US20130087451A1

US20130087451A1 - Membrane Electrode Assembly and Organic Hydride Manufacturing Device

Info

Publication number: US20130087451A1
Application number: US13/645,117
Authority: US
Inventors: Takayuki Hirashige; Takao Ishikawa
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2011-10-06
Filing date: 2012-10-04
Publication date: 2013-04-11
Also published as: KR101417354B1; CN103031565A; KR20130037649A; JP2013084360A

Abstract

There is provided a membrane electrode assembly and an organic hydride manufacturing device capable of obtaining higher energy efficiency even if manufacturing organic hydride in one step with a single device. A membrane electrode assembly in which a cathode catalyst layer and an anode catalyst layer are placed to sandwich a solid polymer electrolyte membrane, wherein the cathode catalyst layer includes catalytic metal which causes hydrogenation of unsaturated hydrocarbons to organic hydrides, and a carrier of the catalytic metal, and the carrier provides on its surface a functional group which decreases wettability of the unsaturated hydrocarbons.

Description

CLAIM OF PRIORITY

The present application claims priority from Japanese patent application JP 2011-221674 filed on Oct. 6, 2011 the content of which is hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a membrane electrode assembly and an organic hydride manufacturing device, for manufacturing organic hydride electrochemically.
2. Description of the Related Art
While global warming by carbon dioxide and the like is getting serious, hydrogen as an energy source responsible for the next generation instead of fossil fuels receives attention. With hydrogen fuels, the only emission during fuel consumption is water, and due to no carbon dioxide emission, the environmental load is low. On the other hand, because hydrogen is a gas at the ordinary temperature and normal pressure, the system of transporting, storing, and supplying it is an important problem.
Recently, an organic hydride system using hydrocarbon like as cyclohexane, methylcyclohexane and decalin is drawing attention as a superior hydrogen storing system in safety, transportability, and storing capacity. Since these hydrocarbons are liquid at ordinary temperature, they are superior in transportability. For example, although toluene and methylcyclohexane are cyclic hydrocarbons having the same carbon number, while toluene is an unsaturated hydrocarbon in which the bonding between the hydrocarbons is a double bond, methylcyclohexane is a saturated hydrocarbon having no double bond. Methylcyclohexane is yielded by the hydrogenation of toluene, and toluene is yielded by the dehydrogenation. Thus, utilizing the hydrogenation and the dehydrogenation of hydrocarbon allows the storage and the supply of hydrogen.
To manufacture organic hydride such as methylcyclohexane, firstly, it is needed to manufacture hydrogen, and then react the hydrogen and toluene on a catalyst. In other words, the current process is a two-stage process in which hydrogen is yielded in water-electrolyzer and the like, and hydrogen and toluene is reacted to yield organic hydride in the hydrogenation device.
Therefore, plural devices are needed toward manufacturing organic hydride, and there occurs a problem called complication of the devices. Furthermore, since hydrogen is a gas until hydrogenation occurs, there occurs a problem on the storage and the transport. If the hydrogen manufacturing device and the hydrogenation device are constructed adjacently, the above-mentioned problem will be solved; however, there is an issue of costs of construction and operation, and the overall energy efficiency is also decreased. Furthermore, since the increasing size of the devices is needed, there is also a problem that the installation location is limited.
Contrary to the two-stage process, the technologies of manufacturing organic hydride in one-stage with only one device has been proposed (for example, Japanese Patent Laid-Open 2003-45449, Catalysis Today, 56, 307 (2000)). They manufacture organic hydride electrochemically. For example, in Japanese Published Unexamined Application No. 2003-45449, organic hydride is manufactured by placing metallic catalysts on the both sides of a hydrogen ion permeable electrolyte membrane, respectively, supplying water or steam on one side and unsaturated hydrocarbon (s) on the other side, and causing the hydrogenation of unsaturated hydrocarbon (s) to saturated hydrocarbon (s) (organic hydride (s)) by hydrogen ion yielded by electrolysis of water or steam. Respective reaction formulae of anode and cathode in the case of using toluene as an unsaturated hydrocarbon are as follows.
H₂O→2H⁺+(½)O₂+2e ⁻ (1)
C₇H₈+6H⁺+6e ⁻→C₇H₁₄ (2)

