CN117747866A - Proton exchange membrane and preparation method thereof - Google Patents
Proton exchange membrane and preparation method thereof Download PDFInfo
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- CN117747866A CN117747866A CN202410007847.6A CN202410007847A CN117747866A CN 117747866 A CN117747866 A CN 117747866A CN 202410007847 A CN202410007847 A CN 202410007847A CN 117747866 A CN117747866 A CN 117747866A
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Classifications
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- 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
Abstract
The invention relates to a proton exchange membrane and a preparation method thereof, the proton exchange membrane comprises a first exchange layer, an intermediate layer and a second exchange layer, the intermediate layer comprises a support layer, an ion exchange material filled in the support layer and water storage holes, the equivalent weight Ew of the ion exchange material is not higher than 1600, and the thickness H of the proton exchange membrane in a dry state Dry Not higher than 17 μm, the density coefficient I of the proton exchange membrane is 0.15-0.65, and the mass m of the supporting layer per unit area is in a dry state P 2-10g; thickness h of support layer in dry state p 2-8 μm. The existence of the water storage holes reduces the difficulty of forming a proton transmission channel by the proton membrane by reducing the water permeation resistance, reduces the flooding possibility under the high-humidity condition and the disconnection possibility of the proton transmission channel under the high-temperature low-humidity condition, and ensures high proton conductivity; in addition, the existence of water storage holes is improvedThe swelling deformation space of the ion exchange material is provided, so that the dimensional stability of the proton membrane is improved.
Description
Technical Field
The invention relates to the field of fuel cells, in particular to a proton exchange membrane and a preparation method thereof.
Background
With the worsening of environmental problems and exhaustion of fossil fuels, sustainable energy technologies are beginning to be explored. The fuel cell can directly convert chemical energy into electric energy, and has the advantages of high energy conversion efficiency, green environmental protection and the like. Fuel cells are largely classified into Proton Exchange Membrane Fuel Cells (PEMFCs), alkaline fuel cells, phosphoric acid fuel cells, and solid oxide fuel cells.
Proton Exchange Membrane Fuel Cells (PEMFCs) have the advantages of high efficiency, low-temperature operation, convenient operation, safety, reliability and the like, and are widely applied to the fields of electric automobiles, military and the like, wherein the proton exchange membrane is taken as a core component of the proton exchange membrane fuel cells and is known as a chip of the proton exchange membrane fuel cells. Proton exchange membranes have been mass produced from the global market of applications.
For example, japanese patent application publication No. JP2006260811a (the product of the company of asahi corporation) discloses an electrolyte membrane for a solid polymer electrolyte fuel cell, which is made of a polymer compound having a sulfonic acid group (perfluorocarbon polymer having a sulfonic acid group). Perfluorocarbon polymers having sulfonic acid groups (perfluorosulfonic acid resins) are good proton conductors, and proton exchange membranes (electrolyte membranes) are produced from perfluorosulfonic acid resins, meaning that the proton exchange membranes have good proton conductivity. However, with the development of proton exchange membranes, the proton exchange membranes gradually tend to be thin (from tens of micrometers to tens of micrometers), and the lower the proton exchange membrane thickness, the shorter the proton transmission path of the proton exchange membrane, that is, the lower the internal resistance of the proton exchange membrane. However, a low thickness of the proton exchange membrane also means that the mechanical strength and durability thereof are relatively poor, and mechanical damage occurs when the proton exchange membrane is operated for a long period of time.
In order to make the proton exchange membrane with low thickness still have higher durability, a series of reinforced composite membranes have been studied, and at present, the proton exchange membrane has been gradually changed from pure perfluorosulfonic acid resin material to composite material using expanded polytetrafluoroethylene (e-PTFE) membrane as reinforcing material.
For example, chinese patent publication No. CN1134288C (w·l·gol and homogin limited) discloses a composite membrane comprising an expanded polytetrafluoroethylene membrane having a porous microstructure of polymer filaments; and an ion exchange material impregnated throughout the membrane, the ion exchange material including, but not limited to, perfluorosulfonic acid resin, the impregnated expanded polytetrafluoroethylene membrane having a Gurley number greater than 10000 seconds, wherein the ion exchange material substantially fills the membrane such that the membrane interior volume is substantially enclosed.
For another example, a solid polymer electrolyte membrane is disclosed in chinese patent application publication No. CN101273487a (w·l·gol, co-owned limited), which comprises a composite membrane consisting essentially of: (a) At least one expanded PTFE membrane having a porous microstructure of polymeric fibrils, and (b) at least one ion exchange material filled in all of the porous microstructures of the expanded PTFE membrane such that the interior volume of the expanded PTFE membrane is substantially closed.
The proton exchange membranes in the two patent documents are composite membranes, wherein the PTFE membrane plays a role in strengthening, so that the thin-film proton exchange membrane is ensured to have higher mechanical strength, and the probability of mechanical damage of the thin-film proton exchange membrane is reduced. Further, a thin-film proton exchange membrane also tends to mean that it has a smaller internal resistance, and thus fuel cells employing a thin-film proton exchange membrane tend to have better electrical performance.
However, the thin proton exchange membrane has certain disadvantages, for example, the proton exchange membrane has high proton conductivity and high dimensional stability. This is because the PTFE material does not have proton conductivity, and therefore, after the proton exchange membrane is introduced into the PTFE membrane, the PTFE membrane must be filled with a perfluorosulfonic acid resin (ion exchange material) to secure the proton conductivity of the proton exchange membrane. It is believed that an increased content of perfluorosulfonic acid resin is advantageous in increasing proton conductivity, i.e., the more perfluorosulfonic acid resin (the more sulfonic acid groups) is filled in the PTFE membrane, the higher the proton conductivity of the proton exchange membrane. In the existing proton exchange membrane preparation process, a method similar to the method consistent with the patent document is basically adopted, so that the ion exchange material is fully filled with the PTFE layer as much as possible, and the perfluorinated sulfonic acid resin with stronger proton conductivity is adopted, so that the proton exchange membrane is ensured to have higher mechanical strength and higher proton conductivity.
However, after the PTFE layer is completely filled with the perfluorosulfonic acid resin (ion exchange material), the high proton conductivity of the proton exchange membrane is ensured, but the dimensional stability of the proton exchange membrane is also insufficient. This is because the proton exchange membrane is a proton-hydrated membrane (H 3 O + ) I.e. proton exchange membranes, which are necessarily required to absorb a certain amount of moisture (wet) in operation, the swelling of the ion exchange material (perfluorosulfonic acid resin) by water absorption is a necessary phenomenon. The ion exchange material with high filling degree also means that the deformation amount of the proton exchange membrane is relatively large when the proton exchange membrane absorbs water and swells, and the deformation amount of the proton exchange membrane which continuously and reciprocally deforms is relatively large and is more easily damaged in the processes of absorbing water, swelling, dehydrating and drying.
In order to solve the problem of poor dimensional stability of the proton exchange membrane, the following method is selected by a researcher: the thickness of the PTFE film is appropriately increased, and a perfluorosulfonic acid resin having a relatively better quality (a relatively higher sulfonic acid group content) is used. However, the relatively better quality (relatively higher sulfonic acid group content) of the perfluorosulfonic acid resin also tends to mean that the proton exchange membrane has better water swelling properties, and the above-described manner has limited effect on improving the problem of relatively weaker dimensional stability of the proton exchange membrane.
In view of the foregoing, it would be desirable to provide a proton exchange membrane having both high proton conductivity and high dimensional stability.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention aims to provide a proton exchange membrane and a preparation method thereof, wherein the proton exchange membrane has high proton conductivity and high dimensional stability and has longer service life.
