as much as possible from the viewpoint of miniaturization of the fuel cell and improvement of power generation capacity per unit volume. In order to omit the auxiliary machinery, it is conceivable to use water supplied together with fuel to the anode side and permeating the diaphragm to the cathode side. In this case, it is desired to use a diaphragm that can permeate water well.
　一方、酸化剤と燃料が直接混合すると副反応が生じ、発電効率が低下する。隔膜には、酸化剤と燃料とを隔離する機能も求められる。酸化剤としては、空気等の気体が用いられるため、隔膜には気体に対する良好な耐圧性が必要となる。 On the other hand, if the oxidant and fuel are mixed directly, side reactions occur and power generation efficiency decreases. The diaphragm is also required to have a function of separating the oxidant and the fuel. Since a gas such as air is used as the oxidizing agent, the diaphragm needs to have good pressure resistance against the gas.
　従って、本発明は、また別の側面から、
　断面方向の透水速度が４０ｍｏｌ/ｈ・ｇ以上であり、
　かつ第一主面に水を供給しながら、前記第一主面と反対側の第二主面に空気を供給して、前記空気の圧力を上昇させて測定した主面間耐圧が８０ｋＰａ以上である、
　液体燃料電池用隔膜、を提供する。液体燃料電池は、アルカリ形であることが好ましい。 Therefore, the present invention from another aspect,
The water transmission rate in the cross-sectional direction is 40 mol / h · g or more,
And while supplying water to the first main surface, air is supplied to the second main surface opposite to the first main surface and the pressure between the main surfaces measured by increasing the pressure of the air is 80 kPa or more. is there,
A diaphragm for a liquid fuel cell is provided. The liquid fuel cell is preferably in alkaline form.
　この側面によれば、本発明は、液体燃料電池、特にアルカリ形液体燃料電池に適した新たな液体燃料電池用隔膜を提供することができる。 According to this aspect, the present invention can provide a new diaphragm for a liquid fuel cell suitable for a liquid fuel cell, particularly an alkaline liquid fuel cell.
　この隔膜は、高分子基材と、高分子基材上に存在する親水性官能基とを備えていてもよい。高分子基材の材質としては、高分子多孔膜の材質として後述するものを用いることができる。高分子基材は、多孔膜（高分子多孔膜）であってもよい。高分子基材上に存在する親水性官能基は、親水化処理を実施することによって得られることが好ましい。例えば、液体燃料電池用隔膜は、高分子多孔膜を準備する工程と、その高分子多孔膜に親水化処理を実施する工程と、を経ることによって形成することができる。 The diaphragm may include a polymer base material and a hydrophilic functional group present on the polymer base material. As the material for the polymer substrate, those described later as the material for the polymer porous membrane can be used. The polymer substrate may be a porous membrane (polymer porous membrane). The hydrophilic functional group present on the polymer substrate is preferably obtained by carrying out a hydrophilic treatment. For example, the diaphragm for a liquid fuel cell can be formed through a step of preparing a polymer porous membrane and a step of hydrophilizing the polymer porous membrane.
　親水化処理の種類は特に限定されず、グラフト重合処理、コロナ処理、プラズマ処理、スパッタ処理、スルホン化処理、界面活性剤又は親水性ポリマーを用いた処理等を用いてもよい。 The type of hydrophilic treatment is not particularly limited, and graft polymerization treatment, corona treatment, plasma treatment, sputtering treatment, sulfonation treatment, treatment using a surfactant or a hydrophilic polymer, and the like may be used.
　親水性ポリマーを用いた処理においては、親水性ポリマーを含む溶液を高分子多孔膜に塗工し、高分子多孔膜の表面及び細孔壁に親水性ポリマー膜を形成することによって、多孔膜の表面に親水性官能基を付加してもよい。この方法では、親水性ポリマーを塗布して形成された膜の厚みによって、親水性官能基の量を調整することができ、また膜の厚みによって被膜中の隔膜の平均孔径の調整が可能となる。 In the treatment using the hydrophilic polymer, a solution containing the hydrophilic polymer is applied to the polymer porous membrane, and the hydrophilic polymer membrane is formed on the surface and pore walls of the polymer porous membrane, thereby A hydrophilic functional group may be added to the surface. In this method, the amount of the hydrophilic functional group can be adjusted by the thickness of the film formed by applying the hydrophilic polymer, and the average pore diameter of the diaphragm in the film can be adjusted by the thickness of the film. .
　親水化処理は、均一系で処理できる観点から、グラフト重合法を用いて実施されることが好ましい。液体燃料電池用隔膜は、高分子基材と、高分子基材に導入されたグラフト鎖とを備え、グラフト鎖は親水性官能基を有することが好ましい。 The hydrophilization treatment is preferably performed using a graft polymerization method from the viewpoint that it can be treated in a uniform system. The diaphragm for a liquid fuel cell includes a polymer substrate and a graft chain introduced into the polymer substrate, and the graft chain preferably has a hydrophilic functional group.
　本実施形態の隔膜の透気度（ガーレー値）は、１００～２０００ｓｅｃ／１００ｍｌ・ｉｎｃｈ2の範囲にあることが好ましく、２００～１０００ｓｅｃ／１００ｍｌ・ｉｎｃｈ2の範囲にあることがより好ましい。透気度が大きくなりすぎると、透水量、透水速度が低下することがある。その結果、カソード触媒における反応に必要な水が不足し、カソード触媒での反応効率が低下することがある。 Air permeability of the membrane of the present embodiment (Gurley value) is preferably in the range of 100 ~ 2000sec / 100ml · inch 2 , more preferably in the range of 200 ~ 1000sec / 100ml · inch 2 . If the air permeability becomes too large, the amount of water permeation and the water permeation rate may decrease. As a result, water required for the reaction at the cathode catalyst may be insufficient, and the reaction efficiency at the cathode catalyst may be reduced.
　本実施形態の隔膜は、メタノール保液率が２０％以上であることが好ましい。ここで、隔膜のメタノール保液率とは、予め長辺５０ｍｍ短辺１０ｍｍの矩形に切り出し、２３℃相対湿度５０％の雰囲気下に１２時間以上静置した隔膜を試験片とし、２３℃相対湿度５０％の雰囲気下でメタノールの液面に対して矩形の長辺が垂直になるとともに試験片の底部から５ｍｍの部分がメタノール中に浸漬する状態でメタノールに対して試験片を保持し、この状態を１分間維持した後の液面からの吸液高さの長辺に対する比率である。 The diaphragm of the present embodiment preferably has a methanol retention rate of 20% or more. Here, the methanol liquid retention rate of the diaphragm is a 23-degree relative humidity measured by using a diaphragm that was previously cut into a rectangle having a long side of 50 mm and a short side of 10 mm and left standing in an atmosphere of 23 ° C. and 50% relative humidity for 12 hours or more. In a 50% atmosphere, the long side of the rectangle is perpendicular to the liquid level of methanol, and the test piece is held against methanol in a state where the portion 5 mm from the bottom of the test piece is immersed in methanol. Is the ratio of the liquid absorption height from the liquid surface to the long side after maintaining for 1 minute.
　本発明では、隔膜の有する燃料液の保液率を評価するために、隔膜のメタノールの保持率（メタノール保液率）を測定している。燃料液は、具体的には、燃料を水に溶解した燃料水溶液であり、電解質を溶解している。メタノールは、水に溶解させて燃料溶液として液体燃料電池に供給することができる。さらに、メタノールは、燃料溶液に用いる水と、その構造及び分子量が相対的に類似している。従って、メタノール保液率を測定することによって、隔膜の有する燃料液の保持率を評価する妥当な結果が得られると考えられる。 In the present invention, in order to evaluate the liquid retention rate of the fuel liquid that the diaphragm has, the methanol retention rate (methanol retention rate) of the diaphragm is measured. Specifically, the fuel liquid is an aqueous fuel solution in which fuel is dissolved in water, and dissolves an electrolyte. Methanol can be dissolved in water and supplied to the liquid fuel cell as a fuel solution. Furthermore, methanol is relatively similar in structure and molecular weight to water used in fuel solutions. Therefore, it is considered that an appropriate result for evaluating the fuel liquid retention rate of the diaphragm can be obtained by measuring the methanol liquid retention rate.
　燃料液を保液できる隔膜は、燃料液に溶解された電解質を燃料液とともに保持することができる。この電解質が燃料電池におけるイオン伝導性を担うため、メタノール保液率の良好な隔膜を用いるとイオン伝導性が良好になり、発電時の燃料電池における電気抵抗を抑制することができる。隔膜に含まれる電解質の量が少なすぎると、発電できない場合があり、発電できた場合でも発電時の燃料電池における電気抵抗が大きくなることがある。上記の範囲のメタノール保液率を有する隔膜は、燃料液に含まれる水を良好に保持することができる。この水がカソード側に透過するため、メタノール保液率の良好な隔膜を用いるとカソード触媒に水を良好に供給できると考えられる。従って、本実施形態の隔膜を用いるとカソード触媒へ水を供給するための加湿器等の補機類は必須でない。一方、隔膜のメタノール保液率が低すぎると、隔膜の有する細孔に充分に燃料液が補填されない。このような隔膜は、カソード側に供給される酸化剤の圧力を保てず、酸化剤が隔膜を通じてアノード側へリークすることがある。このように本実施形態の隔膜は、カソードにおける酸素還元反応の効率の向上に寄与でき、電池の発電効率の向上に寄与し得る。 The diaphragm capable of retaining the fuel liquid can hold the electrolyte dissolved in the fuel liquid together with the fuel liquid. Since this electrolyte is responsible for ionic conductivity in the fuel cell, the use of a diaphragm having a good methanol retention rate improves the ionic conductivity and suppresses the electrical resistance in the fuel cell during power generation. If the amount of electrolyte contained in the diaphragm is too small, power generation may not be possible, and even when power generation is possible, the electrical resistance of the fuel cell during power generation may increase. A diaphragm having a methanol liquid retention rate in the above range can satisfactorily retain water contained in the fuel liquid. Since this water permeates to the cathode side, it is considered that water can be satisfactorily supplied to the cathode catalyst when a diaphragm having a good methanol retention rate is used. Therefore, when the diaphragm of the present embodiment is used, auxiliary equipment such as a humidifier for supplying water to the cathode catalyst is not essential. On the other hand, if the methanol retention rate of the diaphragm is too low, the fuel liquid is not sufficiently filled in the pores of the diaphragm. Such a diaphragm cannot maintain the pressure of the oxidant supplied to the cathode side, and the oxidant may leak to the anode side through the diaphragm. Thus, the diaphragm of this embodiment can contribute to the improvement of the efficiency of the oxygen reduction reaction at the cathode, and can contribute to the improvement of the power generation efficiency of the battery.
　ところで、アニオンの移動を利用した液体燃料電池（アルカリ形液体燃料電池）においては、アノード側には燃料が、カソード側には空気等の酸化剤が供給される。また、気体を燃料とする燃料電池と同様、液体燃料電池にも、隔膜と触媒層とが一体化した膜－電極接合体（ＭＥＡ）が備えられる。 By the way, in a liquid fuel cell (an alkaline liquid fuel cell) utilizing the movement of anions, fuel is supplied to the anode side and an oxidant such as air is supplied to the cathode side. Similarly to a fuel cell using gas as a fuel, a liquid fuel cell includes a membrane-electrode assembly (MEA) in which a diaphragm and a catalyst layer are integrated.
　アルカリ形液体燃料電池においては、カソードでの酸素還元反応に水が必要である。この水を供給するために、一般に加湿器等の補機類を用いて、電池の外部から酸化剤を加湿する手段がとられている。しかし、燃料電池の単位容積当たりの発電容量の向上、燃料電池システムの小型化及び軽量化、燃料電池システムの製造コストの低減の観点から、補機類は可能な限り省略されることが望ましい。補機類を省略するためには、アノード側からカソード側へと隔膜を透過した水を使用することが考えられる。この場合、良好に水を透過できる隔膜を使用することが考えられる。 In alkaline liquid fuel cells, water is required for the oxygen reduction reaction at the cathode. In order to supply this water, means for humidifying the oxidant from the outside of the battery is generally taken using auxiliary equipment such as a humidifier. However, it is desirable to omit auxiliary equipment as much as possible from the viewpoint of improving the power generation capacity per unit volume of the fuel cell, reducing the size and weight of the fuel cell system, and reducing the manufacturing cost of the fuel cell system. In order to omit the auxiliary machinery, it is conceivable to use water that has passed through the diaphragm from the anode side to the cathode side. In this case, it is conceivable to use a diaphragm that can penetrate water well.