SUMMARY OF THE INVENTION

With these methods of manufacturing organic hydride, however, it has been difficult to obtain higher energy efficiency.
An object of the present invention is to provide a membrane electrode assembly and an organic hydride manufacturing device capable of obtaining higher energy efficiency even if manufacturing organic hydride in one step with a single device.
One embodiment for achieving the above-mentioned object is a membrane electrode assembly in which a cathode catalyst layer which reduces unsaturated hydrocarbons and an anode catalyst layer which oxides water are placed to sandwich a solid polymer electrolyte membrane which is proton conductive, wherein the cathode catalyst layer includes a catalytic metal which makes an organic hydride by reducing the unsaturated hydrocarbon, a carrier which supports the catalytic metal, and the solid polymer electrolyte membrane which is proton conductive; and a functional group which decreases wettability of the unsaturated hydrocarbon is introduced onto a surface of the carrier.
In addition, it is an organic hydride manufacturing device including the membrane electrode assembly, a member supplying the unsaturated hydrocarbon to the cathode catalyst layer, and a member supplying water or steam to the anode catalyst layer.
Furthermore, it is an organic hydride manufacturing device including a cathode catalyst layer, an anode catalyst layer, and a separator which supplies an unsaturated hydrocarbon to the cathode catalyst layer to remove organic hydride, and supplies H₂O to the anode catalyst layer to evacuate oxygen and water, wherein the cathode catalyst layer is placed on one surface of a solid polymer electrolyte membrane, and the anode catalyst layer is placed on another surface of the solid polymer electrolyte membrane, the cathode catalyst layer includes a catalytic metal which makes an organic hydride by reducing the unsaturated hydrocarbon, and a carrier which supports the catalytic metal, and the carrier has on its surface a functional group which decreases wettability of the unsaturated hydrocarbon.
According to the present invention, by introducing a functional group which decreases wettability of the unsaturated hydrocarbon on the surface of the carrier which supports the catalytic metal, it is possible to provide a membrane electrode assembly and an organic hydride manufacturing device capable of obtaining higher energy efficiency, even if manufacturing organic hydride in one step with a single device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating one example of an organic hydride manufacturing device with relation to an embodiment of the present invention;

FIGS. 2A to 2C are views illustrating a membrane electrode assembly with relation to an embodiment of the present invention; 2A is a plan view, 2B is a D-E cross-sectional view of the plan view, and 2C is an enlarged view of part F of the cross-sectional view;

FIGS. 3A to 3C are views illustrating a membrane electrode assembly of a related art; 3A is a plan view, 3B is a D-E cross-sectional view of the plan view, and 3C is an enlarged view of part F of the cross-sectional view;

FIG. 4 is a view illustrating one example of the relation between current density and applied voltage, in the organic hydride manufacturing device with relation to First Example of the present invention;

FIG. 5 is a view illustrating one example of the relation between conversion rate and applied voltage, in the organic hydride manufacturing device with relation to First Example of the present invention;

FIG. 6 is a view illustrating one example of the relation between current density and applied voltage, in the organic hydride manufacturing device with relation to First Comparative Example;

FIG. 7 is a view illustrating one example of the relation between conversion rate and applied voltage; and

FIG. 8 is a view illustrating one example of current density and conversion rate, in the organic hydride manufacturing device with relation to the first to the third examples of the present invention, and First Comparative Example.