In order to achieve the above purpose, the present invention provides the following technical solutions:
in a first aspect, the present application provides a proton exchange membrane, which adopts the following technical scheme:
a proton exchange membrane comprising a first exchange layer, an intermediate layer and a second exchange layer, wherein the first exchange layer is provided with a compact first outer surface, the second exchange layer is provided with a compact second outer surface, the first exchange layer and the second exchange layer are both prepared from ion exchange materials, and the intermediate layer comprises a support layer, ion exchange materials partially filled in the support layer and water storage holes positioned in the support layer; thickness H of the proton exchange membrane in a dry state Dry Not higher than 17 μm;
the compactness coefficient I of the proton exchange membrane is 0.15-0.65, and is obtained through the following formula: i=m n /(m n +m P ) X 100%, where m n Is in a dry state and is filled in a unit area (1 m 2 ) The mass of the ion exchange material in the support layer of the proton exchange membrane is as follows: g; m is m P In a dry state, a unit area (1 m 2 ) The mass of the support layer of the proton exchange membrane is as follows: g; m is m n Calculated by the following formula: m is m n ＝M 0 -(m P +ρ n V n ) Wherein M is 0 In a dry state, a unit area (1 m 2 ) The mass of the proton exchange membrane is as follows: g; ρ n In dry state, the ion exchange material has a density in g/m 3 ；V n In dry state, the sum of the volumes of the first exchange layer and the second exchange layer in the proton exchange membrane is expressed as m 3 ；
Mass m of support layer of proton exchange membrane in dry state P 2-10g; thickness h of the support layer in the dry state p 2-9 μm, the unit area is 1m 2 。
By adopting the technical scheme, in the membrane body structure of the proton exchange membrane provided by the invention, along the membrane thickness direction, the membrane can be clearly seen to comprise three layers of structures, namely a first exchange layer, a middle layer and a second exchange layer. In Proton Exchange Membrane Fuel Cells (PEMFC), on the one hand, the proton exchange membrane is required to be a permselective membrane, only of the mass Son (H) + ) The transfer provides a channel (ensuring good proton conductivity), on the other hand, the proton exchange membrane needs to act as a membrane to block the fuel of the anode from the oxidant of the cathode (ensuring lower gas permeability). Thus, the first exchange layer and the second exchange layer of the proton exchange membrane are both made of ion exchange materials, and both surfaces (the first outer surface and the second outer surface) of the membrane are dense. In the application, the supporting layer is introduced between the first exchange layer and the second exchange layer, so that the proton exchange membrane with thin film thickness (the thickness is not higher than 17 mu m) is ensured to have higher mechanical strength, and the probability of mechanical damage in the use process is reduced. Since the support layer cannot conduct protons, the support layer must be filled with an ion exchange material (a passage for conducting protons in the film thickness direction is formed by the ion exchange material being continuously distributed). It is believed that an increased level of ion exchange material is beneficial in increasing proton conductivity, i.e., the more ion exchange material is filled in the support layer, the higher the proton conductivity of the proton exchange membrane (which is also why gol is fully filled with the pore structure in the PTFE layer using perfluorinated sulfonic acid resins as described above).
However, the inventors of the present application have unexpectedly found that when the ion exchange material in the support layer does not completely fill the pore structure in the support layer (the packing fraction I is 0.15 to 0.65), a plurality of pore structures (water storage pores) exist in the support layer, and that in the dry state of the proton exchange membrane, the pore structure per unit area (1 m 2 ) Mass m of support layer of proton exchange membrane of (2) P Thickness h of 2-10g p It is unexpected that proton exchange membranes have better proton conductivity and also higher dimensional stability at 2-9 μm.
This is probably because the proton exchange membrane is a proton-hydrated membrane (H 3 O + ) The proton conductivity of the proton exchange membrane is closely related to the water content of the proton exchange membrane. Therefore, when the proton exchange membrane fuel cell actually works, the fuel gas and the oxidant gas of the cathode and the anode are required to be humidified, so that the full wetting of the proton exchange membrane is ensured, and the proton exchange membrane is further ensuredHas high proton conductivity and ensures good output power of the proton exchange membrane fuel cell.
However, if the proton exchange membrane in the fuel cell adopts a completely filled proton exchange membrane (the pore structure of the proton exchange membrane supporting layer is completely filled with the ion exchange material), on one hand, the ion exchange material in the proton exchange membrane is relatively more, the proton exchange membrane needs more moisture to be fully wetted, and on the other hand, since the proton exchange membrane is completely compact, the water mass transfer resistance when water permeates the proton exchange membrane is relatively larger, and thus more water mass transfer driving force is needed, when the proton exchange membrane fuel cell actually works, the fuel gas and the oxidant gas of the cathode and the anode need to have higher humidity to ensure that the proton exchange membrane can be well wetted. However, the larger humidification of the fuel gas also easily causes that part of water is accumulated on the surface of the proton exchange membrane, so that the mass transfer resistance of protons is increased, the flooding phenomenon of the fuel cell is further caused, the internal resistance of the fuel cell is increased, and the output power is reduced.
If the proton exchange membrane in the fuel cell adopts the incompletely filled proton membrane provided by the application, the proton exchange membrane supporting layer has proper content of ion exchange material (the compaction coefficient I is 0.15-0.65) and a plurality of water storage holes with water storage function. First, the relatively less ion exchange material in the support layer of the proton exchange membrane provided herein, as compared to a fully filled proton exchange membrane, suggests that the proton exchange membrane requires relatively less moisture to be fully wetted. Furthermore, as the support layer is internally provided with the water storage holes, the existence of the water storage holes can reduce the permeation resistance of water penetrating the proton exchange membrane to a certain extent, and the water storage holes have a certain water storage function, so that the water in the water storage holes can further ensure the good wetting of the inside of the proton exchange membrane. Under the combined action of proper filling quantity and proper water storage holes, the cathode and anode gases can be fully wetted by only needing lower-amplitude humidification in the actual operation of the fuel cell. Because the humidification degree of the gas at the cathode and anode is relatively low, the fuel cell is not easy to be flooded, and the output power of the fuel cell is further ensured. Therefore, in order to ensure that the support layer has a suitable number and volume of water storage holes, the filling amount of the ion exchange material in the support layer cannot be too high, i.e. the compaction factor of the support layer cannot be too high (I not higher than 0.65). Of course, in order to ensure the most basic proton conductivity of the proton exchange membrane, the packing fraction of the ion exchange material in the support layer should not be too low (I is not less than 0.15).
It should be noted that the specific compaction factor I is specific to the support layer having a specific morphology, and the support layer provided in the present application is a specific compaction factor per unit (1 m 2 ) The support layer has a suitable mass of 2-10g and a suitable thickness of 2-9 μm, a suitable mass m P And a suitable thickness h p Indicating that the support layer is internally provided with a suitable volumetric pore structure. The support layer is internally provided with a pore structure with a proper volume, and the support layer is combined with an ion exchange material with a proper filling amount to ensure that the proton exchange membrane is internally provided with water storage pores with a proper volume and the most basic proton conductivity of the proton exchange membrane. It will be appreciated that due to the mass m of the support layer P It is known that the value per unit area (1 m 2 ) In proton membranes, the theoretical volume of the support layer (the size of the three-dimensional space occupied by the support layer if the support layer is a fully dense body that does not contain any pore structure). At the same time, due to the actual thickness h of the supporting layer p It is known that the value of the total amount of the catalyst per unit area (1 m 2 ) The difference between the actual volume and the theoretical volume is the volume of the pore structure in the support layer. Thus, a suitable mass m P And a suitable thickness h p Indicating that the support layer is internally provided with a suitable volumetric pore structure.
If per unit area (1 m 2 ) Mass m of support layer of (2) P Too small a thickness h p Too high (m) P < 2g and h p > 8 μm), which means that the whole support layer is too loose, the number of pore structures in the support layer is too large, the volume is too large, even if the interior is filled with a certain amount of ion exchange material, the interior of the support layer can beThe water storage holes with larger quantity and volume can still exist, the water storage holes can naturally reduce the water permeation resistance of the proton exchange membrane and ensure the water storage capacity inside the proton exchange membrane, however, the existence of the water storage holes also often means that a plurality of open circuits exist in the proton exchange membrane, and once the quantity of the water storage holes is too large and the volume is too large, the existence of the water storage holes also means that the open circuits in the proton exchange membrane are too large, and the proton conductivity of the proton exchange membrane is still lower. If per unit area (1 m 2 ) Mass m of support layer of (2) P Too large a thickness h p Too low (m) P > 10g and h p < 2 μm), which indicates that the support layer is too dense overall, and that there is not enough space within the support layer for the ion exchange material to fill, and that proton conductivity of the proton exchange membrane is not guaranteed. Even if the support layer is filled with a sufficient amount of ion exchange material, the proton exchange membrane may already be in a state of being nearly completely filled, i.e. there are no sufficient number and volume of water storage holes in the support layer of the proton exchange membrane, the water permeation resistance of the proton exchange membrane is still high, and the proton conductivity is still low.