　従って、本発明は、さらに別の側面から、
　メタノール保液率が２０％以上の多孔膜である、
　液体燃料電池用隔膜、を提供する。液体燃料電池は、アルカリ形であることが好ましい。 Therefore, the present invention from still another aspect,
It is a porous membrane having a methanol retention rate of 20% or more.
A diaphragm for a liquid fuel cell is provided. The liquid fuel cell is preferably in alkaline form.
　この側面によれば、本発明は、液体燃料電池の特性の向上に寄与できる液体燃料電池用隔膜を提供することができる。 According to this aspect, the present invention can provide a diaphragm for a liquid fuel cell that can contribute to improving the characteristics of the liquid fuel cell.
　この液体燃料電池用隔膜は、親水性官能基を備えることが好ましい。親水性官能基を備えることによって、メタノール保液性がより良好になりえる。親水性官能基は、イオン伝導性を促進できる観点からは、イオン伝導性を有する官能基であってもよい。 The liquid fuel cell membrane preferably has a hydrophilic functional group. By providing a hydrophilic functional group, the liquid retention of methanol can be improved. From the viewpoint of promoting ion conductivity, the hydrophilic functional group may be a functional group having ion conductivity.
　この多孔膜として、公知の多孔膜を用いることができる。例えば、無機基材からなる多孔膜、高分子基材からなる多孔膜が挙げられる。高分子基材からなる多孔膜は、例えば親水性官能基を有する重合性単量体を重合することによって形成できる。多孔膜が親水性官能基を備えていない場合には、親水化処理を実施して多孔膜の表面に親水性官能基を導入してもよい。 As this porous film, a known porous film can be used. Examples thereof include a porous film made of an inorganic base material and a porous film made of a polymer base material. A porous film made of a polymer substrate can be formed, for example, by polymerizing a polymerizable monomer having a hydrophilic functional group. When the porous membrane does not have a hydrophilic functional group, a hydrophilic functional group may be introduced on the surface of the porous membrane by performing a hydrophilic treatment.
　この燃料電池用隔膜は、第一主面に水を供給しながら、第一主面と反対側の第二主面に空気を供給して、空気の圧力を上昇させて測定した主面間耐圧（隔膜の主面間耐圧）が６０ｋＰａ以上であることが好ましく、８０ｋＰａ以上であることがより好ましく、１００ｋＰａ以上であることがさらに好ましい。 This fuel cell membrane is measured by increasing the air pressure by supplying air to the second main surface opposite to the first main surface while supplying water to the first main surface. The pressure resistance between the main surfaces of the diaphragm is preferably 60 kPa or more, more preferably 80 kPa or more, and further preferably 100 kPa or more.
　本実施形態の隔膜の重量は、高分子多孔膜の重量の１．０５～３．０倍（グラフト率５～２００％）の範囲にあることが好ましく、１．１５～２．０倍（グラフト率１５％～１００％）の範囲にあることがより好ましい。このようなグラフト率を有することにより、高分子多孔膜の含水率、保液率、透水性等が良好になりえる。グラフト率が低すぎると、充分な親水性を隔膜に付与できず、また含水時の多孔膜の耐圧性が得られないことがある。グラフト率が高くなりすぎると、隔膜の面積膨潤率が増加し、含水しすぎることで隔膜の物理的耐久性が低下する懸念がある。また、隔膜が膨張することによって孔が閉塞され、液体燃料に溶解された電解質による高効率イオン伝導性が得られないことがある。なお、グラフト率とは、グラフト重合前の膜の重量に対する、グラフト重合後の膜の重量とグラフト重合前の膜の重量の重量差の比率を示す。 The weight of the membrane of the present embodiment is preferably in the range of 1.05 to 3.0 times (graft rate 5 to 200%) of the weight of the polymer porous membrane, and 1.15 to 2.0 times (graft). The ratio is more preferably in the range of 15% to 100%. By having such a graft ratio, the water content, liquid retention, water permeability, etc. of the polymer porous membrane can be improved. If the graft ratio is too low, sufficient hydrophilicity cannot be imparted to the diaphragm, and the pressure resistance of the porous membrane when it contains water may not be obtained. When the graft ratio becomes too high, the area swelling ratio of the diaphragm increases, and there is a concern that the physical durability of the diaphragm decreases due to excessive water content. In addition, the pores may be closed due to the expansion of the diaphragm, and high-efficiency ionic conductivity may not be obtained due to the electrolyte dissolved in the liquid fuel. The graft ratio indicates the ratio of the weight difference between the weight of the film after graft polymerization and the weight of the film before graft polymerization with respect to the weight of the film before graft polymerization.
　本実施形態の隔膜に含まれる高分子多孔膜の材質は特に限定されず、発明の効果を阻害しない範囲内で公知の樹脂を用いることができる。例えば、ポリエチレン、ポリプロピレン等のポリオレフィン系樹脂、ポリスチレン系樹脂、ビスフェノールＡ型エポキシポリマー等のエポキシ樹脂、ポリフェニレンサルファイド等のポリサルファイド系樹脂、ポリエーテルケトン等のポリエーテル系樹脂、ポリフッ化ビニリデン、エチレンテトラフルオロエチレン、ポリテトラフフルオロエチレン等のフッ素系樹脂等を挙げることができる。これらの樹脂の中でも、ポリエチレン、ポリプロピレン、ポリスチレン、ビスフェノールＡ型エポキシポリマー、ポリフェニレンサルファイド、ポリエーテルケトン、ポリフッ化ビニリデン、エチレンテトラフルオロエチレン及びポリテトラフフルオロエチレンからなる群より選ばれる少なくとも１種が含まれることが好ましく、ポリエチレン、ポリプロピレン、ポリスチレン、ポリフェニレンサルファイド及びポリエーテルケトンからなる群より選ばれる少なくとも１種を含むことがより好ましく、ポリエチレン、ポリプロピレン及びポリスチレンからなる群より選ばれる少なくとも１種が含まれることがさらに好ましい。耐汚染性、耐腐食性、高分子多孔膜の製造価格等の観点から、ポリエチレンが好ましく、低密度ポリエチレン、高密度ポリエチレン、超高分子量ポリエチレンがより好ましい。高分子多孔膜の強度及び、耐熱性向上の観点から、高密度ポリエチレン、超高分子量ポリエチレンが特に好ましい。なかでも、高強度の高分子多孔膜を得る観点から、重量平均分子量５０万以上、特に１００万以上の超高分子量ポリエチレンが好ましい。これらの樹脂は、単独で又は２種以上を混合して使用してもよい。 The material of the polymer porous membrane contained in the diaphragm of the present embodiment is not particularly limited, and a known resin can be used as long as the effect of the invention is not impaired. For example, polyolefin resins such as polyethylene and polypropylene, polystyrene resins, epoxy resins such as bisphenol A type epoxy polymers, polysulfide resins such as polyphenylene sulfide, polyether resins such as polyether ketone, polyvinylidene fluoride, ethylene tetrafluoro Fluorine resins such as ethylene and polytetrafluoroethylene can be exemplified. Among these resins, at least one selected from the group consisting of polyethylene, polypropylene, polystyrene, bisphenol A type epoxy polymer, polyphenylene sulfide, polyether ketone, polyvinylidene fluoride, ethylene tetrafluoroethylene, and polytetrafluoroethylene is included. It is preferable that at least one selected from the group consisting of polyethylene, polypropylene, polystyrene, polyphenylene sulfide and polyether ketone is included, and at least one selected from the group consisting of polyethylene, polypropylene and polystyrene is included. More preferably. From the viewpoints of contamination resistance, corrosion resistance, production cost of the polymer porous membrane, and the like, polyethylene is preferable, and low density polyethylene, high density polyethylene, and ultrahigh molecular weight polyethylene are more preferable. High-density polyethylene and ultrahigh molecular weight polyethylene are particularly preferable from the viewpoint of improving the strength and heat resistance of the polymer porous membrane. Among these, from the viewpoint of obtaining a high-strength polymer porous membrane, ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more, particularly 1,000,000 or more is preferable. These resins may be used alone or in admixture of two or more.
　これらの樹脂は、架橋されていてもよい。架橋方法は、特に限定されず、樹脂に電子線等を照射する方法、シラン化合物、有機過酸化物等の架橋剤を加える方法等、公知の方法を用いることができる。架橋された樹脂を用いると、高分子基材の強度が向上し、電極の短絡の防止効果が向上することがある。 These resins may be cross-linked. The crosslinking method is not particularly limited, and a known method such as a method of irradiating the resin with an electron beam or the like, a method of adding a crosslinking agent such as a silane compound or an organic peroxide, and the like can be used. When a cross-linked resin is used, the strength of the polymer base material may be improved and the effect of preventing the short circuit of the electrode may be improved.
　高分子多孔膜の平均孔径は、１ｎｍ～１０００ｎｍの範囲にあることが好ましく、２ｎｍ～５００ｎｍの範囲にあることがより好ましく、５ｎｍ～３００ｎｍの範囲にあることがさらに好ましい。平均孔径が大きくなりすぎると、電極間の短絡が生じることがある。また隔膜の耐圧性が低下し、酸化剤の圧力に耐えることが困難になることがある。また、燃料の透過量が多くなることがある。平均孔径が小さくなりすぎると、透水量が低くなることがある。透水量が少なくなりすぎると、カソード触媒における反応に必要な水が不足し、発電効率が低下することがある。後程実施するグラフト重合によって、隔膜全体の平均孔径は変動するので、その変動を想定して多孔膜の平均孔径を調整することが好ましい。 The average pore diameter of the polymer porous membrane is preferably in the range of 1 nm to 1000 nm, more preferably in the range of 2 nm to 500 nm, and still more preferably in the range of 5 nm to 300 nm. If the average pore diameter becomes too large, a short circuit between the electrodes may occur. In addition, the pressure resistance of the diaphragm may be reduced, making it difficult to withstand the pressure of the oxidant. Also, the amount of fuel permeation may increase. If the average pore diameter becomes too small, the water permeability may be lowered. If the water permeation amount is too small, water required for the reaction in the cathode catalyst may be insufficient, and power generation efficiency may be reduced. Since the average pore diameter of the entire diaphragm varies due to graft polymerization performed later, it is preferable to adjust the average pore diameter of the porous membrane in consideration of the variation.
　高分子多孔膜の空孔率は、５～９５％の範囲にあることが好ましく、１０～７０％の範囲にあることがより好ましく、１０％～５０％の範囲にあることがさらに好ましい。空孔率が大きくなりすぎると、燃料の透過が多くなることがある。また、隔膜の耐圧性が低下し、酸化剤の圧力を保てないことがある。空孔率が小さくなりすぎると、透水量が小さくなりすぎることがあり、含水率が低くなることがある。後程実施するグラフト重合によって、隔膜全体の空孔率は変動するので、その変動を想定して多孔膜の空孔率を調整することが好ましい。 The porosity of the polymer porous membrane is preferably in the range of 5 to 95%, more preferably in the range of 10 to 70%, and still more preferably in the range of 10% to 50%. If the porosity is too high, fuel permeation may increase. In addition, the pressure resistance of the diaphragm is reduced, and the pressure of the oxidant may not be maintained. If the porosity is too small, the water permeability may be too small, and the moisture content may be lowered. Since the porosity of the whole diaphragm varies due to graft polymerization performed later, it is preferable to adjust the porosity of the porous membrane in consideration of the variation.