DETAILED DESCRIPTION OF THE INVENTION

The inventors examined the reasons why higher energy efficiency was not obtainable when manufacturing organic hydride in one-stage with the conventional single device. As a result, they found that there was a problem in wettability of unsaturated hydrocarbons such as toluene to electrodes, as one of the reasons. The electrodes of a single organic hydride manufacturing device in one-stage is formed of the layer in which a proton conductive electrolyte is mixed with catalyst, and called as a catalytic layer. Of the catalytic layer, a catalyst includes a carrier supports metallic catalyst such as platinum. The condition like having higher electron conductivity, higher specific surface area to prevent coagulation of metallic catalyst such as platinum and to enhance the dispensability, and the like are needed for the carrier, and carbon-based material is used generally.
However, the wettability of unsaturated hydrocarbons such as toluene to carbon-based material is very strong and easy to become wet. For example, activated carbon is the carbon-based material which has large specific surface area, and it is known that toluene is adsorbed to activated carbon. It was speculated that when the wettability of unsaturated hydrocarbons such as toluene to a carrier carbon was strong, the unsaturated hydrocarbon was covered on the carbon surface of the carrier, and absorbed or stagnated on the carbon surface to inhibit the consecutive supply of unsaturated hydrocarbons to a catalyst. In that case, a catalyst which is not supplied with unsaturated hydrocarbons and does not contribute to reaction appears and the energy efficiency becomes low. Therefore, when the carrier carbon was surface-reformed, and the wettability of unsaturated hydrocarbons such as toluene was decreased, it was found possible to prevent stagnating of unsaturated hydrocarbons on the surface of a catalytic layer and to supply unsaturated hydrocarbons to catalyst stably.
The present invention originated from the basis of the above-mentioned findings, and is able to make surface reforming to introduce a functional group such as a sulfonate group, a hydroxyl group, a carboxylate group and the like in a catalytic carrier in a membrane electrode assembly and an organic hydride manufacturing device, for manufacturing organic hydride electrochemically, and is able to use carbon, as a catalytic carrier, which has been decreased in wettability of unsaturated hydrocarbons such as toluene. In addition, the catalyst which supports metallic catalyst on the carbon, and the catalyst in which a solid polymer electrolyte membrane which is proton conductive is mixed together properly have electrode structures which are formed both sides of a solid polymer electrolyte membrane which is proton conductive. On the electrodes, by applying voltage between anode-cathode in the situation that water or steam is supplied onto the anode side and unsaturated hydrocarbons are supplied onto cathode side, it is possible to cause electrolysis of water on the anode and hydrogenation of unsaturated hydrocarbons on the cathode, followed by producing organic hydride.
Embodiments according to the present invention will be described with figures in detail.
One example of an organic hydride manufacturing device according to an embodiment of the present invention is shown in FIG. 1. An organic hydride manufacturing device of the embodiment is made up by jointing an anode catalyst layer 13 on one surface of a solid polymer electrolyte membrane 12 and a cathode catalyst layer 14 on the other surface of the solid polymer electrolyte membrane 12, and sandwiching integrated membrane electrode assembly (MEA) with a gas diffusion layer 15 and a separator 11 in which a groove as a channel for gas and the like is formed. In addition, a gasket 16 for gas seal is inserted between a pair of the separators 11.
The separator 11 has electroconductivity, and for its quality of material, dense graphite plates, carbon plates into which carbon materials such as graphite and carbon black are molded by resin, as well as metallic materials with superior corrosion resistance such as stainless steel and titanium are desirable. In addition, noble metal plating for the surface of the separator 11 and applying highly corrosion resistant and heat resistant electro-conductive paint and preparing surface treatment are also desirable. A groove which becomes a channel of reactive gas or liquid on the surface opposite to an anode catalyst layer 13 and a cathode catalyst layer 14 of the separator 11 is formed. Water or steam is supplied through the groove channel of the separator 11 on the anode side. Water or steam flowing through the groove channel is supplied via gas diffusion layer 15 to the anode catalyst layer 13. In addition, unsaturated hydrocarbons are supplied onto the separator 11 of the cathode side. Unsaturated hydrocarbons flowing through the groove channel are supplied via gas diffusion layer 15 to a cathode catalyst layer 14. As a method of supplying unsaturated hydrocarbons, liquid unsaturated hydrocarbons may be supplied intact, and/or vaporous unsaturated hydrocarbons making He gas, N₂gas and the like as a carrier may be supplied.