In addition, under some special circumstances, for example, in a high-temperature low-humidity environment, the incompletely filled proton exchange membrane also has higher proton conductivity than the completely filled proton exchange membrane. This is probably because, under the environment of high temperature low humidity, proton exchange membrane hardly by fully wetting, however, because the supporting layer inside of proton exchange membrane that this application provided has a certain quantity to deposit the water hole, deposit the water hole and given the proton exchange membrane certain water and hold the water function, reduce water penetration resistance, improve water distribution's homogeneity for the proton exchange membrane everywhere has relatively good wetting, also ensures the water in the proton exchange membrane is difficult for volatilizing simultaneously, thereby guarantee that the proton exchange membrane of this application also can have higher proton conductivity under the operating mode of high temperature low humidity, and then guarantee battery output. For a completely filled proton membrane, on one hand, the support layer contains more ion exchange materials, so that the proton exchange membrane needs more water to be fully wetted, and the proton membrane with high water requirement cannot obtain sufficient water because of the drier air environment, so that the proton exchange membrane is difficult to be fully wetted; on the other hand, because the support layer of the proton exchange membrane lacks a hole structure with water retention and water storage functions, under the environment that the air environment is dry and the air temperature is relatively high, the permeation resistance of water is large and the water is more easily volatilized, so that the proton exchange membrane is difficult to sufficiently wet, the actual proton conductivity of the proton exchange membrane is not high, and the output power of the battery is lower.
If the compactness coefficient I is too large (more than 0.65), the ion exchange materials in the supporting layer are too much and the hole structures are too small, the water storage and water retention capacity of the whole proton exchange membrane is relatively low, and the proton exchange membrane is difficult to sufficiently wet in a high-temperature low-humidity environment; if the compaction factor I is too small (less than 0.15), which means that the ion exchange material in the support layer is too small, the most basic proton conductivity of the proton exchange membrane cannot be ensured. In the application, the most basic proton conductivity of the proton exchange membrane is ensured by controlling the content (I > 0.15) of the ion exchange material in the supporting layer. Meanwhile, the thickness of the proton exchange membrane is not more than 17 mu m, the thinned proton exchange membrane has lower internal resistance, and under the combined action of proper thickness and filling quantity, the proton conduction capacity of the proton exchange membrane is further ensured, so that the output power of a fuel cell is further ensured.
Furthermore, the inventors of the present application have unexpectedly found that the service life of the incompletely filled proton exchange membrane provided herein is significantly longer than that of a completely filled proton exchange membrane. This is possible because, first, per unit area (1 m 2 ) The proton membrane of the (2) has a supporting layer with proper quality, thickness and compactness, and proper mechanical properties are endowed to the proton exchange membrane. Secondly, the proton exchange membrane must absorb a certain amount of moisture (wetting) in operation, and the water absorption swelling of the ion exchange material is a certain phenomenon, while the incompletely filled proton exchange membrane provided by the application provides a certain swelling space for the ion exchange material due to a certain water storage hole in the support layer, namely, a part of the ion exchange material can be used forSwelling in the supporting layer ensures that the deformation quantity generated when the proton exchange membrane absorbs water and swells is relatively small. Thus, the thickness of the proton exchange membrane does not exceed 17 mu m and the thickness h of the supporting layer p The filling coefficient of the supporting layer is not higher than 0.65 and is 2-9 mu m, and the supporting layer is ensured to have proper water storage effect and simultaneously is further ensured to have enough deformation space. Under the synergistic effect of the three, the deformation of the proton exchange membrane is further controlled in a smaller range, so that the deformation of the proton exchange membrane is not close to a damage threshold, namely the proton exchange membrane has higher dimensional stability, and the proton exchange membrane has better service life. The damage threshold is the maximum deformation that can be tolerated before damage to the proton exchange membrane occurs.
The compaction factor I in the application is calculated by the following formula: i=m n /(m n +m P ) X 100%, where m n Is in a dry state (1 m 2 ) The proton membrane of which is the mass of the ion exchange material partially filled in the pore structure of the support layer, and the unit is: g; m is m P Is in a dry state (1 m 2 ) The mass of the support layer of the proton membrane is as follows: g; in the present application, m P 2-10g, m P Obtained by selecting a proton exchange membrane of a certain area, e.g. 2625mm 2 (25 mm by 75 mm) or 3750mm 2 (50 mm multiplied by 75 mm), putting the proton exchange membrane into a hydrothermal reaction kettle according to the actual situation, soaking the proton exchange membrane in a methanol water solution (the ratio of methanol to water is 4:1) at 180 ℃ for 24 hours, then considering that the methanol water solution can basically completely dissolve the ion exchange material of the proton exchange membrane (the proton exchange membrane at the moment basically only remains a supporting layer), taking out and drying the supporting layer, weighing the mass of the supporting layer, and obtaining the ion exchange membrane with the weight of 1m per unit area (1 m by conversion) 2 ) In proton membrane, the mass of the support layer. m is m n Calculated by the following formula: m is m n ＝M 0 -(m P +ρ n V n ) Wherein M is 0 Is in a dry state (1 m 2 ) A kind of electronic deviceThe proton membrane is dried for 2 hours under the conditions of constant temperature and humidity (30 ℃ and 25 percent RH), and the unit is: g; ρ n In dry state, the ion exchange material has a density in g/m 3 ；V n In dry state, the sum of the volumes of the first exchange layer and the second exchange layer in the proton exchange membrane is expressed as m 3 Wherein the first exchange layer and the second exchange layer are "dense", which means in particular that the area ratio of the pores inside the first exchange layer and the second exchange layer is not more than 5%, i.e. that no pore structure or a very small number of pore structures can be observed, or that the membrane is substantially impermeable to air, and that the Gurley number is more than 10000 seconds.
The term "dense" in the present invention means that the first and second outer surfaces have a void area ratio of not more than 5% when photographed by scanning electron microscopy at 50000 times, i.e., there are two cases where no void structure can be observed or very few void structures can be observed, or the film is substantially impermeable to air, and the Gurley number is more than 10000 seconds. It will be appreciated that by observing the first and second outer surfaces of the proton exchange membrane, it is sometimes found that there are a number of disordered cracks in the first and second outer surfaces, which may be caused by bombardment of the first and second outer surfaces by the electron beam when the scanning electron microscope performs nano-scale resolution image analysis on the sample, and therefore the disordered cracks on the first and second outer surfaces should not be considered as pore structures, and the first and second outer surfaces of the membrane are still dense.
The term "ion exchange material" as used herein includes, but is not limited to, the following compounds and combinations of the following compounds: perfluorosulfonic acid polymers, perfluorocarboxylic acid polymers, perfluorophosphonic acid polymers, styrenic ion exchange polymers, fluorostyrene ion exchange polymers, polyaryletherketone ion exchange polymers, polysulfone ion exchange polymers, bis (fluoroalkyl sulfonyl) imides, (fluoroalkyl sulfonyl) (fluorosulfonyl) imides, polyvinyl alcohol, polyethylene oxide, divinylbenzene, metal salts with or without polymers, and mixtures thereof. The ion exchange material is preferably a perfluorinated sulfonic acid resin.
The material of the support layer comprises two types of substances: fluorine-containing materials or non-fluorine-containing materials, which may include, but are not limited to, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or Polytrifluoroethylene (PCTFE), etc.; the non-fluorine containing material may include, but is not limited to, polyimide (PI), polybenzimidazole (PBI), polyethersulfone (PES), etc., preferably Polytetrafluoroethylene (PTFE).
When the thickness of the proton exchange membrane and the thickness of the supporting layer are measured, the proton exchange membrane is dried for 2 hours under constant temperature and humidity (30 ℃ and 25%RH), and then the section of the membrane is characterized by a scanning electron microscope to obtain a corresponding SEM (scanning electron microscope) image, and the thickness of the proton membrane and the thickness of the supporting layer are measured by corresponding computer software or manually; of course, the person skilled in the art can also obtain the above parameters by other measuring means, which are only used as reference.
Optionally, the swelling value D of the proton exchange membrane is 0.2-1.5, and the swelling value D is calculated by the following formula: d= (H) Moistening device -H Dry )/H Dry Wherein H is Moistening device Is the thickness of the proton exchange membrane in a saturated wetting state after water absorption swelling, and the unit is mu m.