　グラフト鎖の付加によって膜厚が厚くなる傾向を考慮に入れつつ、高分子多孔膜の膜厚は、５μｍ～１００μｍの範囲にあることが好ましく、１０μｍ～５０μｍの範囲にあることがより好ましい。膜厚が薄くなりすぎると、膜強度が低下することがあり、膜の破損やピンホール等の欠陥が生じることがある。また、燃料の透過量及び透水量が多くなることがある。燃料の透過量が多くなると、燃料と酸化剤が直接反応する副反応が生じ、発電効率が悪くなることがあり、またこの副反応によってカソード触媒等の劣化が生じることがある。膜厚が厚くなりすぎると、隔膜内での膜としての抵抗（膜抵抗）が高くなることがある。また、透水量が少なくなりすぎることがある。透水量が少なくなりすぎると、カソード触媒における反応に必要な水が不足し、発電効率が低下することがある。 Taking into consideration the tendency of the film thickness to increase due to the addition of graft chains, the film thickness of the polymer porous film is preferably in the range of 5 μm to 100 μm, and more preferably in the range of 10 μm to 50 μm. If the film thickness becomes too thin, the film strength may decrease, and defects such as film breakage and pinholes may occur. In addition, the fuel permeation amount and water permeation amount may increase. When the permeation amount of the fuel increases, a side reaction in which the fuel and the oxidant directly react with each other occurs, so that the power generation efficiency may deteriorate, and the side reaction may cause deterioration of the cathode catalyst and the like. When the film thickness becomes too thick, the resistance (film resistance) as a film in the diaphragm may increase. In addition, the water permeability may be too small. If the water permeation amount is too small, water required for the reaction in the cathode catalyst may be insufficient, and power generation efficiency may be reduced.
　燃料の透過量が増え、カソード触媒上に燃料が存在すると、燃料と酸化剤とが直接反応する副反応が生じることがあり、電池の発電効率が低下し、副反応によってカソード触媒等が劣化することがある。従って、適切な燃料の透過量を有する隔膜を得るために、高分子多孔膜の膜厚、グラフト率、平均孔径、空孔率、又は透気度（ガーレー値）を選択することが好ましい。 If the amount of permeated fuel increases and the fuel is present on the cathode catalyst, a side reaction in which the fuel and the oxidant directly react may occur, resulting in a decrease in power generation efficiency of the battery, and deterioration of the cathode catalyst and the like due to the side reaction. Sometimes. Therefore, in order to obtain a diaphragm having an appropriate fuel permeation amount, it is preferable to select the film thickness, graft ratio, average pore diameter, porosity, or air permeability (Gurley value) of the polymer porous membrane.
　高分子多孔膜の作製方法は特に限定されず、熱誘起相分離又は非溶媒誘起相分離を利用した乾式成膜法、湿式成膜法等の公知の方法を用いることができる。例えば、無機系発泡剤、有機系発泡剤又は超臨界流体を用いて発泡処理を実施する方法、相溶性の低い高分子基材と相分離化剤とを混合後相分離させ、相分離化剤を抽出用の溶媒（例えば超臨界二酸化炭素）を用いて抽出又は加熱して抽出する処理方法、成膜後に抽出可能な成分を含有する成形体を形成し相分離後、切削して膜を形成し、この膜から抽出可能な成分を除去する処理方法を用いることができる。金型（例えば円筒状）に充填した粉末状の高分子基材を、水蒸気を用いて加熱し、焼結して成形体を形成し、この形成された成形体（例えば円筒状のブロック体）を所定の厚みに切削することによって、多孔膜を得てもよい。 The method for producing the polymer porous membrane is not particularly limited, and a known method such as a dry film formation method or a wet film formation method using thermally induced phase separation or non-solvent induced phase separation can be used. For example, a foaming method using an inorganic foaming agent, an organic foaming agent or a supercritical fluid, a polymer substrate having low compatibility and a phase separation agent are mixed and then phase separated, Extraction or heating using a solvent for extraction (for example, supercritical carbon dioxide), forming a molded body containing components that can be extracted after film formation, phase separation, cutting to form a film In addition, it is possible to use a processing method for removing extractable components from the membrane. A powdery polymer base material filled in a mold (for example, a cylindrical shape) is heated using water vapor and sintered to form a molded body, and the formed body (for example, a cylindrical block body). The porous film may be obtained by cutting the film into a predetermined thickness.
　また、高分子多孔膜の作製方法として、樹脂及び溶媒を含む組成物を溶融混練し、押出し後冷却してシート状成形物とした後、脱溶媒処理を行ってもよい。又は、前記シート状成形物を圧延又は一軸延伸した後、積層し、溶媒を抽出除去することにより積層型の高分子多孔膜を得ることができる。また、積層した後、延伸してもよい。抽出後すぐに貼り合わせて積層することも可能であり、その場合には抽出工程が短時間ですむため生産性を向上できる。高分子多孔膜の作製に用いる溶媒は、高分子多孔膜に含まれる樹脂の溶解が可能な溶媒であれば特に限定されないが、凝固点が－１０℃以下の溶媒が好ましく用いられる。このような溶媒の好ましい具体例として、デカン、デカリン、流動パラフィン等の脂肪族又は脂環式炭化水素、沸点がこれらに対応する鉱油留分等が挙げられる。 Further, as a method for producing the polymer porous membrane, a solvent-containing treatment may be performed after melt-kneading a composition containing a resin and a solvent, cooling after extrusion to form a sheet-like molded product. Alternatively, a laminated polymer porous membrane can be obtained by rolling or uniaxially stretching the sheet-like molded product and then laminating and extracting and removing the solvent. Moreover, after laminating, it may be stretched. It is also possible to bond and laminate immediately after extraction. In that case, the extraction process can be completed in a short time, so that productivity can be improved. The solvent used for preparing the polymer porous membrane is not particularly limited as long as it can dissolve the resin contained in the polymer porous membrane, but a solvent having a freezing point of −10 ° C. or lower is preferably used. Preferable specific examples of such a solvent include aliphatic or alicyclic hydrocarbons such as decane, decalin and liquid paraffin, and mineral oil fractions having boiling points corresponding to these.
　樹脂及び溶媒を含む組成物中の樹脂と溶媒との混合割合は、一概に決定できないが、組成物中の樹脂の濃度が５～３０重量％の範囲にあることが好ましい。樹脂の濃度が高くなりすぎると、混練不足になりポリマー鎖の充分な絡み合いを得にくくなる。樹脂の濃度が低くなりすぎると、高分子多孔膜の充分な強度が得られないことがある。 The mixing ratio of the resin and the solvent in the composition containing the resin and the solvent cannot be generally determined, but the concentration of the resin in the composition is preferably in the range of 5 to 30% by weight. If the concentration of the resin is too high, kneading is insufficient and it becomes difficult to obtain sufficient entanglement of the polymer chains. If the resin concentration is too low, sufficient strength of the polymer porous membrane may not be obtained.
　樹脂及び溶媒を含む組成物中には、必要に応じて、酸化防止剤、紫外線吸収剤、染料、顔料、耐電防止剤、造核等の添加物を、本発明の目的を損なわない範囲でさらに添加することができる。 In the composition containing a resin and a solvent, if necessary, additives such as an antioxidant, an ultraviolet absorber, a dye, a pigment, an antistatic agent, and nucleation are further added as long as the object of the present invention is not impaired. Can be added.
　本実施形態において親水性官能基は、親水性を有する官能基であれば特に限定されないが、例えば水酸基、カルボキシル基、アミノ基、スルホン酸基、リン酸基からなる群より選ばれる少なくとも１つであり、特にカルボキシル基である。 In the present embodiment, the hydrophilic functional group is not particularly limited as long as it is a functional group having hydrophilicity. For example, the hydrophilic functional group is at least one selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, a sulfonic acid group, and a phosphoric acid group. Yes, especially a carboxyl group.
　グラフト鎖は、アニオン交換能を有する官能基を実質的に有していなくてもよい。実質的に有しないとは、隔膜の重量に対するアニオン交換能を有する官能基の量が０．１ｍｍｏｌ／ｇ以下であることを言い、好ましくは０．０５ｍｍｏｌ／ｇ以下であることを言う。アニオン交換能を有する官能基とは、例えば４級アンモニウム塩基、４級ホスホニウム塩基等が挙げられる。このようなグラフト鎖を有することによって、アニオン交換能を有する官能基の劣化の影響が少なく、化学的な耐久性がより良好な隔膜が得られると考えられる。 The graft chain may not substantially have a functional group having anion exchange ability. “Substantially free” means that the amount of the functional group having anion exchange capacity relative to the weight of the diaphragm is 0.1 mmol / g or less, preferably 0.05 mmol / g or less. Examples of functional groups having anion exchange ability include quaternary ammonium bases and quaternary phosphonium bases. By having such a graft chain, it is considered that a membrane having a better chemical durability can be obtained with less influence of deterioration of the functional group having anion exchange ability.
　親水性官能基は、グラフト鎖を形成するモノマー（以下、「グラフトモノマー（Ｍ）」という場合がある）が有していてもよく、グラフト重合後にグラフト鎖に導入されてもよい。すなわち、グラフトモノマー（Ｍ）は、親水性官能基を有していてもよく、親水性官能基を導入しえる部位を有していてもよい。 The hydrophilic functional group may have a monomer that forms a graft chain (hereinafter sometimes referred to as “graft monomer (M)”), and may be introduced into the graft chain after graft polymerization. That is, the graft monomer (M) may have a hydrophilic functional group or may have a site where a hydrophilic functional group can be introduced.
　好ましい一形態において、グラフトモノマー（Ｍ）は炭素－炭素不飽和結合と親水性官能基とを有する。グラフトモノマー（Ｍ）は、特に限定されないが、例えばアクリル酸、メタクリル酸等のカルボン酸モノマー、アクリルアミド、メタクリルアミド、２－ヒドロキシメチルアクリレート、２－ヒドロキシエチルアクリレート、２－ヒドロキシプロピルアクリレート、３－ヒドロキシプロピルアクリレート、４－ヒドロキシブチルアクリレート、２－ヒドロキシメチルメタクリレート、２－ヒドロキシエチルメタクリレート等の（メタ）アクリル酸の誘導体モノマー、酢酸ビニル等の酢酸ビニル系モノマー、アリルアミン、アクリルアミド、メタクリルアミド、Ｎ－ビニルピロリドン、Ｎ－ビニルピリジン等の窒素含有モノマー、スチレンスルホン酸ナトリウム等のスチレン誘導体モノマーが挙げられる。これらの中でもアクリル酸、メタクリル酸、アクリルアミド、メタクリルアミド、Ｎ－ビニルピロリドン、Ｎ－ビニルピリジン、２－ヒドロキシエチルメタクリレート、及びスチレン誘導体モノマーからなる群より選ばれる少なくとも１つが含まれることが好ましく、アクリル酸、メタクリル酸、アクリルアミド、メタクリルアミド、Ｎ－ビニルピロリドン、Ｎ－ビニルピリジン、及び２－ヒドロキシエチルメタクリレートからなる群より選ばれる少なくとも１つが含まれることが好ましい。 In a preferred embodiment, the graft monomer (M) has a carbon-carbon unsaturated bond and a hydrophilic functional group. The graft monomer (M) is not particularly limited, but examples thereof include carboxylic acid monomers such as acrylic acid and methacrylic acid, acrylamide, methacrylamide, 2-hydroxymethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxy (Meth) acrylic acid derivative monomers such as propyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxymethyl methacrylate, 2-hydroxyethyl methacrylate, vinyl acetate monomers such as vinyl acetate, allylamine, acrylamide, methacrylamide, N-vinyl Examples thereof include nitrogen-containing monomers such as pyrrolidone and N-vinylpyridine, and styrene derivative monomers such as sodium styrenesulfonate. Among these, it is preferable to include at least one selected from the group consisting of acrylic acid, methacrylic acid, acrylamide, methacrylamide, N-vinylpyrrolidone, N-vinylpyridine, 2-hydroxyethyl methacrylate, and styrene derivative monomers. Preferably, at least one selected from the group consisting of acid, methacrylic acid, acrylamide, methacrylamide, N-vinyl pyrrolidone, N-vinyl pyridine, and 2-hydroxyethyl methacrylate is included.