A gas diffusion layer 15 is arranged to supply reactive substances (gas or liquid) supplied into the channel of the separator 11 in planes of catalyst layers, and uses a substrate having gas permeability such as carbon paper or carbon cloth.
The gasket 16 has insulation quality, and has resistance to, especially, hydrogen, unsaturated hydrocarbons, or organic hydride, and may have quality of material which has its less permeability and of which hermeticity can be maintained, including butyl rubber, Viton rubber, EPDM rubber (ethylene-propylene-diene rubber) and the like, for example.
When applying voltage between anode and cathode in the state of supplying water or steam at the anode side and toluene as an unsaturated hydrocarbon at the cathode side, electrolysis of water according to the formula (1) occurs. Proton yielded by electrolysis according to the formula (1) transfers via a solid polymer electrolyte membrane 12 to a cathode catalyst layer 14, and in the cathode catalyst layer, hydrogenation according to the formula (2) occurs and methylcyclohexane which is organic hydride yields.
H₂O→2H⁺+(½)O₂+2e ⁻ (1)
C₇H₈+6H⁺+6e ⁻→C₇H₁₄ (2)
An organic hydride device of the present embodiment makes hydrogenation of unsaturated hydrocarbons electrochemically to yield organic hydride.
FIGS. 2A to 2C show electrode parts of an organic hydride manufacturing device according to the embodiment. FIGS. 2A to 2C show a plan view of MEA where a cathode catalyst layer 22 or an anode catalyst layer 23 on each side of a solid polymer electrolyte membrane is formed seen from the cathode side, a D-E cross-sectional view of the plan view, and an enlarged view of part F of the cross-sectional view, respectively.
As illustrated in the D-E cross-sectional view, the cathode and the anode are formed as dense catalyst layers on and below a solid polymer electrolyte membrane 21. As the cathode catalyst layer 22 is illustrated on the enlarged view, catalytic metal 24 is supported on the carbon (carrier) 25 which is a catalytic carrier. The surface treatment is prepared on the carbon 25, and functional groups 27 are introduced. Thus, unsaturated hydrocarbons such as toluene are difficult to wet to the catalyst, and unsaturated hydrocarbons are supplied stably to the catalyst, without covering the catalytic layer surface with unsaturated hydrocarbons and stagnating. In addition, fugacity of organic hydride yielded by hydrogenation becomes also higher. Furthermore, the number 28 denotes unsaturated hydrocarbons or organic hydride.
The carbons 25 are adhered each other with a solid polymer electrolyte 26. The catalytic metal 24 has a network configuration linked via carbon 25 together, and forms a path for electron required for the reaction of the formula (2). In addition, a solid polymer electrolyte 26 has a linking network configuration as well, and forms a path for proton required for the reaction of the formula (2).
Electrode reaction is conducted at the three-phase interface where the catalytic metal 24 on the carbons 25, a solid polymer electrolyte, and the reactant unsaturated hydrocarbons contact. In the electrode of the embodiment, a path for proton is formed by a solid polymer electrolyte 26, so that the three-phase interface is formed even in the catalytic metal 24 which does not contact directly the solid polymer electrolyte membrane 21, then there is provided a configuration in which many metallic catalysts are able to contribute to the electrode reaction, provided that the solid polymer electrolyte membrane 21 provides a solid polymer electrolyte and it is desirable but not essential for a cathode catalyst layer to comprise solid polymer electrolytes 26.
An electrode part of an organic hydride manufacturing device of a related art is shown in FIGS. 3A to 3C. FIGS. 3A to 3C show a plan view of an MEA where a cathode catalyst layer 32 and an anode catalyst layer are formed on each side of a solid polymer electrolyte membrane 31, part D-part E cross-sectional view of the plan view, and an enlarged view of part F of the cross-sectional view, respectively. On the electrodes in the FIGS. 3A to 3C, unsaturated hydrocarbons cover on the carbon surface of the carrier, and absorb or stagnate on the carbon surface, so that unsaturated hydrocarbons are not supplied, catalysts not contributing to the reaction are generated, and energy efficiency becomes lower. Furthermore, the number 34 denotes catalytic metal, the number 35 denotes carbon carrier, and the number 36 denotes unsaturated hydrocarbons or organic hydride.
The carbon 25, which is a catalytic carrier of the embodiment, is characterized in that the functional groups 27 are introduced by surface reforming. Hereby, unsaturated hydrocarbons become difficult to wet, stagnation of unsaturated hydrocarbons on the surface of a cathode catalyst layer 22 is prevented, and the supply of unsaturated hydrocarbons to the cathode catalyst layer 22 is not inhibited.