By adopting the technical scheme, the swelling value D of the proton exchange membrane reflects the thickness change of the proton exchange membrane in a dry film state and in a wet state, and the volume change of the whole proton exchange membrane is reflected to a certain extent. In the application, the proton exchange membrane has a proper swelling value D (0.2-1.5), which further demonstrates that the proton exchange membrane has smaller deformation in the swelling and dehydration processes. Under smaller deformation quantity, mechanical damage is not easy to occur to the proton exchange membrane (or the probability of mechanical damage is very small), so that the service life of the proton exchange membrane is obviously prolonged. In addition, the proper swelling value also further indicates that the support layer adopted by the application has proper thickness and compactness, so that the deformation of the proton membrane is relatively smaller, and meanwhile, the deformation of the proton exchange membrane is further reduced due to the introduction of the water storage holes. Of course, in order to ensure the proton conductivity of the proton exchange membrane, it is still necessary to ensure that the support layer has a suitable content of ion exchange material, and to ensure that the number and volume of water holes in the support layer are not excessive (circuit breaking is not excessive), so that the proton exchange membrane needs to ensure a most basic swelling degree. The proton exchange membrane has proper swelling degree, thereby ensuring that the proton exchange membrane has high dimensional stability and high proton conductivity. It is understood that in this application, H is the thickness of the proton exchange membrane after soaking in a water bath environment at 25 ℃ for 10 minutes (at this time, the proton exchange membrane is considered to have fully absorbed water and swelled, i.e. the proton exchange membrane is in a saturated wet state).
If the swelling value is too large (greater than 1.5), the deformation degree of the proton exchange membrane before and after infiltration is relatively high, and the local stress of the proton exchange membrane is increased in the process of continuous swelling and dehydration of the proton exchange membrane, so that the probability of mechanical damage of the proton exchange membrane is increased, and the service life of the proton exchange membrane is reduced. Further, too high a degree of deformation of the proton exchange membrane may also cause deformation of the electrodes of the proton exchange membrane fuel cell, thereby causing degradation of the cell performance. If the swelling value is too small (less than 0.2), it is explained to a certain extent that the space reserved in the support layer for swelling the first exchange layer and the second exchange layer into the support layer is too large or means that the Ew of the ion exchange material is too large to a certain extent, that is, the ion exchange material filled in the support layer may be relatively too small, the proton conductivity of the proton exchange membrane is relatively low, and further, the output power of the proton exchange membrane fuel cell cannot be ensured.
In conclusion, the proper compactness coefficient I of the proton exchange membrane ensures that the swelling value D of the proton exchange membrane is not too low, and under the combined action of the proper compactness coefficient I and the proper quality and thickness of the supporting layer in unit area, the swelling value D of the proton exchange membrane is not too high, so that the proton exchange membrane is ensured to have higher proton conductivity and higher dimensional stability (service life).
Optionally, the thickness h of the support layer in the dry state p Thickness H in dry state with the proton exchange membrane Dry The ratio is 0.3-0.6.
By using the above techniqueIn the dry state, the thickness h of the supporting layer p Thickness H with proton exchange membrane Dry Has a proper ratio, the thickness of the combined proton exchange membrane is not more than 17 mu m, and the support layer has a proper thickness (h p 2-8 μm), it is indicated that for the proton exchange membrane, the support layer and the ion exchange layers (the first exchange layer and the second exchange layer) have a proper ratio, and it is further indicated that after the proton exchange membrane swells in water, the deformation amount of the proton exchange membrane is not too high compared with the dry film state, i.e. the dimensional stability of the proton exchange membrane is further ensured.
If the ratio of the two is too large (h p :H Dry Greater than 0.6), which means that the thickness of the support layer is relatively too high, while the thickness of the proton membrane as a whole is too small (i.e., the thickness of the first and second exchange layers as a whole is too small), i.e., the content of ion exchange material in the proton exchange membrane is relatively small, and in particular the content of ion exchange material in the support layer is relatively small, which means that the proton exchange membrane has high dimensional stability, but the proton conductivity of the proton exchange membrane is reduced by a small content of ion exchange material, which results in a reduction in the output power of the fuel cell. Further, research and development personnel are also performing research on proton exchange membranes with high-thickness support layers, for example, when preparing proton exchange membranes with higher-thickness support layers, ion exchange materials with smaller Ew values are adopted, and although the ion exchange materials in the proton exchange membranes are relatively less, the Ew of the ion exchange materials is small, so that the proton exchange membranes still have relatively higher proton conductivity. However, the proton exchange membrane has certain disadvantages, and the ion exchange material with relatively better quality (relatively higher content of ion exchange groups) of the proton exchange membrane often means that the proton exchange membrane has better water absorption swelling performance and has limited effect on improving the dimensional stability of the proton exchange membrane. At the same time, higher quality ion exchange materials also mean higher costs in the actual production process.
If the ratio of the two is too small (h p :H Dry < 0.3), indicating that the thickness of the support layer is relatively too small, while the thickness of the proton membrane as a whole is too large (i.e., the first exchange layer,The thickness of the second exchange layer is too large), the thickness of the support layer is small, meaning that the space for swelling of the ion exchange material inside the support layer is relatively limited, while the thickness of the first exchange layer and the second exchange layer is large, meaning that the swelling amplitude of the first exchange layer and the second exchange layer is relatively large. The swelling amplitude of the ion exchange material is large, and the space for the ion exchange material to swell in the support layer is small, which means that the whole deformation degree of the proton exchange membrane is relatively high, and the dimensional stability of the proton exchange membrane is poor.
Optionally, the water content Q of the proton exchange membrane in a saturated and wet state is 0.1-0.45, preferably 0.15-0.45, and is calculated by the following formula: q= (M 1 -M 0 )/M 0 Wherein M is 1 The mass of the proton exchange membrane in unit area in the saturated wetting state is as follows: g.
M 1 in a saturated wet state, a unit area (1 m 2 ) The mass of the proton exchange membrane; m is M 0 In a dry state, a unit area (1 m 2 ) The mass of the proton exchange membrane of (2), the difference (M 1 -M 0 ) I.e. saturated wet state, per unit area (1 m 2 ) The mass of the moisture contained in the proton exchange membrane. The water content (water content) in the proton exchange membrane has a great influence on the conductivity of the proton exchange membrane, and the higher the water content is, the higher the proton conductivity in the proton exchange membrane is, and the membrane resistance is reduced, namely the proton conductivity of the proton exchange membrane is increased.
Of course, the water content of the proton exchange membrane cannot be too high (for example, higher than 0.45), if the water content of the proton exchange membrane is too high, this means that the content of the ion exchange material used for absorbing water in the proton exchange membrane is too high or the mass of water in the water storage holes in the proton exchange membrane is too high (the number of the water storage holes is too large and the volume is too large), if the content of the ion exchange material is too high, the deformation degree of the whole proton exchange membrane is relatively too high after the proton exchange membrane absorbs water and swells, and the proton exchange membrane is easily damaged under continuous swelling and dehydration. Meanwhile, the water content of the proton exchange membrane is too high, which means that the water content in the fuel cell is too high, so that flooding failure of the fuel cell is easy to occur, and the output power of the proton exchange membrane is reduced. If the mass of water in the water storage hole is too much, the water storage hole cannot conduct protons, so that the number of open circuits in the proton exchange membrane is relatively large, and the proton conductivity of the proton exchange membrane is low.
Meanwhile, the water content of the proton exchange membrane cannot be too low (for example, lower than 0.1), if the water content of the proton exchange membrane is too low, it means that the Ew of the ion exchange material in the proton exchange membrane is too high and/or the content of the ion exchange material in the proton exchange membrane is too low, in either case, the proton conductivity of the whole proton exchange membrane is too low, thereby reducing the output power of the proton exchange membrane.
In conclusion, the proton exchange membrane has proper water content, which means that the proton exchange membrane has proper ion exchange material, thereby ensuring high proton conductivity of the proton exchange membrane in practical use. Meanwhile, the water storage holes with proper content are formed in the support layer of the proton exchange membrane, so that the water content of the proton exchange membrane is further ensured, and the water storage holes endow the ion exchange material with a certain swelling space, so that the proton exchange membrane still has higher dimensional stability.
Optionally, the thickness of the first exchange layer and the second exchange layer are substantially consistent, and the equivalent weight Ew of the ion exchange material is not higher than 1600.