　本実施形態のグラフトモノマー（Ｍ）は、アニオン交換能を有する官能基を実質的に有しないことが好ましい。実質的に有しないとは、隔膜の重量に対するアニオン交換能を有する官能基の量が０．１ｍｍｏｌ／ｇ以下であることを言い、好ましくは０．０５ｍｍｏｌ／ｇ以下であることを言う。アニオン交換能を有する官能基とは、例えば４級アンモニウム塩基、４級ホスホニウム塩基等が挙げられる。 It is preferable that the graft monomer (M) of the present embodiment has substantially no functional group having anion exchange ability. “Substantially free” means that the amount of the functional group having anion exchange capacity relative to the weight of the diaphragm is 0.1 mmol / g or less, preferably 0.05 mmol / g or less. Examples of functional groups having anion exchange ability include quaternary ammonium bases and quaternary phosphonium bases.
　グラフトモノマー（Ｍ）は、グラフトモノマー（Ｍ）単独で重合に供してもよく、グラフトモノマー（Ｍ）を溶媒に溶解させた溶液（グラフトモノマー（Ｍ）溶液）として準備してもよい。 The graft monomer (M) may be used for polymerization alone or may be prepared as a solution (graft monomer (M) solution) in which the graft monomer (M) is dissolved in a solvent.
　グラフトモノマー（Ｍ）溶液に含まれる溶媒に特に限定はないが、グラフトモノマー（Ｍ）は溶解するが、高分子多孔膜は溶解しない溶媒を用いると、グラフトモノマー（Ｍ）と高分子多孔膜との分離が容易である。また、副生成物であるグラフトモノマー（Ｍ）のみから形成されたポリマーの溶解が可能である溶媒を用いると、重合液を均一に保つことができる。なお、グラフトモノマー（Ｍ）、グラフトモノマー（Ｍ）のみから形成されたポリマー及び高分子多孔膜の溶媒への溶解性は、グラフトモノマー（Ｍ）、グラフトモノマー（Ｍ）のみから形成されたポリマー及び高分子多孔膜の構造又は極性等によって異なることがあるため、これらの化合物の溶解性に応じて適宜溶媒を選択してもよい。また、２種以上の化合物を混合して溶媒として用いてもよい。 The solvent contained in the graft monomer (M) solution is not particularly limited. If a solvent that dissolves the graft monomer (M) but does not dissolve the polymer porous membrane is used, the graft monomer (M), the polymer porous membrane, Is easily separated. In addition, when a solvent capable of dissolving a polymer formed only from the graft monomer (M) as a by-product is used, the polymerization solution can be kept uniform. The solubility of the graft monomer (M), the polymer formed only from the graft monomer (M) and the polymer porous membrane in the solvent is the polymer formed only from the graft monomer (M), the graft monomer (M), and Since it may vary depending on the structure or polarity of the polymer porous membrane, a solvent may be appropriately selected according to the solubility of these compounds. Two or more compounds may be mixed and used as a solvent.
　このような溶媒としては、具体的には、ベンゼン、トルエン、キシレン等の芳香族炭化水素類、フェノール、クレゾール等のフェノール類等の芳香族化合物を挙げることができる。このような溶媒を用いることによって、グラフト率の高い隔膜を得ることができる。また、芳香族化合物は、副生成物であるグラフトモノマー（Ｍ）のみからなるポリマーを溶解するため、重合液を均一に保つことができる。 Specific examples of such a solvent include aromatic compounds such as aromatic hydrocarbons such as benzene, toluene and xylene, and phenols such as phenol and cresol. By using such a solvent, a diaphragm having a high graft rate can be obtained. In addition, since the aromatic compound dissolves the polymer composed only of the graft monomer (M) as a by-product, the polymerization solution can be kept uniform.
　このグラフトモノマー（Ｍ）溶液中のグラフトモノマー（Ｍ）の濃度は、グラフトモノマー（Ｍ）の重合性や目標とするグラフト率に応じて定めればよいが、例えばグラフトモノマー（Ｍ）溶液全体の重量に対して２０重量％以上のグラフトモノマー（Ｍ）を含ませることが好ましい。グラフトモノマー（Ｍ）の濃度が２０重量％以上の溶液を用いることによって、グラフト反応が充分に進行しない事態を回避しやすくする。 The concentration of the graft monomer (M) in the graft monomer (M) solution may be determined according to the polymerizability of the graft monomer (M) and the target graft ratio. It is preferable to include 20% by weight or more of the graft monomer (M) based on the weight. By using a solution having a concentration of the graft monomer (M) of 20% by weight or more, it is easy to avoid a situation in which the graft reaction does not proceed sufficiently.
　酸素の存在によってグラフト重合反応が阻害されることを防ぐため、グラフトモノマー（Ｍ）又はグラフトモノマー（Ｍ）溶液中の酸素は、凍結脱気や窒素ガス等を用いたバブリング等の公知の方法を用いて除去することが好ましい。 In order to prevent the graft polymerization reaction from being hindered by the presence of oxygen, oxygen in the graft monomer (M) or the graft monomer (M) solution is subjected to a known method such as freeze degassing or bubbling using nitrogen gas. It is preferable to use and remove.
　グラフト鎖は、グラフト重合処理によって高分子多孔膜に導入される。このグラフト鎖は、高分子多孔膜に結合している。グラフト鎖は、均一系で処理できる観点から、放射線グラフト重合処理によって形成されることが好ましい。具体的には、高分子多孔膜に放射線を照射し、放射線照射後の高分子多孔膜とグラフトモノマー（Ｍ）又はグラフトモノマー（Ｍ）溶液とを接触させてグラフト重合反応をさせることによって形成されることが好ましい。 The graft chain is introduced into the polymer porous membrane by graft polymerization. This graft chain is bonded to the polymer porous membrane. The graft chain is preferably formed by a radiation graft polymerization treatment from the viewpoint that it can be treated in a homogeneous system. Specifically, it is formed by irradiating a polymer porous membrane with radiation, bringing the polymer porous membrane after radiation irradiation into contact with a graft monomer (M) or a graft monomer (M) solution to cause a graft polymerization reaction. It is preferable.
　高分子多孔膜に照射される放射線としては、α線、β線、γ線、電子線、紫外線等の電離放射線があり、特にγ線又は電子線が好ましい。照射線量は、好ましくは１ｋＧｙ～４００ｋＧｙの範囲にあり、より好ましくは１０ｋＧｙ～３００ｋＧｙの範囲にある。グラフト率は、放射線の照射量によって制御することができる。照射線量が低すぎるとグラフト率が低くなることがある。照射線量が多くなりすぎると、高分子多孔膜の劣化や過剰な重合反応によって隔膜の機械的強度の低下が生じることがある。 Examples of radiation irradiated to the polymer porous membrane include ionizing radiation such as α rays, β rays, γ rays, electron rays, and ultraviolet rays, and γ rays or electron rays are particularly preferable. The irradiation dose is preferably in the range of 1 kGy to 400 kGy, more preferably in the range of 10 kGy to 300 kGy. The graft rate can be controlled by the radiation dose. If the irradiation dose is too low, the graft rate may be lowered. When the irradiation dose increases too much, the mechanical strength of the diaphragm may be reduced due to deterioration of the polymer porous membrane or excessive polymerization reaction.
　放射線照射後の高分子多孔膜は、低温（例えば－３０℃以下）で保持してもよい。 The polymer porous membrane after irradiation may be held at a low temperature (for example, −30 ° C. or lower).
　酸素の存在によってグラフト重合反応が阻害されることを防ぐため、グラフト重合は、酸素濃度ができる限り低い雰囲気下で行うことが好ましく、アルゴンガスや窒素ガス等の不活性ガス雰囲気下で実施することがより好ましい。 In order to prevent the graft polymerization reaction from being hindered by the presence of oxygen, the graft polymerization is preferably performed in an atmosphere where the oxygen concentration is as low as possible, and is performed in an inert gas atmosphere such as argon gas or nitrogen gas. Is more preferable.
　グラフト重合を実施する温度は、例えば０℃～１００℃であり、特に４０～８０℃である。グラフト重合を実施する反応時間は、例えば２分～１２時間程度である。グラフト率は、これらの反応温度、反応時間によって制御することが可能である。 The temperature at which the graft polymerization is performed is, for example, 0 ° C. to 100 ° C., particularly 40 to 80 ° C. The reaction time for carrying out the graft polymerization is, for example, about 2 minutes to 12 hours. The graft ratio can be controlled by these reaction temperature and reaction time.
　グラフト重合反応の一例として、固液二相系における反応例を述べる。まず、グラフトモノマー（Ｍ）と溶媒とを含むグラフトモノマー（Ｍ）溶液をガラスやステンレス等の容器に入れる。次に、グラフト反応を阻害する溶存酸素を除去するために、グラフトモノマー（Ｍ）溶液中の減圧脱気及び不活性ガス（窒素ガス等）によるバブリングを行う。その後、放射線照射後の高分子多孔膜をグラフトモノマー（Ｍ）溶液に投入してグラフト重合を行う。グラフト重合によって高分子多孔膜を構成するポリマーにグラフト鎖が導入される。次に、得られた膜を反応溶液から取り出して濾別する。さらに、溶媒、未反応のグラフトモノマー（Ｍ）、及びグラフトモノマー（Ｍ）のみからなるポリマーを除去するために、得られた膜を適量の溶剤で３～６回洗浄した後、乾燥させる。溶剤としては、グラフトモノマー（Ｍ）及びグラフトモノマー（Ｍ）のみからなるポリマーが容易に溶解し、グラフト膜が溶解しない溶剤を用いればよい。例えば、溶剤として、水、トルエンやアセトン等を用いることも可能である。 As an example of graft polymerization reaction, a reaction example in a solid-liquid two-phase system will be described. First, a graft monomer (M) solution containing a graft monomer (M) and a solvent is placed in a container such as glass or stainless steel. Next, in order to remove the dissolved oxygen that inhibits the graft reaction, vacuum degassing in the graft monomer (M) solution and bubbling with an inert gas (nitrogen gas or the like) are performed. Thereafter, the polymer porous membrane after irradiation is put into a graft monomer (M) solution to perform graft polymerization. Graft chains are introduced into the polymer constituting the polymer porous membrane by graft polymerization. Next, the obtained membrane is removed from the reaction solution and filtered. Further, in order to remove the polymer composed of only the solvent, the unreacted graft monomer (M), and the graft monomer (M), the obtained film is washed 3 to 6 times with an appropriate amount of solvent and then dried. As the solvent, a solvent that can easily dissolve the graft monomer (M) and the polymer composed only of the graft monomer (M) and does not dissolve the graft film may be used. For example, water, toluene, acetone or the like can be used as the solvent.
　別の実施形態において、グラフトモノマー（Ｍ）は、炭素－炭素不飽和結合と親水性官能基を導入しえる部位とを有する。親水性官能基を導入しえる部位とは、例えばハロゲン化メチル基、ハロゲン化エチル基、ハロゲン化プロピル基、及びハロゲン化ブチル基等のハロゲン化アルキル基、スチレンスルホン酸、ビニルスルホン酸又はアクリルホスホン酸等のアルキルエステル等が挙げられる。グラフトモノマー（Ｍ）は、スチレン、クロロメチルスチレン、ブロモブチルスチレン等のスチレン誘導体が挙げられる。これらのモノマー（Ｍ）は単独で又は２種以上を混合して使用してもよい。本実施形態において、グラフトモノマー（Ｍ）はアニオン交換能を有する官能基を有しないことが好ましい。 In another embodiment, the graft monomer (M) has a carbon-carbon unsaturated bond and a site capable of introducing a hydrophilic functional group. The site capable of introducing a hydrophilic functional group is, for example, a halogenated alkyl group such as a halogenated methyl group, a halogenated ethyl group, a halogenated propyl group, and a halogenated butyl group, styrene sulfonic acid, vinyl sulfonic acid or acrylic phosphone. Examples include alkyl esters such as acids. Examples of the graft monomer (M) include styrene derivatives such as styrene, chloromethylstyrene, and bromobutylstyrene. These monomers (M) may be used alone or in admixture of two or more. In this embodiment, it is preferable that the graft monomer (M) does not have a functional group having anion exchange ability.