Anything is acceptable for the functional groups 27 which are introduced on the carbon surface as long as they decrease wettability of unsaturated hydrocarbons such as toluene and increase oil repellency. For example, they include a sulfonate group, a phosphonate group, a hydroxyl group, a sulfomethyl group, a carboxyl group, a carbonyl group, a carboxylate group and the like. At least one of these may be included, and especially a sulfonate group is practically suitable.
As the carrier 25, anything is acceptable as long as it is electron-conductive carbon. For example, it includes furnace black and channel black, acetylene black, amorphous black, carbon nanotube, carbon nanohorn, carbon black, activated carbon, graphite and the like. These can be used alone or by mixture.
As a method of surface-treating of carbon to introduce functional groups, for example, it is possible to treat carbon with sulfuric gas, fuming sulfuric acid, sulfuric acid and the like to introduce sulfonate groups. In addition, it is possible to treat carbon with sodium sulfite, sodium bisulfite, aqueous formalin solution, paraformaldehyde and the like to introduce a sulfomethyl group. Moreover, it can be considered to irradiate oxygen plasma for the introduction of hydroxyl groups.
On the other hand, a catalytic material causing hydrogenation is used as the catalytic metal 24 used in the present embodiment, metals such as Ni, Pd, Pt, Rh, Ir, Re, Ru, Mo, W, V, Os, Cr, Co, Fe and the like as well as their alloy catalysts, for example, are possible to use, and especially, Pt (platinum), ruthenium (Ru), rhodium (Rh), palladium (Pa), iridium (Ir), molybdenum (Mo), rhenium (Re), wolfram (W) and their alloy are practically suitable. It is preferable to micronized hydrogenation catalysts, for cost reduction by the decrease of catalytic metals, and an increased reaction surface area.
In addition, as a method of supporting the catalytic metal 24 on the carrier carbon 25, there are coprecipitation, thermal decomposition, electroless plating and the like, and have no particular limitation.
The MEA of the embodiment can be prepared by the following method. Firstly, a cathode catalyst paste to which a catalyst with the catalytic metal 24 supported by the surface-treated carbon 25, a solid polymer electrolyte, and a solvent which dissolved a solid polymer electrolyte, is added to mix thoroughly, and an anode catalyst paste where platinum black, a solid polymer electrolyte, and a solvent which dissolved a solid polymer electrolyte are added to mix thoroughly are prepared. Those pastes are sprayed onto release film such as polyfluoroethylene (PTFE) film, with spray-dry method and the like, respectively, and dried at 80° C. to evaporate the solvent to form cathode and anode catalyst layers. Next, those cathode and anode catalyst layers are joined by hot press method with sandwiching the solid polymer electrolyte membrane 21 in the middle, and it is possible to prepare MEA of the embodiment by peeling off the release film (PTFE).
In addition, as another example of MEA preparation of the present embodiment, it is also possible to prepare it by spraying a cathode catalyst paste in which a catalyst with the catalytic metal 24 supported by the surface-treated carbon 25, a solid polymer electrolyte, and a solvent which dissolves a solid polymer electrolyte are added to the above-mentioned surface-treated carbon 25 and mixed thoroughly, and anode catalyst paste in which platinum black, a solid polymer electrolyte, and a solvent which dissolves a solid polymer electrolyte, to the solid polymer electrolyte membrane 21 directly with spray-dry method and the like.
As polymer electrolytes which compose the solid polymer electrolyte membrane 21, perfluorocarbon sulfonate, or materials which have doped or bound chemically and fixed proton donor such as sulfonate groups, phosphonate groups and carboxyl groups to polystyrene, polyether ketone, polyetherether ketone, polysulfone, polyethersulfone or the other engineering plastic materials, can be used. In addition, by transforming the above-mentioned materials to cross-linked structure or fluorinating it partially, the material stability can be enhanced.
For a solid polymer electrolyte contained in a catalytic layer, a polymer material which shows proton conductivity is used, and examples include sulfonated or alkylene-sulfonated fluorine-based polymer and polystyrenes which are represented by perfluorocarbon-based sulfonate resin and polyperfluorostyrene-based sulfonate resin. Further, the materials in which proton donor is introduced to polysulfones polyethersulfones, polyetherethersulfones, polyetherether ketones, or hydrocarbon-based polymer are included. In addition, composite electrolyte of polymer material of the embodiment and metal oxide hydrates can be used.
As an unsaturated hydrocarbon, aromatic hydrocarbon can be used, and for example either of benzene, toluene, xylene, mesitylene, naphthalene, methylnaphthalene, anthracene, biphenyl, phenanthroline and their alkyl substitutes, or a multi-mixture can be used. Hydrogen is added to a double bond of these carbons so that hydrogen can be stored.
In the following, the present invention will be described with examples in detail. However, the present invention is not limited to examples mentioned below.