By adopting the above technical solution, the thicknesses of the first exchange layer and the second exchange layer are substantially uniform, specifically, the difference between the thicknesses of the first exchange layer and the second exchange layer is not higher than 1.5 μm, preferably not higher than 1 μm, and more preferably not higher than 0.8 μm.
On the basis that the proton exchange membrane and the supporting layer have proper thicknesses and proper ratio is achieved between the thicknesses of the proton exchange membrane and the supporting layer, the thickness of the first exchange layer is basically consistent with that of the second exchange layer, the first exchange layer and the second exchange layer of the proton exchange membrane are provided with proper thicknesses, the degree of dimensional deformation of the first exchange layer and the second exchange layer after water absorption swelling cannot be too high, meanwhile, the supporting layer is internally provided with proper number of water storage holes, and the water storage holes are reserved for a certain swelling space of the ion exchange materials of the first exchange layer and the second exchange layer, so that the dimensional stability of the proton exchange membrane is further guaranteed.
In the present application, the high proton conductivity of the proton exchange membrane is further ensured by controlling the equivalent weight Ew of the ion exchange material to be not higher than 1600g. In this application, the equivalent weight Ew of the ion exchange material is the grams of polymer per mole of ionic acid functional groups, e.g., the ion exchange material is a perfluorosulfonic acid resin (nafion), then the ionic acid functional groups are sulfonic acid groups, and Ew is no higher than 1600, meaning that the mass of the perfluorosulfonic acid resin comprising 1 mole of sulfonic acid groups is no more than 1600g.
Optionally, the intermediate layer includes intermediate layer fibers, the intermediate layer fibers are connected to form a three-dimensional network structure of the intermediate layer, and the SEM average diameter of the intermediate layer fibers is 30-200nm.
By adopting the technical scheme, the middle layer is composed of middle layer fibers with proper average diameters (thickness), and the diameters of the middle layer fibers comprise two parts: support layer fibers and ion exchange material attached to the support layer fibers.
If the diameter of the intermediate layer fibers is too small (e.g., less than 30 nm), this may be indicative of too small support layer fibers and/or too little ion exchange material attached to the support layer fibers. Too fine fibers of the support layer mean that the overall mechanical properties of the intermediate layer are also relatively low, which can result in a proton exchange membrane with low dimensional stability; too little ion exchange material attached to the fibers of the support layer means that the proton conductivity of the proton exchange membrane as a whole is not high.
If the diameter of the middle layer fiber is too thick (for example, greater than 200 nm), which means that the supporting layer fiber is too thick and/or the ion exchange material attached to the supporting layer fiber is too much, the middle layer fiber is too thick, which means that the number of the middle layer fibers is relatively small, even if each middle layer fiber is attached with the ion exchange material, the number of the 'paths' for proton conduction in the middle layer is relatively small, and the proton conductivity of the whole proton exchange membrane is low; too much ion exchange material attached to the fibers of the middle layer means that the deformation amount of the proton exchange membrane is relatively large when the proton exchange membrane swells by absorbing water, and the dimensional stability of the proton exchange membrane is not high.
To sum up, the unit area (1 m 2 ) The middle layer of the proton exchange membrane has proper quality and thickness, the middle layer has middle layer fibers with proper thickness, and the inside of the middle layer has proper filling quantity with a compact coefficient, so that the whole proton exchange membrane is further ensured to have higher dimensional stability and higher proton conductivity.
It will be appreciated that in measuring the diameter of the intermediate fibre, the cross-section of the proton exchange membrane may be first characterised by scanning electron microscopy to obtain a corresponding SEM image and selecting an area, for example 100 μm 2 (10 μm by 10 μm) or 25 μm 2 (5 μm by 5 μm), the specific area size is determined according to the actual situation, the diameters of all the intermediate layer fibers on the area are measured by corresponding computer software or manually, and the average value is calculated, so that the average diameter of the intermediate layer fibers of the section is obtained; the person skilled in the art can also obtain the above parameters by other measuring means, which are provided for reference only.
Optionally, the SEM average diameter of the interlayer fibers and the thickness h of the interlayer in the dry state p The ratio is 5-50nm/μm, preferably 7-35nm/μm.
By adopting the technical scheme, the SEM average diameter of the interlayer fiber and the thickness h of the interlayer in a dry state p If the ratio of the two is too small, the support layer fibers are relatively thin, the ion exchange materials attached to the support layer fibers are relatively less, the ion conduction capacity is relatively weak, meanwhile, the middle layer is relatively thick, the path for proton conduction in the proton exchange membrane is relatively long, the internal resistance of the proton exchange membrane is high, and the proton conductivity of the proton exchange membrane is low under the combined action of the two.
If the ratio of the two is too large, the middle layer fibers are relatively thick, and if the middle layer fibers are relatively thin, on the premise that the mass and the thickness of the middle layer in unit area are determined (the mass and the volume of a solid part are determined), the number of the middle layer fibers is relatively small, the number of 'paths' for proton conduction in the middle layer is relatively small, and the proton conductivity of the whole proton exchange membrane is low. If the ion exchange material attached to the fibers of the support layer is relatively excessive and the middle layer is thinner, the deformation amount of the proton exchange membrane when the proton exchange membrane absorbs water and swells is relatively large, and the dimensional stability of the proton exchange membrane is not high.
To sum up, the unit area (1 m 2 ) The intermediate layer of the proton exchange membrane has proper mass and thickness, the intermediate layer has intermediate layer fibers with proper thickness, the interior of the intermediate layer has proper filling quantity with a compaction coefficient, and further, the SEM average diameter of the intermediate layer fibers and the thickness h of the intermediate layer in a dry state p The proton exchange membrane has proper ratio, and under the combined action of the characteristics, the whole proton exchange membrane is further ensured to have higher dimensional stability and higher proton conductivity.
Optionally, the intermediate layer is provided with a plurality of nodes, each node is formed by mutually stacking and fusing a plurality of intermediate layer fibers, and the SEM average diameter of the nodes is 100-600nm.
By adopting the technical scheme, the middle layer is internally provided with a plurality of nodes, and the nodes have a certain reinforcing effect on the integral mechanical property of the middle layer. The diameter of node can not be too thin (for example be less than 100 nm) to guarantee the reinforcement effect of node to the intermediate layer, further guarantee that proton exchange membrane can not surpass the damage threshold value in the deformation volume of swelling that absorbs water, make proton exchange membrane possess higher dimensional stability, thereby guarantee that the proton exchange membrane of this application possesses better life. Meanwhile, the diameter of the node is not too thick (such as more than 500 nm), the too thick node means stronger reinforcing effect on the whole middle layer, but when the middle layer is filled with the ion exchange material, the too thick node can form relatively larger resistance to the ion exchange material, the too thick node can also cause certain loss of pore space in the middle layer, and under the combined action of the two, the filling amount of the ion exchange material in the middle layer is relatively smaller, and the proton conductivity of the proton exchange membrane is lower.
To sum up, the unit area (1 m 2 ) The intermediate layer has the quality and thickness, the intermediate layer fiber with proper thickness and the node with proper thickness, the intermediate layer is ensured to have enough self-supporting performance, and the deformation amount of the whole proton exchange membrane is not too high. Meanwhile, the middle layer is ensured to have enough space for filling with the ion exchange material, after the ion exchange material fills the middle layer, water storage holes with proper quantity and volume are still formed in the middle layer, the introduction of the water storage holes further reduces the deformation of the proton exchange membrane, the deformation of the proton exchange membrane is further controlled in a smaller range, the deformation of the proton exchange membrane cannot exceed a damage threshold value, and the proton exchange membrane has higher dimensional stability, so that the proton exchange membrane has better service life. The damage threshold is the maximum deformation that can be tolerated before damage to the proton exchange membrane occurs. Meanwhile, the introduction of the water storage holes also increases the proton conductivity of the proton exchange membrane.
Optionally, the ratio of the SEM average diameter of the interlayer fibers to the SEM average diameter of the nodes is from 0.2 to 0.4nm/nm.