　別の実施形態において、本発明の隔膜又はＭＥＡを酸形の液体燃料電池に用いる場合には、隔膜の有するグラフト鎖はカチオン伝導能を有する官能基を実質的に有しないことが好ましい。本実施形態の隔膜の有する親水性官能基は、例えばスルホン酸基である。 In another embodiment, when the diaphragm or MEA of the present invention is used in an acid liquid fuel cell, it is preferable that the graft chain of the diaphragm does not substantially have a functional group having cation conductivity. The hydrophilic functional group which the diaphragm of this embodiment has is a sulfonic acid group, for example.
　別の実施形態において、本発明の特性を有する隔膜は、親水性ゲル、親水性官能基を有する高分子基材からなる無孔膜、又は親水性官能基を有する高分子材料が細孔に充填された多孔膜である。必要に応じて、親水性官能基を有する高分子材料は、架橋構造を有していてもよい。 In another embodiment, the diaphragm having the characteristics of the present invention has a pore filled with a hydrophilic gel, a nonporous membrane made of a polymer base material having a hydrophilic functional group, or a polymer material having a hydrophilic functional group. It is the made porous membrane. If necessary, the polymer material having a hydrophilic functional group may have a crosslinked structure.
　以下、実施例を挙げて本発明をより詳細に説明するが、本発明は、これら実施例に限定されるものではない。 Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.
　実施例及び比較例における物性は以下の方法を用いて測定した。 The physical properties in Examples and Comparative Examples were measured using the following methods.
（Ａ）フィルム厚
　１／１００００直読ダイヤル式膜厚測定器により測定した。 (A) Film thickness It measured with the 1/10000 direct reading dial type film thickness measuring device.
（Ｂ）空孔率
　１／１００００直読ダイヤル式膜厚測定器により測定した厚みを用い、フィルムの単位面積Ｓあたりの重量Ｗ、平均厚みｔ、密度ｄから下式により算出した値を使用した。
　空孔率（％）＝（１－（１０4×Ｗ／Ｓ／ｔ／ｄ））×１００ (B) Porosity Using the thickness measured with a 1/10000 direct reading dial type film thickness measuring device, the value calculated from the weight W per unit area S of the film, the average thickness t, and the density d by the following formula was used.
Porosity (%) = (1− (10 4 × W / S / t / d)) × 100
（Ｃ）含水率
　縦３０ｍｍ横２０ｍｍの矩形に切り出したサンプルを２３℃、相対湿度５０％雰囲気下に２４時間以上放置して、寸法変化が生じなくなった状態のサンプル重量を測定した（含水前の重量）。その後、３０℃の純水中に２時間浸漬し、その後の重量を測定した。含水後の重量は、サンプル表面に付着した余剰な水を濾紙等で拭き取ってから測定した。
　含水率（％）＝（（含水後の重量）－（含水前の重量））×１００／（含水前の重量） (C) Moisture content Samples cut into rectangles of 30 mm in length and 20 mm in width were allowed to stand in an atmosphere at 23 ° C. and 50% relative humidity for 24 hours or longer, and the weight of the sample in a state in which no dimensional change occurred was measured. weight). Then, it was immersed in 30 degreeC pure water for 2 hours, and the subsequent weight was measured. The weight after moisture was measured after wiping off excess water adhering to the sample surface with filter paper or the like.
Moisture content (%) = ((weight after hydration) − (weight before hydration)) × 100 / (weight before hydration)
（Ｄ）面積膨潤率
　縦３０ｍｍ横２０ｍｍの矩形に切り出したサンプルを、２３℃相対湿度５０％の雰囲気下に２４時間以上放置して、寸法変化が生じなくなった状態のサンプルの面積を測定した（含水前の面積）。その後、このサンプルを３０℃の純水中に２時間浸漬した後の面積を測定した（含水後の面積）。面積膨潤率は、以下の式に基づいて計算した比率である。
　面積膨潤率（％）＝（（含水後の面積）－（含水前の面積））×１００／（含水前の面積） (D) Area swelling ratio A sample cut into a rectangle 30 mm long and 20 mm wide was left in an atmosphere of 23 ° C. and 50% relative humidity for 24 hours or more, and the area of the sample in a state in which no dimensional change occurred was measured ( Area before water content). Then, the area after this sample was immersed in 30 degreeC pure water for 2 hours was measured (area after water inclusion). The area swelling rate is a ratio calculated based on the following formula.
Area swelling rate (%) = ((area after water inclusion) − (area before water inclusion)) × 100 / (area before water inclusion)
（Ｅ）重量維持率（耐アルカリ性）
　実施例及び比較例で得られた隔膜について、以下の方法で高温のアルカリ水溶液中における重量維持率（耐アルカリ性）を評価した。まず、隔膜を縦約３ｃｍ横約４ｃｍの矩形に裁断して測定用のサンプルを作製した。このサンプルを、乾燥機中において６０℃雰囲気下に２時間以上乾燥させ、試験片の重量変化が生じなくなった状態の重量（ＫＯＨ処理前の重量）を測定した。このサンプルを、１規定の水酸化カリウム（ＫＯＨ）水溶液（８０℃）に、２１０時間浸漬した。この浸漬処理後、ＫＯＨ水溶液からサンプルを取り出し、純水で複数回洗浄し、大気中にて１晩放置した。次に、乾燥機中において６０℃雰囲気下で乾燥し、乾燥後のサンプルの重量（ＫＯＨ処理後の重量）を測定した。そして、重量維持率を、測定値を用いて以下の式から求め、アルカリ性溶液への耐性の基準とした。
　重量維持率（％）＝（ＫＯＨ処理後の重量）×１００／（ＫＯＨ処理前の重量） (E) Weight retention rate (alkali resistance)
About the diaphragm obtained by the Example and the comparative example, the weight maintenance factor (alkali resistance) in the hot alkaline aqueous solution was evaluated with the following method. First, the diaphragm was cut into a rectangle having a length of about 3 cm and a width of about 4 cm to prepare a sample for measurement. This sample was dried in a dryer at 60 ° C. for 2 hours or longer, and the weight of the test piece in which no change in weight occurred (weight before KOH treatment) was measured. This sample was immersed in a 1N aqueous potassium hydroxide (KOH) solution (80 ° C.) for 210 hours. After this immersion treatment, a sample was taken out from the KOH aqueous solution, washed several times with pure water, and left overnight in the atmosphere. Next, it dried in 60 degreeC atmosphere in dryer, and measured the weight (weight after KOH processing) of the sample after drying. And the weight maintenance factor was calculated | required from the following formula | equation using the measured value, and it was set as the reference | standard of the tolerance to an alkaline solution.
Weight maintenance rate (%) = (weight after KOH treatment) × 100 / (weight before KOH treatment)
（Ｆ）耐圧性試験（主面間耐圧の評価）
　図２～４に示す燃料電池用評価セルを評価用セルとして用いて耐圧性試験を行い、隔膜の主面間耐圧を評価した。
　主面が一辺４ｃｍの正方形である隔膜２を準備した。一辺の長さが２ｃｍの正方形の開口部１１ａ、２１ａを有する、一対のガスケット１１、２１で隔膜２を挟持した。ガスケット１１、２１の外側に、サーペンタイン構造の流路１２ａ、２２ａ付きの一対のセパレータ１２、２２、一対の集電板１３、２３、一対のエンドプレート１４、２４をこの順に配置して挟持した。部材の各接触面から空気、水が漏洩しないように、ボルト等の固定部品（図示せず）を用いて各部材を締結し、評価用セル１００を形成した。
　評価用セル１００は、流路１８、１９、２８、２９を有する。流路１８、１９はそれぞれ水の供給、吐出用の流路であり、流路２８、２９はそれぞれ乾燥空気の供給、吐出用の流路である。各流路１８、１９、２８、２９はエンドプレートに開口を有する。流路１８、１９はエンドプレート１４、集電板１３及びセパレータ１２を貫通し、流路１２ａと連結する。流路２８、２９も同様である。 (F) Pressure resistance test (Evaluation of pressure resistance between main surfaces)
A pressure resistance test was performed using the evaluation cell for fuel cell shown in FIGS. 2 to 4 as an evaluation cell, and the pressure resistance between the main surfaces of the diaphragm was evaluated.
A diaphragm 2 having a main surface of a square having a side of 4 cm was prepared. The diaphragm 2 was sandwiched between a pair of gaskets 11 and 21 having square openings 11a and 21a each having a length of 2 cm. A pair of separators 12 and 22 with serpentine-structured flow channels 12a and 22a, a pair of current collector plates 13 and 23, and a pair of end plates 14 and 24 are arranged and sandwiched in this order on the outside of the gaskets 11 and 21. Each member was fastened using a fixing component (not shown) such as a bolt so that air and water did not leak from each contact surface of the member, and the evaluation cell 100 was formed.
The evaluation cell 100 has flow paths 18, 19, 28, and 29. The channels 18 and 19 are channels for supplying and discharging water, respectively, and the channels 28 and 29 are channels for supplying and discharging dry air, respectively. Each flow path 18, 19, 28, 29 has an opening in the end plate. The flow paths 18 and 19 penetrate the end plate 14, the current collector plate 13, and the separator 12, and are connected to the flow path 12a. The same applies to the flow paths 28 and 29.
　隔膜２の主面が鉛直方向に沿うように評価用セル１００を設置した。この状態の評価用セル１００に水及び乾燥空気の供給を開始した。アノード側の主面（第一主面）へは毎分２ｍｌの水を流路１８に接続した配管３８を介して供給し、カソード側の主面（第二主面）へは毎分５００ｍｌの乾燥空気を流路２８に接続した配管４８を介して供給した。上記のように水を供給し続けることによって、セル１００の第一主面側の内部は供給された水で満たされ、隔膜２の第一主面は常に水と接触した。この際、エンドプレート１４、２４に設けたラバーヒーター１５、２５を用いて評価用セル１００の温度が８０℃になるように評価用セル１００を加熱した。評価用セル１００の温度は、セパレータ２２に設置した熱電対４１を用いて測定した。水及び乾燥空気を上記のように供給し続け、評価用セル１００の温度を８０℃に１時間維持した。 The evaluation cell 100 was installed so that the main surface of the diaphragm 2 was along the vertical direction. Supply of water and dry air to the evaluation cell 100 in this state was started. 2 ml of water per minute is supplied to the main surface on the anode side (first main surface) via a pipe 38 connected to the flow path 18, and 500 ml per minute is supplied to the main surface on the cathode side (second main surface). Dry air was supplied through a pipe 48 connected to the flow path 28. By continuing to supply water as described above, the inside of the first main surface side of the cell 100 was filled with the supplied water, and the first main surface of the diaphragm 2 was always in contact with water. At this time, the evaluation cell 100 was heated using the rubber heaters 15 and 25 provided on the end plates 14 and 24 so that the temperature of the evaluation cell 100 became 80 ° C. The temperature of the evaluation cell 100 was measured using a thermocouple 41 installed in the separator 22. Water and dry air were continuously supplied as described above, and the temperature of the evaluation cell 100 was maintained at 80 ° C. for 1 hour.