First Example

As a catalyst, a catalyst where 30 wt % of Pt particulates was dispersed and supported on carbon black was used. Firstly, 100 g of this catalyst was preheated for one hour at 105° C. Subsequently, sulfur trioxide heated to 100° C. was transferred at 12 vol. % of concentration to dry air, and reacted with the catalyst. Reaction time was two hours. Subsequently, it was cooled, the catalyst was submitted to ion exchanged water, stirred and filtrated, and washed with ion exchanged water until pH of the filtrate became constant.
When the infrared absorption spectrum was measured to the obtained catalyst, the peaks were observed at 620 cm⁻¹, 1037 cm⁻¹and 1225 cm⁻¹. This was considered as the peak based on the sulfonate group —SO₃H, and it was confirmed that the sulfonate group was introduced on the surface of the carbon black which was a carrier. The equivalent of the introduced sulfonate group was 1.8 milliequivalent/g dry carbon carrier.
The above-obtained catalyst was used as a cathode catalyst, and MEA, the configuration of which was shown in FIG. 2, was prepared. Nafion (manufactured by DuPont) was used for an electrolyte membrane. A cathode catalyst layer 22 was formed by applying catalyst slurry on Nafion directly with a spray coater. The cathode catalyst layer 22 was applied on Nafion in the following order.
Firstly, Nafion was put on a hotplate as a substrate, and was fixed by suction. The temperature of the hot plate was 50° C. Next, a mask was put on it, and cathode catalyst slurry was sprayed with a spray coater (manufactured by Nordson). The mixture of the catalyst prepared in the example and water, 5% (wt) Nafion solution and 221 solution (the solution of 1-propanol:2-propanol:water=2:2:1) was used in the weight ratio of 2:1.2:5.4:10.6. Spraying condition was 0.01 MPa of hydraulic pressure, 0.15 MPa of swirl pressure, 0.15 MPa of atomization pressure, 60 mm of gun/substrate distance and 50° C. of substrate temperature. The amount of the cathode catalyst was 0.4 mg Pt·cm⁻².
A cathode catalyst layer 22 was formed on a Nafion surface, followed by forming an anode catalyst layer 23 on the opposite surface. The anode catalyst layer 23 was formed by transferal. Firstly, anode catalyst slurry was prepared. A mixture of platinum black HiSPEC1000 (manufactured by Johnson Matthey), 5% (wt) Nafion solution and 221 solution was used in the weight ratio of 1:1.11:2.22. It was applied on Teflon (registered trademark) sheet by an applicator. The anode catalyst layer which was applied on Teflon (registered trademark) sheet was formed on the Nafion surface with heat transfer printing by hot press (SA-401-M manufactured by Tester Sangyo). The pressure of hot press was 37.2 kgf·cm², the temperature of hot press was 120° C., and hot press time was two minutes. The amount of anode catalyst was 4.8 mg Pt·cm⁻².
The prepared MEA was incorporated into the device of manufacturing organic hydride in FIG. 1. Toluene was used as an unsaturated hydrocarbon. In the state that toluene was supplied to cathode in 10 cc/min and purified water was supplied to the anode in 5 cc/min, voltage was applied between the anode and the cathode. It was conducted at 80° C. of the cell temperature. The value of the current to the applied voltage is shown in FIG. 4. When applying 1.6 V or above of voltage, a current flowed and the reaction proceeded. As the voltage was increased to 2.2 V, the current increased and the reaction proceeded. When the cathode emission gas was analyzed by gas chromatography, toluene and methylcyclohexane were detected. Hereby, it was confirmed that methylcyclohexane was yielded by hydrogenation of toluene. FIG. 5 shows the conversion ratio of toluene to methylcyclohexane, calculated from the peak intensity of gas chromatography. As the voltage was increased, the conversion ratio was improved, and the maximum value in this condition was 55% when applying 2.2 V.
As mentioned above, according to the example, a membrane electrode assembly and an organic hydride manufacturing device capable of obtaining higher energy efficiency can be provided by introducing functional groups, which decrease wettability of unsaturated hydrocarbons, on the carrier surface of a catalyst even if organic hydride is manufactured with a single device in one step.