By adopting the technical scheme, the diameters of the middle layer fiber and the nodes are provided with proper ratio, if the ratio of the diameters is too small, the middle layer fiber is relatively too thick and the nodes are relatively too thin, the reinforcing effect of the nodes on the middle layer fiber (middle layer) is not obvious, if the ratio of the diameters is too large, the middle layer fiber is relatively too thin and the nodes are relatively too thick, the middle layer fiber is too thin, and even if the reinforcing effect of the middle layer exists, the mechanical performance of the middle layer may still be insufficient. The middle layer is provided with middle layer fibers and nodes with proper thickness, proper ratio is provided between the middle layer fibers and the nodes, proper mechanical strength of the middle layer is further ensured, and the middle layer is matched with ion exchange materials (with water storage holes with certain quantity and volume) with proper content, so that the proton exchange membrane is further ensured to have higher dimensional stability and higher proton conductivity.
Optionally, the area ratio of the holes on the cross section of the middle layer is 8% -30%.
The cross section of the middle layer has proper hole area rate, and further demonstrates the proper filling amount of the ion exchange material in the middle layer. The water storage holes with proper hole area ratio endow the proton exchange membrane with certain water storage and water retention functions, reduce water permeation resistance, improve water distribution uniformity, ensure that the proton exchange membrane has relatively good wetting everywhere, thereby ensuring that the proton exchange membrane can be completely wetted under the condition of low water content (under the working conditions of normal humidity and high humidity, the fuel cell can not be flooded), and ensure that the proton membrane can be fully wetted under the high-temperature and low-humidity environment), namely the middle layer has the water storage holes with proper hole area ratio, and the proton exchange membrane has high proton conductivity under various working conditions (normal working conditions and limit working conditions);
due to the fact that per unit area (1 m 2 ) The proton membrane of the (2) has an intermediate layer with proper quality, thickness and compactness, and proper mechanical properties are endowed to the proton exchange membrane. Meanwhile, the section of the middle layer is provided with a proper hole area, the hole structure provides a certain swelling space for the ion exchange material, and under the combined action of the hole area and the ion exchange material, part of the ion exchange material can swell into the middle layer, so that the deformation amount generated when the proton exchange membrane absorbs water and swells is relatively small, namely the proton exchange membrane has higher dimensional stability.
In a second aspect, the present application provides a process for preparing a proton exchange membrane, which adopts the following technical scheme:
s1, preparing an ion exchange resin solution; the ion exchange resin solution comprises the following raw materials: ion exchange materials and solvents; the solid content in the ion exchange resin solution is 5-30%, preferably 8-28%;
s2, coating; coating an ion exchange resin solution on one side of a carrier, covering a supporting layer above the ion exchange resin solution, contacting the lower layer of the supporting layer with the ion exchange resin solution, and then coating the ion exchange resin solution above the supporting layer to obtain a composite membrane; the ion exchange resin solution permeates into the supporting layer to form primary migration;
s3, preprocessing; drying the composite membrane, wherein the drying temperature is 15-25 ℃ higher than the temperature of the ion exchange resin solution, the pretreatment time is 5-25min, and the raw membrane is obtained after the pretreatment; in the pretreatment process, the ion exchange material secondarily migrates to the surfaces of the two sides of the membrane;
s4, drying at a high temperature; and (3) placing the raw membrane in an environment of 120-160 ℃ for drying, and obtaining the proton exchange membrane after the raw membrane is dried.
When the proton membrane is prepared, the first step is the preparation of an ion exchange resin solution, and the ion exchange resin solution has proper solid content (the solid content refers to the mass ratio of an ion exchange material in the ion exchange resin solution) by controlling the ion exchange resin solution, so that the ion exchange resin solution has proper viscosity and fluidity, and is convenient for the subsequent coating and drying steps.
The second step of the application is a coating step, and after the coating is completed, both sides of the supporting layer are provided with ion exchange resin solution with a certain thickness. Further, the ion exchange resin solution having a suitable viscosity and fluidity is permeated into the pore structure inside the support layer and is filled in the support layer, that is, the ion exchange resin solution as a whole is once migrated into the pore structure inside the support layer.
The third step of the present application is a pretreatment step, in the drying process of the composite membrane in the environment of 25-45 ℃, the solvent of the ion exchange resin solution (especially the solvent on the two sides of the composite membrane) will evaporate to a certain extent, the closer to the two sides of the composite membrane, the higher the solid content of the ion exchange resin solution (concentration) gradient between the two sides of the support layer and the interior of the support layer becomes, and it is considered that the solute in the solution will diffuse from high concentration to low concentration, that is, the ion exchange material will diffuse from the two sides of the support layer to the interior of the support layer, however, the inventor of the present application found that in actual production, the ion exchange material in the interior of the support layer will migrate to the two sides of the support layer, so that the finally formed proton exchange membrane has a certain amount and volume of pore structures (water storage holes) in the interior of the support layer, which is quite unexpected.
This is probably because, after the solvent portion of the ion exchange resin solution on both sides of the support layer volatilizes, the solid content of the ion exchange resin solution on both sides of the support layer becomes high, so that the surface tension of the ion exchange resin solution on both sides of the support layer becomes large. Compared with the ion exchange resin solutions at two sides of the supporting layer, the surface tension of the ion exchange resin solutions in the supporting layer is relatively small, the ion exchange resin solutions at two sides of the supporting layer can enable the ion exchange materials in the supporting layer to migrate to two sides of the supporting layer, the influence of the traction on the ion exchange materials is larger than the influence of the concentration gradient on the ion exchange materials, and finally the ion exchange materials in the supporting layer migrate to the surfaces at two sides of the supporting layer. In the pretreatment process, the ion exchange materials in the ion exchange resin solution migrate to the two side surfaces of the supporting layer for the second time, so that the finally formed proton exchange membrane has a certain amount and volume of pore structures.
Further, for the ion exchange material being a fluorine-containing organic material, the fluorine-containing organic material migrates to both side surfaces of the support layer when heated during the pretreatment. After the ion material in the supporting layer migrates, the water storage holes with proper quantity and space are formed in the finally formed proton exchange membrane.
In order to ensure that the ion exchange material inside the support layer can migrate to a suitable extent, the temperature in the pretreatment step must not be too low and the time must not be too short. If the temperature of the pretreatment is too low and the time is too short (less than 30 ℃ and less than 5 minutes), the solvent of the ion exchange resin solution may not be evaporated enough, so that the ion exchange material is not migrated with enough driving force and is migrated with enough time, the number of water storage holes in the finally formed proton exchange membrane is too small and the volume is too small, and the proton conductivity and the dimensional stability of the proton exchange membrane are low; if the pretreatment temperature is too high and the pretreatment time is too long (higher than 45 ℃ and higher than 25 min), the ion exchange material can be excessively migrated, so that the number of water storage holes in the finally formed proton exchange membrane is too large, the volume is too large, the 'open circuit' in the proton exchange membrane is too large, and the proton conductivity is low.
After a pretreatment process at a suitable temperature for a suitable time, the ion exchange material within the support layer has migrated to a suitable extent. The next step is to dry the green film in a high temperature environment of 120-160 ℃, which results in an increase in the migration rate of the ion exchange material, but the ion exchange material is dried and cured in a shorter time in a high temperature environment of 120-160 ℃, and at this time, the ion material in the support layer does not migrate too much.
In summary, the solid content of the ion exchange resin solution is controlled, so that the ion exchange resin solution has proper viscosity and fluidity, and the ion exchange material is ensured to enter the support layer relatively and sufficiently, so that the finally formed proton exchange membrane has proper proton conductivity. Furthermore, the low-temperature pretreatment step and the high-temperature drying step are adopted, so that the ion exchange material with proper content in the support layer migrates to the two sides of the support layer, and the pore structure (water storage hole) with proper quantity and proper volume in the proton exchange membrane is ensured, so that the finally formed proton exchange membrane is further ensured to have proper proton conductivity and dimensional stability.
Optionally, the step S2 specifically includes coating an ion exchange resin solution on one side of a carrier, covering a stretched support layer above the ion exchange resin solution, contacting the lower layer of the support layer with the ion exchange resin solution for 2-10S, and then coating the ion exchange resin solution above the support layer to obtain a composite membrane; the stretching amplitude of the supporting layer is 10-30%.
By adopting the technical scheme, before the supporting layer is covered on the ion exchange resin solution, the supporting layer is stretched, and the stretching amplitude is 10-30%; the inventors of the present application have unexpectedly found that stretching the support layer by an amount of 10-30% before it is covered with the ion exchange resin solution can further ensure that the proton exchange membrane has a pore structure (water storage pores) of a suitable number and volume inside.