　上記状態を１時間維持した後、上記のように水、乾燥空気の供給を続け、かつ評価用セル１００の温度を８０℃に維持しながら、流路２９に接続した配管４９に設けた圧力調整装置（バルブ）４３の開度を調整し、隔膜２の第二主面への乾燥空気の圧力が２０ｋＰａになるように、第二主面への乾燥空気の圧力を昇圧した。乾燥空気の圧力は配管４９に設けた圧力計４２で測定した。その後、水及び乾燥空気を上記のように供給し続け、評価用セル１００の温度を８０℃に維持しながら、第二主面への乾燥空気の圧力を２０ｋＰａに維持できるように圧力調整装置４３の開度を調整した。上記の水及び乾燥空気の供給速度、評価用セル１００の温度、圧力調整装置４３の開度を維持した状態で、第二主面への乾燥空気の圧力を１０分間測定した。２０ｋＰａを１０分間維持できなかった場合には、隔膜の主面間耐圧は０ｋＰａと評価した。２０ｋＰａを１０分間維持できた場合、上記のように水及び乾燥空気を供給し続け、評価用セル１００の温度を８０℃に維持しながら、圧力調整装置４３の開度を調整し、第二主面への乾燥空気の圧力が４０ｋＰａになるように、第二主面への乾燥空気の圧力を昇圧した。その後、水及び乾燥空気を上記のように供給し続け、評価用セル１００の温度を８０℃に維持しながら、第二主面への乾燥空気の圧力を４０ｋＰａに維持できるように圧力調整装置４３の開度を調整した。上記の水及び乾燥空気の供給速度、評価用セル１００の温度、圧力調整装置４３の開度を維持した状態で、第二主面への乾燥空気の圧力を１０分間測定した。４０ｋＰａを１０分間維持できなかった場合には、隔膜の主面間耐圧は２０ｋＰａと評価した。４０ｋＰａを１０分間維持できた場合には、第二主面への乾燥空気の圧力を昇圧し、６０ｋＰａ、８０ｋＰａ、１００ｋＰａの順に同様の測定を行った。第二主面への乾燥空気の圧力を１００ｋＰａに昇圧後、１００ｋＰａを１０分間維持できた場合には、隔膜の主面間耐圧は１００ｋＰａと評価した。ここで、圧力を維持できた場合とは、第二主面への乾燥空気の圧力の変化が、１０分間において１ｋＰａ以下であることをいう。 After maintaining the above state for 1 hour, pressure adjustment provided in the pipe 49 connected to the flow path 29 while continuing to supply water and dry air as described above and maintaining the temperature of the evaluation cell 100 at 80 ° C. The opening degree of the device (valve) 43 was adjusted, and the pressure of the dry air to the second main surface was increased so that the pressure of the dry air to the second main surface of the diaphragm 2 was 20 kPa. The pressure of the dry air was measured with a pressure gauge 42 provided in the pipe 49. Thereafter, the pressure regulator 43 continues to supply water and dry air as described above, and maintains the temperature of the evaluation cell 100 at 80 ° C. so that the pressure of the dry air to the second main surface can be maintained at 20 kPa. The opening degree of was adjusted. With the water and dry air supply rates, the temperature of the evaluation cell 100, and the opening degree of the pressure adjusting device 43 maintained, the pressure of the dry air to the second main surface was measured for 10 minutes. When 20 kPa could not be maintained for 10 minutes, the pressure resistance between the main surfaces of the diaphragm was evaluated as 0 kPa. When 20 kPa can be maintained for 10 minutes, the supply of water and dry air is continued as described above, the opening of the pressure regulator 43 is adjusted while maintaining the temperature of the evaluation cell 100 at 80 ° C., and the second main The pressure of the dry air to the second main surface was increased so that the pressure of the dry air to the surface was 40 kPa. Thereafter, the pressure regulator 43 continues to supply water and dry air as described above so that the pressure of the dry air to the second main surface can be maintained at 40 kPa while maintaining the temperature of the evaluation cell 100 at 80 ° C. The opening degree of was adjusted. With the water and dry air supply rates, the temperature of the evaluation cell 100, and the opening degree of the pressure adjusting device 43 maintained, the pressure of the dry air to the second main surface was measured for 10 minutes. When 40 kPa could not be maintained for 10 minutes, the pressure resistance between the main surfaces of the diaphragm was evaluated as 20 kPa. When 40 kPa could be maintained for 10 minutes, the pressure of dry air to the second main surface was increased, and the same measurement was performed in the order of 60 kPa, 80 kPa, and 100 kPa. When the pressure of dry air on the second main surface was increased to 100 kPa and 100 kPa could be maintained for 10 minutes, the pressure resistance between the main surfaces of the diaphragm was evaluated as 100 kPa. Here, the case where the pressure can be maintained means that the change in the pressure of the dry air to the second main surface is 1 kPa or less in 10 minutes.
（Ｇ）透気度
　日本工業規格（ＪＩＳ）Ｐ８１１７で規定された方法に準拠して、透気度（ガーレー値）を測定した。 (G) Air permeability The air permeability (Gurley value) was measured in accordance with the method defined in Japanese Industrial Standard (JIS) P8117.
（Ｈ）透水速度
　測定は、図２～４に示す燃料電池用評価セルを評価用セルとして用いて以下の手順に従って実施した。
　測定用の隔膜として、一辺４ｃｍの正方形の主面を有する透水速度測定用の隔膜２と、短辺２ｃｍ長辺３ｃｍの矩形の主面を有するＷ３測定用隔膜と、を準備した。 (H) The water permeation rate was measured according to the following procedure using the evaluation cell for fuel cell shown in FIGS. 2 to 4 as the evaluation cell.
As a measurement diaphragm, a water permeability measurement diaphragm 2 having a square main surface with a side of 4 cm and a W3 measurement diaphragm having a rectangular main surface with a short side of 2 cm and a long side of 3 cm were prepared.
　一辺の長さが２ｃｍの正方形の開口部１１ａ、２１ａを有する、一対のガスケット１１、２１で透水速度測定用の隔膜２を挟持した。ガスケット１１、２１の外側に、サーペンタイン構造の流路１２ａ、２２ａ付きの一対のセパレータ１２、２２、一対の集電板１３、２３、一対のエンドプレート１４、２４をこの順に配置して隔膜２挟持した。部材の各接触面から空気、水が漏洩しないように、ボルト等の固定部品（図示せず）を用いて各部材を締結し、評価用セル１００を形成した。
　評価用セル１００は、流路１８、１９、２８、２９を有する。流路１８、１９はそれぞれ水の供給、吐出用の流路であり、流路２８、２９はそれぞれ乾燥空気の供給、吐出用の流路である。各流路１８、１９、２８、２９はエンドプレートに開口を有する。流路１８、１９はエンドプレート１４、集電板１３及びセパレータ１２を貫通し、流路１２ａと連結する。流路２８、２９も同様である。 The diaphragm 2 for measuring the water transmission rate was sandwiched between a pair of gaskets 11 and 21 having square openings 11a and 21a each having a length of 2 cm. A pair of separators 12 and 22 with flow paths 12a and 22a having a serpentine structure, a pair of current collector plates 13 and 23, and a pair of end plates 14 and 24 are arranged in this order on the outside of the gaskets 11 and 21 so as to sandwich the diaphragm 2 did. Each member was fastened using a fixing component (not shown) such as a bolt so that air and water did not leak from each contact surface of the member, and the evaluation cell 100 was formed.
The evaluation cell 100 has flow paths 18, 19, 28, and 29. The channels 18 and 19 are channels for supplying and discharging water, respectively, and the channels 28 and 29 are channels for supplying and discharging dry air, respectively. Each flow path 18, 19, 28, 29 has an opening in the end plate. The flow paths 18 and 19 penetrate the end plate 14, the current collector plate 13, and the separator 12, and are connected to the flow path 12a. The same applies to the flow paths 28 and 29.
　隔膜２の主面が鉛直方向に沿うように評価用セル１００を設置した。この状態の評価用セル１００に水及び乾燥空気の供給を開始した。第一主面へは毎分２ｍｌの水を流路１８に接続した配管３８を介して供給し、第二主面へは毎分５００ｍｌの乾燥空気を流路２８に接続した配管４８を介して供給した。この際、エンドプレート１４、２４に設けたラバーヒーター１５、２５を用いて評価用セル１００の温度が８０℃になるように評価用セル１００を加熱した。評価用セル１００の温度は、セパレータ２２に設置した熱電対４１を用いて測定した。評価用セル１００に水及び乾燥空気を上記のように供給し続け、評価用セル１００の温度を８０℃に１時間維持した。 The evaluation cell 100 was installed so that the main surface of the diaphragm 2 was along the vertical direction. Supply of water and dry air to the evaluation cell 100 in this state was started. 2 ml of water per minute is supplied to the first main surface via a pipe 38 connected to the flow path 18, and 500 ml of dry air per minute is supplied to the second main face via a pipe 48 connected to the flow path 28. Supplied. At this time, the evaluation cell 100 was heated using the rubber heaters 15 and 25 provided on the end plates 14 and 24 so that the temperature of the evaluation cell 100 became 80 ° C. The temperature of the evaluation cell 100 was measured using a thermocouple 41 installed in the separator 22. Water and dry air were continuously supplied to the evaluation cell 100 as described above, and the temperature of the evaluation cell 100 was maintained at 80 ° C. for 1 hour.
　その後、上記のように水及び乾燥空気の供給を続け、かつ評価用セル１００の温度を８０℃に維持しながら、アノード側の流路１９に接続した配管３９から排出された水を３０分間回収した。回収した水の重量をＷ２とした。評価セル１００に３０分間供給した水の重量をＷ１とした。また、Ｗ３測定用隔膜を２３℃相対湿度５５％雰囲気下で２４時間放静置後、測定した重量から計算した隔膜１ｃｍ2あたりの重量をＷ３とした。
　これらの値を用いて、以下の式に従って隔膜の断面方向の透水速度を計算した。
隔膜の断面方向の透水速度［ｍｏｌ/ｈ・ｇ］＝
６０［分］/３０［分］×（Ｗ１－Ｗ２）［ｇ］/１８［ｇ/ｍｏｌ］/４［ｃｍ2］/Ｗ３［ｇ/ｃｍ2］ Thereafter, the water and dry air are continuously supplied as described above, and the water discharged from the pipe 39 connected to the anode-side flow path 19 is collected for 30 minutes while maintaining the temperature of the evaluation cell 100 at 80 ° C. did. The weight of the collected water was W2. The weight of water supplied to the evaluation cell 100 for 30 minutes was defined as W1. Further, after leaving the diaphragm for W3 measurement to stand for 24 hours in an atmosphere of 23 ° C. and 55% relative humidity, the weight per cm 2 of the diaphragm calculated from the measured weight was defined as W3.
Using these values, the water transmission rate in the cross-sectional direction of the diaphragm was calculated according to the following formula.
Permeation rate [mol / h · g] in the cross-sectional direction of the diaphragm =
60 [min] / 30 [min] × (W1-W2) [g] / 18 [g / mol] / 4 [cm 2 ] / W3 [g / cm 2 ]
（Ｉ）電極剥離模擬試験
　実施例又は比較例で得られた隔膜を縦４０ｍｍ横４０ｍｍの正方形状に切り出し、測定用サンプルとした。測定用サンプルを２３℃相対湿度５５％の雰囲気下で１２時間放置して乾燥状態とした後、この測定用サンプルとガス拡散層（ＳＧＬカーボン社製、３５ＢＣ）とを、２５℃、３０ｋｇｆ／ｃｍ2（２．９×１０6Ｐａ）の条件下で３０秒間、圧着させ、ＭＥＡを模した積層体を作製した。作製した積層体を８０℃の水に１２時間浸漬した。その後、８０℃の水中でガス拡散層の剥離の有無を確認した。８０℃の水中で、ガス拡散層と隔膜とが剥離していたサンプルを×、ガス拡散層と隔膜とが剥離せず積層体の形状を維持していたサンプルを〇と評価した。８０℃の水中で積層体の形状を維持していたサンプルは、８０℃の水中から取り出し風乾した後の状態でも積層体の形状を維持していた。 (I) Electrode peeling simulation test The diaphragm obtained in the example or the comparative example was cut into a square shape having a length of 40 mm and a width of 40 mm to obtain a measurement sample. The measurement sample was left to dry for 12 hours in an atmosphere of 23 ° C. and 55% relative humidity, and then the measurement sample and the gas diffusion layer (35BC, manufactured by SGL Carbon Co.) were mixed at 25 ° C. and 30 kgf / cm. 2 was bonded under pressure (2.9 × 10 6 Pa) for 30 seconds to produce a laminate simulating MEA. The produced laminate was immersed in water at 80 ° C. for 12 hours. Then, the presence or absence of peeling of the gas diffusion layer was confirmed in water at 80 ° C. The sample in which the gas diffusion layer and the diaphragm were peeled in water at 80 ° C. was evaluated as x, and the sample in which the gas diffusion layer and the diaphragm were not peeled and the shape of the laminate was maintained was evaluated as “◯”. The sample that maintained the shape of the laminate in water at 80 ° C. maintained the shape of the laminate even after being taken out of the water at 80 ° C. and air-dried.