First Comparative Example

As a catalyst, a catalyst was used where 30% (wt) of Pt particulates was dispersed and supported on carbon black for which surface treatment to introduce functional groups was not conducted. This catalyst was used as cathode catalyst to prepare MEA. The preparation was conducted in the method and condition for the preparation similar to those of First Example.
The prepared MEA was incorporated into the device of manufacturing organic hydride in FIG. 1, and the experiment of hydrogenation of toluene in similar condition to First Example was conducted. FIG. 6 shows a value of the current to the applied voltage. The value of the current was smaller than that of First Example. This is considered to be because the wettability of toluene to carbon was strong, toluene was stagnated on the carbon surface, and the supply of toluene onto catalyst was prevented. Furthermore, when the occurred gas flow rate was measured, the gas flow rate was increased in First Comparative Example in comparison with First Example. This is considered to be because, on the catalyst where toluene is not supplied, hydrogen generation occurs by the reaction according to the following formula (3)
2H⁺+2e ⁻→H₂ (3)
FIG. 7 shows the conversion ratio of toluene to methylcyclohexane. The maximum value in this condition was 30% when applying 2.2 V. It was a lower conversion ratio than that of First Example. This is considered to be because not only hydrogenation but also hydrogen generation occurs simultaneously. The energy efficiency of organic hydride production can be lower to that extent.
As mentioned above, even if there is a similar configuration to First Example except for the introduction of functional groups, a membrane electrode assembly and an organic hydride manufacturing device which have higher energy efficiency cannot be obtained.