This is probably because the inventors of the present application found that the pores of the support layer were first reamed to a small extent as the stretching amplitude of the support layer was stretched, whereas the pore structure in the support layer was instead reduced to a certain extent as the stretching amplitude of the support layer was gradually increased.
In this application, the support layer is stretched by more than 10% before it is covered with the ion exchange resin solution, and the pore size of the internal pores of the support layer is relatively small compared to a conventional tensioned support layer. After the supporting layer is covered with the ion exchange resin solution, the ion exchange resin solution basically fills the holes in the supporting layer, and as the supporting layer slowly recovers deformation, i.e. the holes in the supporting layer slowly grow, a part of space which is not filled by the ion exchange resin solution is increased in the supporting layer. Meanwhile, as the upper layer of the supporting layer is not covered with the ion exchange resin solution, air enters the supporting layer from the upper layer of the supporting layer, and the air is further prevented from filling a plurality of spaces by the ion exchange resin solution, so that a proper number of pore structures (water storage holes) with proper volumes are further ensured in the finally formed proton exchange membrane. Meanwhile, the ion exchange resin solution has proper viscosity and solid content, so that the ion exchange material is not easy to permeate into the pore structure (water storage holes) after the support layer is covered with the ion exchange resin solution for the last time.
Under the synergistic effect of the stretching step and the low-temperature pretreatment step (ion exchange material migration), the proton exchange membrane is further ensured to have a pore structure (water storage holes) with proper quantity and proper volume. Of course, in order to ensure that the support layer is not damaged by excessive stretching, and in order to ensure that the number of water storage holes in the finally formed proton exchange membrane is not excessive, the volume is not excessive, and the stretching amplitude of the support layer is not excessive (more than 30%).
Optionally, in the step S2, the thickness of the ion exchange resin solution above the supporting layer is greater than the thickness of the ion exchange resin solution below the supporting layer, and the ratio of the thickness of the ion exchange resin solution above the supporting layer to the thickness of the ion exchange resin solution below the supporting layer is 0.9-1.2.
By adopting the technical scheme, the thickness of the ion exchange resin solution above the supporting layer is in proper thickness ratio with the ion exchange solution below the supporting layer, so that the thickness of the first exchange layer and the second exchange layer of the finally formed proton exchange membrane is basically consistent.
Optionally, in the step S1, the solvent includes deionized water and an alcohol solvent, where a mass ratio of the deionized water to the alcohol solvent is 0.2-1, and the alcohol solvent is at least one of ethanol, propanol, and isopropanol.
The specific solvent system further ensures that the ion exchange material has a suitable viscosity, thereby further ensuring penetration of the ion exchange resin solution into the support layer. And secondly, the specific solvent volume is combined with the specific pretreatment step, so that the change of the solid content of the ion exchange resin solution is more conveniently controlled, the surface tension of the ion exchange resin at two sides of the base film and the surface tension of the ion exchange resin in the base film are further controlled to have proper gradients, the migration quantity of the ion exchange material is further controlled, and the finally formed proton exchange film is further ensured to have a proper number of pore structures (water storage holes) with proper volumes.
The following beneficial effects can be brought through this application: the proton exchange membrane and the preparation method for preparing the proton exchange membrane, provided by the application, have higher proton conductivity and higher dimensional stability under the working condition of normal humidity or under the special working conditions of high humidity, high temperature, low humidity and the like. Furthermore, the preparation method provided by the invention can conveniently, rapidly and effectively prepare and obtain the proton exchange membrane.
Drawings
FIG. 1 is a schematic view of a Scanning Electron Microscope (SEM) of a cross section of a proton exchange membrane prepared in example 1, with a magnification of 5000X;
FIG. 2 is a schematic view of a Scanning Electron Microscope (SEM) of a cross section of a proton exchange membrane prepared in example 3, with a magnification of 5000X;
FIG. 3 is a schematic view of a Scanning Electron Microscope (SEM) of a cross section of a proton exchange membrane prepared in comparative example 1, with a magnification of 5000X;
Detailed Description
Example 1
The embodiment of the application discloses a proton exchange membrane, which is prepared by the following process steps:
s1, preparing raw materials; the raw materials comprise an ion exchange resin solution and a supporting layer, wherein the ion exchange resin solution comprises the following raw materials: ion exchange materials and solvents; the ion exchange material is specifically perfluorinated sulfonic acid resin, the solvent is deionized water and alcohol solvent, and the mass ratio of the deionized water to the alcohol solvent is 0.6; the alcohol solvent is ethanol; the supporting layer is a PTFE film; the solid content of the ion exchange resin solution is 18.2 weight percent, and the Ew of the ion exchange material is 1124g;
s2, coating; coating an ion exchange resin solution on one side of a carrier, covering a supporting layer above the ion exchange resin solution, contacting the lower layer of the supporting layer with the ion exchange resin solution for 6s, and coating the ion exchange resin solution above the supporting layer to obtain a composite membrane; stretching the support layer before the support layer is covered on the ion exchange resin solution, wherein the stretching amplitude is 20%;
S3, preprocessing; pre-drying the composite film in an environment with the temperature of 30 ℃ for 12min to obtain a green film after pre-drying;
s4, drying at a high temperature; and (5) drying the raw membrane in an environment of 140 ℃ to obtain the proton exchange membrane after drying the raw membrane.
Example 2-example 7
Examples 2-7 differ from example 1 in the solids content of the ion exchange resin solutions and the various process parameters, as detailed in Table 1.
Table 1 solids content of ion exchange resin solutions of examples and process parameters
Comparative example 1:
the proton exchange membrane of comparative example 1 was prepared using the following process steps:
s1, preparing an ion exchange resin solution; the ion exchange resin solution comprises the following raw materials: ion exchange materials and solvents; the ion exchange material is specifically perfluorinated sulfonic acid resin, the solvent is deionized water and alcohol solvent, and the mass ratio of the deionized water to the alcohol solvent is 0.6; the alcohol solvent is ethanol; the supporting layer is a PTFE film; the solid content in the ion exchange resin solution was 18.7wt%; the Ew of the ion exchange material is 1153g;
s2, coating; coating an ion exchange resin solution on one side of a carrier, covering a supporting layer above the ion exchange resin solution, and then coating the ion exchange resin solution above the supporting layer to obtain a composite membrane;
S3, drying at a high temperature; drying the raw membrane in an environment of 170 ℃ to obtain a proton exchange membrane;
and S4, repeating the steps of S2 coating and S3 high-temperature drying until the proton exchange membrane is basically transparent, and considering that the supporting layer of the proton exchange membrane is completely filled.
Comparative example 2:
the proton exchange membrane of comparative example 2 was prepared using the following process steps:
s1, preparing an ion exchange resin solution; the ion exchange resin solution comprises the following raw materials: ion exchange materials and solvents; the ion exchange material is specifically perfluorinated sulfonic acid resin, the solvent is deionized water and alcohol solvent, and the mass ratio of the deionized water to the alcohol solvent is 0.6; the alcohol solvent is ethanol; the supporting layer is a PTFE film; the solid content in the ion exchange resin solution was 17.6wt%; the Ew of the ion exchange material is 512g;
s2, primary coating and drying; coating an ion exchange resin solution on one side of a carrier to obtain a first composite membrane, and then drying the first composite membrane in an environment of 165 ℃ to obtain a green membrane;
s3, secondary coating and drying; coating an ion exchange resin solution on the other side of the carrier to obtain a second composite membrane, and then drying the second composite membrane in an environment of 165 ℃ to obtain a proton exchange membrane;
And S4, repeating the steps of S2 coating and S3 high-temperature drying until the proton exchange membrane is basically transparent, and considering that the supporting layer of the proton exchange membrane is completely filled.
Performance detection and data
The detection method comprises the following steps:
proton conductivity: proton exchange membranes prepared in each of examples and comparative examples were used as a sample for proton conductivity measurement, and the measurement method was described in GB/T20042.3-2022.
Ew: the proton exchange membranes prepared in each of examples and comparative examples were used as a sample for ion exchange Equivalent (EW) test, wherein the detection method was described in GB/T20042.3-2022.