（Ｊ）メタノール保液率
　予め長辺５０ｍｍ短辺１０ｍｍの矩形に切り出し、２３℃相対湿度５０％の雰囲気下に１２時間以上静置した隔膜を試験片とした。２３℃相対湿度５０％の雰囲気下でメタノールの液面に対して矩形の長辺が垂直になるとともに試験片の底部から５ｍｍの部分がメタノール中に浸漬する状態でメタノールに対して試験片を保持した。メタノール保液率は、この状態を１分間維持した後のメタノールの液面からの吸液高さの長辺に対する比率である。なお、吸液前の試験片は不透明であり、メタノールを吸液した試験片は半透明となる。半透明となった試験片の長さを測定し、吸液高さとした。 (J) Methanol retention ratio A diaphragm, which was previously cut into a rectangle having a long side of 50 mm and a short side of 10 mm, and left in an atmosphere of 23 ° C. and 50% relative humidity for 12 hours or more, was used as a test piece. Hold the test piece against methanol in a state where the long side of the rectangle is perpendicular to the methanol surface and the 5 mm portion from the bottom of the test piece is immersed in methanol in an atmosphere of 23 ° C and 50% relative humidity. did. The methanol retention rate is the ratio of the liquid absorption height from the liquid surface of methanol after maintaining this state for 1 minute to the long side. In addition, the test piece before liquid absorption is opaque, and the test piece which absorbed methanol is translucent. The length of the translucent test piece was measured to obtain the liquid absorption height.
（Ｋ）発電試験
　白金担持カーボンを使用した電極を２０ｍｍの正方形状に切り出し、エチレンジアミンとエタノールとの混合溶液（重量比でエチレンジアミン／エタノール＝３／７）に室温雰囲気下１２時間以上浸漬させた。この電極を風乾後、４０ｍｍの正方形状に切り出した隔膜とガスケットと共に、燃料電池用評価セルを組み立てた。
　上記の燃料電池用評価セルを用いて、電解質を含む液体燃料としてヒドラジン水和物を１０重量％と水酸化カリウムを１ｍｏｌ/Ｌ含む水溶液を、酸化剤として乾燥空気を用いて、４０℃雰囲気下において発電試験を実施した。アノード側へは毎分２ｍｌの液体燃料を供給し、カソード側へは毎分２００ｍｌの乾燥空気を供給した。この試験において、電流掃引の可否、限界電流密度、最大出力密度発現時のセル抵抗（電流遮断法を用いて測定。瞬間的に電流を遮断する際の電圧変化からセルの内部抵抗を測定した。）、及び最大出力密度を比較した。 (K) Power generation test An electrode using platinum-supported carbon was cut into a 20 mm square shape and immersed in a mixed solution of ethylenediamine and ethanol (ethylenediamine / ethanol = 3/7 by weight) for 12 hours or more in a room temperature atmosphere. After this electrode was air-dried, a fuel cell evaluation cell was assembled together with a diaphragm and a gasket cut into a 40 mm square shape.
Using the above fuel cell evaluation cell, an aqueous solution containing 10% by weight of hydrazine hydrate and 1 mol / L of potassium hydroxide as a liquid fuel containing an electrolyte, and dry air as an oxidant, in a 40 ° C. atmosphere. A power generation test was conducted at 2 ml of liquid fuel per minute was supplied to the anode side, and 200 ml of dry air was supplied to the cathode side. In this test, whether or not current sweep is possible, the limit current density, and the cell resistance when the maximum output density was developed (measured using the current interruption method. The internal resistance of the cell was measured from the voltage change when the current was instantaneously interrupted. ) And the maximum power density were compared.
（実施例１）
　実施例１では、高分子基材として、膜厚２０μｍ、空孔率４０％、透気度（ガーレー値）１７３ｓｅｃ／１００ｍｌ・ｉｎｃｈ2の超高分子量ポリエチレン多孔膜を用いた。この超高分子量ポリエチレン多孔膜に、４５ｋＧｙの電子線を照射することで、フリーラジカルを生成させた。電子線照射後の超高分子量ポリエチレン多孔膜を、－７０℃に冷却し、次の工程を実施するまでの間保管した。次に、グラフトモノマー（Ｍ）であるメタクリル酸２５０ｇと、メタノール２５０ｇとを混合してグラフトモノマー（Ｍ）溶液を調製し、温度を２５℃に保ったまま窒素ガスによるバブリングを１時間行うことで、グラフトモノマー（Ｍ）溶液に残存していた酸素を除去した。このグラフトモノマー（Ｍ）溶液に、上記の電子線を照射した超高分子量ポリエチレン多孔膜を投入し、液温を５５℃まで昇温させた。液温を５５℃に維持させながら、６分間重合処理を行い、超高分子量ポリエチレン多孔膜にメタクリル酸をグラフト重合させた。その後、得られたグラフト多孔膜を引き上げて、水洗して余分なモノマーを洗い流した後、表面部分の水分を除き、親水性を有する親水性隔膜を得た。得られたグラフト多孔膜のグラフト率は４０％であった。この隔膜の各物性を測定した。この膜は透気度（ガーレー値）４９１ｓｅｃ／１００ｍｌ・ｉｎｃｈ2であった。この隔膜を用いて発電試験を行った。 (Example 1)
In Example 1, an ultrahigh molecular weight polyethylene porous film having a film thickness of 20 μm, a porosity of 40%, and an air permeability (Gurley value) of 173 sec / 100 ml · inch 2 was used as the polymer substrate. By irradiating this ultrahigh molecular weight polyethylene porous film with an electron beam of 45 kGy, free radicals were generated. The ultrahigh molecular weight polyethylene porous film after electron beam irradiation was cooled to −70 ° C. and stored until the next step was performed. Next, 250 g of methacrylic acid as a graft monomer (M) and 250 g of methanol are mixed to prepare a graft monomer (M) solution, and bubbling with nitrogen gas is performed for 1 hour while maintaining the temperature at 25 ° C. The oxygen remaining in the graft monomer (M) solution was removed. The ultrahigh molecular weight polyethylene porous film irradiated with the electron beam was added to the graft monomer (M) solution, and the liquid temperature was raised to 55 ° C. While maintaining the liquid temperature at 55 ° C., polymerization was performed for 6 minutes, and methacrylic acid was graft-polymerized onto the ultrahigh molecular weight polyethylene porous membrane. Thereafter, the obtained graft porous membrane was pulled up and washed with water to wash away excess monomers, and then water on the surface portion was removed to obtain a hydrophilic diaphragm having hydrophilicity. The resulting graft porous membrane had a graft rate of 40%. Each physical property of this diaphragm was measured. This membrane had an air permeability (Gurley value) of 491 sec / 100 ml · inch 2 . A power generation test was performed using this diaphragm.
（実施例２）
　グラフト重合時間を４分にした以外は、実施例１と同様に実施し、グラフト率３０％の親水性隔膜を得た。この隔膜の各物性を測定した。この膜は透気度（ガーレー値）３６６ｓｅｃ／１００ｍｌ・ｉｎｃｈ2であった。また、この隔膜を用いて発電試験を行った。 (Example 2)
Except for making graft polymerization time into 4 minutes, it implemented similarly to Example 1 and obtained the hydrophilic membrane with a graft ratio of 30%. Each physical property of this diaphragm was measured. This membrane had an air permeability (Gurley value) of 366 sec / 100 ml · inch 2 . In addition, a power generation test was performed using this diaphragm.
（比較例１）
　実施例１で用いた超高分子量ポリエチレン多孔膜を、未処理のまま隔膜として使用した。この隔膜の各物性を測定した。この膜は透気度（ガーレー値）１７３ｓｅｃ／１００ｍｌ・ｉｎｃｈ2であった。また、この隔膜を用いて発電試験を行った。 (Comparative Example 1)
The ultra high molecular weight polyethylene porous membrane used in Example 1 was used as a membrane without treatment. Each physical property of this diaphragm was measured. This membrane had an air permeability (Gurley value) of 173 sec / 100 ml · inch 2 . In addition, a power generation test was performed using this diaphragm.
（比較例２）
　高分子基材として、テトラフルオロエチレンとエチレンの共重合体（ＥＴＦＥ、膜厚５０μｍ）の無孔膜を用いた。このＥＴＦＥ膜に、片面３０ｋＧｙずつ（計６０ｋＧｙ）の電子線を室温真空下において照射することで、フリーラジカルを生成させた。電子線照射後のＥＴＦＥ膜を、－７０℃に冷却し、次の工程を実施するまでの間保管した。次に、４－（クロロメチル）スチレン２８ｇとキシレン１２ｇとを混合してモノマー溶液を調製した。次に、このモノマー溶液を窒素ガスでバブリングすることによって、モノマー溶液内の酸素を除去した。そして、モノマー溶液に、上記の電子線を照射したＥＴＦＥ膜を投入し、液温を７０℃まで昇温させた。液温を７０℃に維持させながら、２時間浸漬することによってグラフト重合を行い、ＥＴＦＥ膜にクロロメチルスチレンをグラフト重合させた。得られた膜のグラフト率は４３．５％であった。次いで、トリメチルアミン水溶液に、上記グラフト膜を室温で２４時間浸漬し、これによって、クロロメチル基の部分の４級化処理を行った。４級化処理後のグラフト膜をエタノールで３０分間洗浄した後、１規定の塩酸を含むエタノール溶液で３０分間洗浄し、さらに純水で洗浄した。このようにして、高分子基材がＥＴＦＥフィルムであり、塩素イオン型の４級アンモニウム塩基を有する膜を得た。この隔膜の各物性を測定した。また、この隔膜を用いて発電試験を行った。 (Comparative Example 2)
As the polymer substrate, a nonporous film of a copolymer of tetrafluoroethylene and ethylene (ETFE, film thickness 50 μm) was used. This ETFE film was irradiated with an electron beam of 30 kGy on each side (total 60 kGy) under vacuum at room temperature to generate free radicals. The ETFE film after electron beam irradiation was cooled to −70 ° C. and stored until the next step was performed. Next, 28 g of 4- (chloromethyl) styrene and 12 g of xylene were mixed to prepare a monomer solution. Next, this monomer solution was bubbled with nitrogen gas to remove oxygen in the monomer solution. And the ETFE film | membrane irradiated with said electron beam was thrown into the monomer solution, and liquid temperature was heated up to 70 degreeC. Graft polymerization was performed by immersing for 2 hours while maintaining the liquid temperature at 70 ° C., and chloromethylstyrene was graft-polymerized on the ETFE membrane. The graft ratio of the obtained film was 43.5%. Subsequently, the graft membrane was immersed in an aqueous trimethylamine solution at room temperature for 24 hours, whereby a quaternization treatment of the chloromethyl group portion was performed. The graft membrane after the quaternization treatment was washed with ethanol for 30 minutes, then washed with an ethanol solution containing 1N hydrochloric acid for 30 minutes, and further washed with pure water. In this way, a polymer base material was an ETFE film, and a film having a chloride ion type quaternary ammonium base was obtained. Each physical property of this diaphragm was measured. In addition, a power generation test was performed using this diaphragm.