The morphology parameters and the performance parameters of the proton exchange membranes prepared in each example and comparative example are shown in tables 2 and 3 in detail:
TABLE 2 proton exchange Membrane morphology and Performance parameters
Remarks:
proton conductivity (1) is the proton conductivity of the proton exchange membrane at 25 ℃ and 40%RH; proton conductivity (2) is the proton conductivity of the proton exchange membrane at 80 ℃,30% rh.
TABLE 3 Cross-sectional morphology parameters of support layers in proton exchange membranes
Conclusion:
by comparing example 1 with comparative example 1, it is readily found that the Ew of the ion exchange material of comparative example 1 is smaller and the loading of the ion exchange material in the support layer of comparative example 1 is much higher than in example 1. The expected effect is that the proton conductivity of comparative example 1 is higher than that of example 1. However, under specific working conditions (high temperature and low humidity), the proton conductivity of comparative example 1 is far lower than that of example 1, which is probably because a certain number of water storage holes exist in the supporting layer of the proton exchange membrane provided in example 1, the water storage holes endow the proton exchange membrane with certain water storage and water retention functions, reduce water permeation resistance, improve water distribution uniformity, enable the proton exchange membrane to be relatively well wetted everywhere, and ensure that water in the proton exchange membrane is not easy to volatilize, so that the proton exchange membrane of example 1 can also have higher proton conductivity under the working conditions of high temperature and low humidity. On the one hand, the (fully filled) proton membrane provided in comparative example 1 has more ion exchange material in the supporting layer, so that the proton exchange membrane needs more moisture to be fully wetted, but the proton membrane with high moisture requirement cannot obtain sufficient moisture due to the drier air environment, so that the proton exchange membrane is difficult to be fully wetted; on the other hand, because the support layer of the proton exchange membrane lacks a hole structure with water retention and water storage functions, under the environment that the air environment is dry and the air temperature is relatively high, the permeation resistance of water is large and the water is more easily volatilized, so that the proton exchange membrane is difficult to sufficiently wet, the actual proton conductivity of the proton exchange membrane is not high, and the output power of the battery is lower.
By comparing example 1 with comparative example 2, it was otherwise found that the thickness of the proton exchange membrane of comparative example 2 was substantially similar to that of example 1, while the support layer thickness of the proton exchange membrane of comparative example 2 was much greater than that of example 1, with the expected effect that the dimensional stability of comparative example 2 was higher than that of example 1. However, in practical use, the dimensional stability of comparative example 2 is far lower than that of example 1, which is probably because the proton exchange membrane must absorb a certain amount of moisture (wet) during operation, and the swelling of the ion exchange material by water absorption is a certain phenomenon, and the support layer of the proton exchange membrane of example 1 has a certain water storage hole therein, and this part of hole structure provides a certain swelling space for the ion exchange material, that is, part of the ion exchange material can swell into the support layer, so that the deformation amount generated when the proton exchange membrane absorbs water and swells is relatively small, and the proton exchange membrane has higher dimensional stability.
The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above examples, and all technical solutions belonging to the concept of the present invention belong to the protection scope of the present invention. It should be noted that modifications and adaptations to the present invention may occur to one skilled in the art without departing from the principles of the present invention and are intended to be within the scope of the present invention.
Claims (14)
1. A proton exchange membrane, comprising a main body, and characterized in that the main body comprises a first exchange layer, an intermediate layer and a second exchange layer, wherein the first exchange layer is provided with a compact first outer surface, the second exchange layer is provided with a compact second outer surface, the first exchange layer and the second exchange layer are both prepared from ion exchange materials, and the intermediate layer comprises a support layer, the ion exchange materials partially filled in the support layer and water storage holes positioned in the support layer;
thickness H of the proton exchange membrane in a dry state Dry Not higher than 17 μm;
the compactness coefficient I of the proton exchange membrane is 0.15-0.65, and is obtained through the following formula: i=m n /(m n +m P ) X 100%, where m n In dry state, the mass of the ion exchange material in the unit area interlayer is as follows: g; m is m P The mass of the supporting layer in unit area in the dry state is as follows: g;
m n calculated by the following formula: m is m n ＝M 0 -(m P +ρ n V n ) Wherein M is 0 The mass of the proton exchange membrane in unit area in the dry state is as follows: g; ρ n In dry state, the ion exchange material has a density in g/m 3 ；V n In dry state, the sum of the volumes of the first exchange layer and the second exchange layer in the proton exchange membrane is expressed as m 3 ；
Mass m of support layer per unit area in dry state P 2-10g; thickness h of support layer in dry state p 2-9 μm, the unit area is 1m 2 。
2. A proton exchange membrane according to claim 1, wherein: the swelling value D of the proton exchange membrane is 0.2-1.5, and the swelling value D is communicatedCalculated by the following formula: d= (H) Moistening device -H Dry )/H Dry Wherein H is Moistening device Is the thickness of the proton exchange membrane in a saturated wetting state after water absorption swelling, and the unit is mu m.
3. A proton exchange membrane according to claim 1, wherein: thickness h of the support layer in the dry state p Thickness H in dry state with the proton exchange membrane Dry The ratio is 0.3-0.6.
4. A proton exchange membrane according to claim 1, wherein: the water content Q of the proton exchange membrane in a saturated wetting state is 0.1-0.45, and the water content Q is calculated by the following formula: q= (M 1 -M 0 )/M 0 Wherein M is 1 The mass of the proton exchange membrane in unit area in the saturated wetting state is as follows: g.
5. a proton exchange membrane according to claim 1, wherein: the first exchange layer and the second exchange layer have a thickness substantially consistent, and the ion exchange material has an equivalent weight Ew of no more than 1600.
6. A proton exchange membrane according to claim 1, wherein: the middle layer comprises middle layer fibers which are connected with each other to form a three-dimensional network structure of the middle layer, and the SEM average diameter of the middle layer fibers is 30-200nm.
7. A proton exchange membrane according to claim 6, wherein: the ratio of the SEM average diameter of the interlayer fibers to the thickness hp of the support layer in the dry state is from 5 to 50nm/μm.
8. A proton exchange membrane according to claim 6, wherein: the interlayer is internally provided with a plurality of nodes, each node is formed by mutually stacking and fusing a plurality of interlayer fibers, and the SEM average diameter of the nodes is 100-600nm.
9. A proton exchange membrane according to claim 8, wherein: the ratio of the SEM average diameter of the middle layer fibers to the SEM average diameter of the nodes is 0.2-0.4.
10. A proton exchange membrane according to claim 1, wherein: the area ratio of the holes on the section of the middle layer is 8% -30%.
11. A process for the preparation of a proton exchange membrane according to any one of claims 1 to 10, comprising the following process steps:
S1, preparing an ion exchange resin solution; the ion exchange resin solution comprises the following raw materials: ion exchange materials and solvents; the solid content in the ion exchange resin solution is 5-30%;
s2, coating; coating an ion exchange resin solution on one side of a carrier, covering a supporting layer above the ion exchange resin solution, and then coating the ion exchange resin solution above the supporting layer to obtain a composite membrane; the ion exchange resin solution permeates into the supporting layer to form primary migration;
s3, drying; drying the composite membrane to obtain a proton exchange membrane; the drying specifically comprises pre-drying and high-temperature drying, wherein in the pre-drying process, the ambient temperature is 30-50 ℃, the pre-drying time is 5-25min, and the ion exchange material secondarily migrates to the surfaces of the two sides of the membrane; in the high-temperature drying process, the ambient temperature is 120-160 ℃.
12. The process for preparing a proton exchange membrane according to claim 11, wherein step S2 is specifically that an ion exchange resin solution is coated on one side of a carrier, a stretched support layer is covered above the ion exchange resin solution, the lower layer of the support layer is contacted with the ion exchange resin solution for 2-10S, and then the ion exchange resin solution is coated above the support layer to obtain a composite membrane; the stretching amplitude of the supporting layer is 10-30%.
13. The process according to claim 11, wherein in the step S2, the thickness of the ion exchange resin solution above the support layer is greater than the thickness of the ion exchange resin solution below the support layer, and the ratio of the thickness of the ion exchange resin solution above the support layer to the thickness of the ion exchange resin solution below the support layer is 0.9-1.2.
14. The process for preparing a proton exchange membrane according to claim 11, wherein in the step S1, the solvent comprises deionized water and an alcohol solvent, wherein the mass ratio of the deionized water to the alcohol solvent is 0.2-1; the alcohol solvent is at least one of ethanol, propanol and isopropanol.
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