　結果を表１にまとめて示す。また、実施例１～２、比較例１～２の隔膜を用いて、電池試験を行った結果を表２にまとめて示す。表１において、ＰＥは超高分子量ポリエチレン、ＣＭＳはクロロメチルスチレン、ＴＭＡはトリメチルアミンを示す。 The results are summarized in Table 1. Table 2 summarizes the results of battery tests using the diaphragms of Examples 1-2 and Comparative Examples 1-2. In Table 1, PE represents ultrahigh molecular weight polyethylene, CMS represents chloromethylstyrene, and TMA represents trimethylamine.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　比較例１で得られた隔膜を用いて耐圧性試験を行ったところ、第二主面への乾燥空気の圧力８０ｋＰａを維持できなかった。ただし、耐圧性試験後の隔膜は、隔膜の外観には変化は見られなかった。 When the pressure resistance test was performed using the diaphragm obtained in Comparative Example 1, the pressure of dry air of 80 kPa on the second main surface could not be maintained. However, the diaphragm after the pressure resistance test showed no change in the appearance of the diaphragm.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　比較例１（親水性官能基を有しないポリエチレン多孔膜）では、電流を取り出せなかったため、他の発電試験を実施できなかった。比較例２（ＥＴＦＥ無孔膜）では、電流は流れたが、セルの内部抵抗が高く限界電流密度が低かった。これに対し実施例１～２（ポリエチレン多孔膜）では、電流を取り出すことができた。すなわち、実施例１～２ではイオン伝導が可能であった。また、限界電流密度は比較例２と比べて高く、最大出力密度発現時のセル抵抗が比較例２よりも低くなった。 In Comparative Example 1 (polyethylene porous membrane having no hydrophilic functional group), since no current could be taken out, other power generation tests could not be performed. In Comparative Example 2 (ETFE nonporous film), current flowed, but the internal resistance of the cell was high and the limiting current density was low. In contrast, in Examples 1 and 2 (polyethylene porous membrane), current could be taken out. That is, in Examples 1 and 2, ion conduction was possible. Moreover, the limiting current density was higher than that of Comparative Example 2, and the cell resistance when the maximum output density was developed was lower than that of Comparative Example 2.

Claims (16)

  1. 　液体燃料電池用隔膜であって、
    　高分子多孔膜と、
    　前記高分子多孔膜に導入されたグラフト鎖と、
    を備え、
    　前記グラフト鎖は親水性官能基を含む、
    　液体燃料電池用隔膜。     A diaphragm for a liquid fuel cell,
    A polymer porous membrane,
    Graft chains introduced into the polymer porous membrane;
    With
    The graft chain includes a hydrophilic functional group;
    Liquid fuel cell membrane.
  2. 　前記親水性官能基が、水酸基、カルボキシル基、スルホン酸基、アミノ基及びリン酸基からなる群より選ばれる少なくとも１つである、
    　請求項１に記載の液体燃料電池用隔膜。     The hydrophilic functional group is at least one selected from the group consisting of a hydroxyl group, a carboxyl group, a sulfonic acid group, an amino group, and a phosphoric acid group;
    The diaphragm for liquid fuel cells according to claim 1.
  3. 　前記液体燃料電池がアルカリ形である、
    　請求項１に記載の液体燃料電池用隔膜。     The liquid fuel cell is alkaline;
    The diaphragm for liquid fuel cells according to claim 1.
  4. 　前記グラフト鎖はアニオン交換能を有する官能基を実質的に有しない、
    　請求項３に記載の液体燃料電池用隔膜。     The graft chain has substantially no functional group having anion exchange ability,
    The diaphragm for liquid fuel cells according to claim 3.
  5. 　前記高分子多孔膜は、ポリエチレン、ポリプロピレン及びポリスチレンからなる群より選ばれる少なくとも１種を含む、
    　請求項１に記載の液体燃料電池用隔膜。     The polymer porous membrane includes at least one selected from the group consisting of polyethylene, polypropylene, and polystyrene.
    The diaphragm for liquid fuel cells according to claim 1.
  6. 　前記グラフト鎖が、アクリル酸、メタクリル酸、アクリルアミド、メタクリルアミド、Ｎ－ビニルピロリドン、Ｎ－ビニルピリジン、２－ヒドロキシエチルメタクリレート及びスチレン誘導体からなる群より選ばれる少なくとも１つのモノマーを重合して得られた、
    　請求項１に記載の液体燃料電池用隔膜。     The graft chain is obtained by polymerizing at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, acrylamide, methacrylamide, N-vinyl pyrrolidone, N-vinyl pyridine, 2-hydroxyethyl methacrylate and styrene derivatives. The
    The diaphragm for liquid fuel cells according to claim 1.
  7. 　第一主面に水を供給しながら、前記第一主面と反対側の第二主面に空気を供給して、前記空気の圧力を上昇させて測定した主面間耐圧が６０ｋＰａ以上である、
    　請求項１に記載の液体燃料電池用隔膜。     While supplying water to the first main surface, air is supplied to the second main surface opposite to the first main surface and the pressure between the main surfaces measured by increasing the pressure of the air is 60 kPa or more. ,
    The diaphragm for liquid fuel cells according to claim 1.
  8. 　断面方向の透水速度が４０ｍｏｌ/ｈ・ｇ以上である、
    　請求項７に記載の液体燃料電池用隔膜。     The water transmission rate in the cross-sectional direction is 40 mol / h · g or more,
    The diaphragm for liquid fuel cells according to claim 7.
  9. 　乾燥時の隔膜の重量に対する、含水時の隔膜の重量と乾燥時の隔膜の重量との重量差の比率が３０重量％以上であり、
    　乾燥時の隔膜の面積に対する、含水時の隔膜の面積と乾燥時の隔膜の面積との面積差の比率が２０％未満である、
    　請求項１に記載の液体燃料電池用隔膜。
    　ここで、乾燥時の隔膜とは、２３℃相対湿度５０％の雰囲気下に２４時間以上放置して寸法変化が生じなくなった状態の隔膜であり、含水時の隔膜とは、前記乾燥時の隔膜を３０℃の水中に２時間浸漬して膨潤させた状態の隔膜である。     The ratio of the weight difference between the weight of the diaphragm when wet and the weight of the diaphragm when dried to the weight of the diaphragm when dried is 30% by weight or more,
    The ratio of the area difference between the area of the diaphragm when wet and the area of the diaphragm when dried to the area of the diaphragm when dried is less than 20%.
    The diaphragm for liquid fuel cells according to claim 1.
    Here, the diaphragm at the time of drying is a diaphragm in a state in which dimensional change does not occur after being left in an atmosphere of 23 ° C. and 50% relative humidity for 24 hours or more. Is a diaphragm in a state where it is swollen by immersion in water at 30 ° C. for 2 hours.
  10. 　メタノール保液率が２０％以上の多孔膜である、
    　請求項１に記載の液体燃料電池用隔膜。
    　ここで、メタノール保液率とは、予め長辺５０ｍｍ短辺１０ｍｍの矩形に切り出し、２３℃相対湿度５０％の雰囲気下に１２時間以上静置した隔膜を試験片とし、２３℃相対湿度５０％の雰囲気下でメタノールの液面に対して前記矩形の前記長辺が垂直になるとともに前記試験片の底部から５ｍｍの部分が前記メタノール中に浸漬する状態で前記メタノールに対して前記試験片を保持し、前記状態を１分間維持した後の前記液面からの吸液高さの前記長辺に対する比率である。     It is a porous membrane having a methanol retention rate of 20% or more.
    The diaphragm for liquid fuel cells according to claim 1.
    Here, the methanol retention rate is a test piece that is a diaphragm that is previously cut into a rectangle having a long side of 50 mm and a short side of 10 mm and left in an atmosphere of 23 ° C. and 50% relative humidity for 12 hours or more. The test piece is held against the methanol in a state where the long side of the rectangle is perpendicular to the liquid level of methanol and a portion 5 mm from the bottom of the test piece is immersed in the methanol under the atmosphere of And the ratio of the liquid absorption height from the liquid level after maintaining the state for 1 minute to the long side.
  11. 　断面方向の透水速度が４０ｍｏｌ/ｈ・ｇ以上であり、
    　かつ第一主面に水を供給しながら、前記第一主面と反対側の第二主面に空気を供給して、前記空気の圧力を上昇させて測定した主面間耐圧が８０ｋＰａ以上である、
    　液体燃料電池用隔膜。     The water transmission rate in the cross-sectional direction is 40 mol / h · g or more,
    And while supplying water to the first main surface, air is supplied to the second main surface opposite to the first main surface and the pressure between the main surfaces measured by increasing the pressure of the air is 80 kPa or more. is there,
    Liquid fuel cell membrane.
  12. 　乾燥時の隔膜の重量に対する、含水時の隔膜の重量と乾燥時の隔膜の重量との重量差の比率が３０重量％以上であり、
    　乾燥時の隔膜の面積に対する、含水時の隔膜の面積と乾燥時の隔膜の面積との面積差の比率が２０％未満である、
    　液体燃料電池用隔膜。
    　ここで、乾燥時の隔膜とは、２３℃相対湿度５０％の雰囲気下に２４時間以上放置して寸法変化が生じなくなった状態の隔膜であり、含水時の隔膜とは、前記乾燥時の隔膜を３０℃の水中に２時間浸漬して膨潤させた状態の隔膜である。     The ratio of the weight difference between the weight of the diaphragm when wet and the weight of the diaphragm when dried to the weight of the diaphragm when dried is 30% by weight or more,
    The ratio of the area difference between the area of the diaphragm when wet and the area of the diaphragm when dried to the area of the diaphragm when dried is less than 20%.
    Liquid fuel cell membrane.
    Here, the diaphragm at the time of drying is a diaphragm in a state in which dimensional change does not occur after being left in an atmosphere of 23 ° C. and 50% relative humidity for 24 hours or more. Is a diaphragm in a state where it is swollen by immersion in water at 30 ° C. for 2 hours.
  13. 　メタノール保液率が２０％以上の多孔膜である、
    　液体燃料電池用隔膜。
    　ここで、メタノール保液率とは、予め長辺５０ｍｍ短辺１０ｍｍの矩形に切り出し、２３℃相対湿度５０％の雰囲気下に１２時間以上静置した隔膜を試験片とし、２３℃相対湿度５０％の雰囲気下でメタノールの液面に対して前記矩形の前記長辺が垂直になるとともに前記試験片の底部から５ｍｍの部分が前記メタノール中に浸漬する状態で前記メタノールに対して前記試験片を保持し、前記状態を１分間維持した後の前記液面からの吸液高さの前記長辺に対する比率である。     It is a porous membrane having a methanol retention rate of 20% or more.
    Liquid fuel cell membrane.
    Here, the methanol retention rate is a test piece that is a diaphragm that is previously cut into a rectangle having a long side of 50 mm and a short side of 10 mm and left in an atmosphere of 23 ° C. and 50% relative humidity for 12 hours or more. The test piece is held against the methanol in a state where the long side of the rectangle is perpendicular to the liquid level of methanol and a portion 5 mm from the bottom of the test piece is immersed in the methanol under the atmosphere of And the ratio of the liquid absorption height from the liquid level after maintaining the state for 1 minute to the long side.
  14. 　前記液体燃料電池がアルカリ形である、
    　請求項１１～１３のいずれか１項に記載の液体燃料電池用隔膜。     The liquid fuel cell is alkaline;
    The diaphragm for a liquid fuel cell according to any one of claims 11 to 13.
  15. 　第一主面に水を供給しながら、前記第一主面と反対側の第二主面に空気を供給して、前記空気の圧力を上昇させて測定した主面間耐圧が６０ｋＰａ以上である、
    　請求項１３に記載の液体燃料電池用隔膜。     While supplying water to the first main surface, air is supplied to the second main surface opposite to the first main surface and the pressure between the main surfaces measured by increasing the pressure of the air is 60 kPa or more. ,
    The diaphragm for liquid fuel cells according to claim 13.
  16. 　請求項１、１１～１３のいずれか１項に記載の液体燃料電池用隔膜を備えた膜－電極接合体。 A membrane-electrode assembly comprising the diaphragm for a liquid fuel cell according to any one of claims 1, 11 to 13.
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