Second Embodiment

As a catalyst, a catalyst where 30% (wt) of Pt particulates was dispersed and supported on carbon black was used. 10 g of this catalyst and 15 g of anhydrous aluminum chloride (AlCl₃) were mixed and thiophosphoryl chloride (PSCl₃) was added gradually. The temperature of PSCl₃was fixed at 35° C. and 54 mL was added slowly. Subsequently, it was kept at 75° C. for 45 minutes. After cooling, 50 mL of chloroform was added and filtrated. After washing with diethyl ether thoroughly, 200 mL of ion-exchanged water was added and refluxed for 20 hours. When the infrared absorption spectrum of the obtained catalyst was measured, the peaks were observed at 1000 to 1120 cm⁻¹and 840 to 910 cm⁻¹. This was considered as the peak based on phosphonate, and it was confirmed that phosphonate groups were introduced onto the surface of the carrier carbon black. The equivalent of the introduced phosphonate groups was 1.8 milliequivalent/g dry carbon carrier.
The prepared catalyst was used for cathode catalyst to prepare an MEA. The preparation was conducted in the method and condition for the preparation similar to those of First Example.
The prepared MEA was incorporated into the device of manufacturing organic hydride in FIG. 1, and the experiment of hydrogenation of toluene was conducted in the similar condition to First Example. The result is shown in FIG. 8. FIG. 8 is the current density and the conversion ratio when applying 2.2 V between the anode and the cathode. Compared to First Comparative Example in which surface treatment of carrier carbon was not conducted, it resulted in an increase of both the current density and the conversion ratio, and the effect of introducing phosphonate groups onto the carbon surface was found.
As mentioned above, according to the example, a membrane electrode assembly and an organic hydride manufacturing device capable of obtaining higher energy efficiency can be provided by introducing functional groups, which decrease wettability of unsaturated hydrocarbons, on the carrier surface of catalyst even if organic hydride is manufactured with a single device in one step.

Third Example

As a catalyst, a catalyst where 30 wt % of Pt particulates was dispersed and supported on carbon black was used. Oxygen plasma was irradiated to this catalyst. The device to use for irradiation was a plasma device, Cat. No. PDC210 manufactured by Yamato Glass, and the pressure in the chamber before introducing oxygen was 0.1 Torr or lower, and the pressure after introducing oxygen was 0.5 Torr. The output of a high frequency power source of the device was 100 W, and plasma irradiation time was 150 seconds. When infrared absorption spectrum of the yielded catalyst was measured, a broad peak was observed at 3000 to 3600 cm⁻¹. This was considered as the peak based on the hydroxyl group —OH, and it was confirmed that the hydroxyl group was introduced on the surface of Pt supported carbon black.
The prepared catalyst was used for cathode catalyst to prepare an MEA. The preparation was conducted in the method and condition for the preparation similar to those of First Example.
The prepared MEA was incorporated into the device of manufacturing organic hydride in FIG. 1, and the experiment of hydrogenation of toluene in the similar condition to First Example. The result is shown in FIG. 8. Compared to First Comparative Example in which surface treatment of carrier carbon was not conducted, it resulted in an increase of both the current density and the conversion ratio, and the effect of introducing hydroxyl groups onto the carbon surface was found.
As mentioned above, according to the example, a membrane electrode assembly and an organic hydride manufacturing device capable of obtaining higher energy efficiency can be provided by introducing functional groups, which decrease wettability of unsaturated hydrocarbons, on the carrier surface of catalyst even if organic hydride is manufactured with a single device in one step.
However, the present invention is not limited the above-mentioned examples, and various modifications are included. For example, the above-mentioned examples are explained in detail to explain the present invention simply, and not necessarily limited to that provides all the configurations explained. In addition, it is also possible to substitute part of the configuration of one example with configuration of another example, and moreover, it is also possible to add, to the configuration of one example, the configuration of another example. Furthermore, for part of the configuration of each example, it is possible to make addition, deletion, or substitution of another configuration.

Claims

What is claimed is:

1. A membrane electrode assembly in which a cathode catalyst layer which reduces an unsaturated hydrocarbon and an anode catalyst layer which oxides water are placed to sandwich a solid polymer electrolyte membrane which is proton conductive,

wherein the cathode catalyst layer includes a catalytic metal which causes hydrogenation of a unsaturated hydrocarbon to organic hydride, a carrier which supports the catalytic metal, and the solid polymer electrolyte membrane which is proton conductive; and

a functional group which decreases wettability of the unsaturated hydrocarbons is introduced onto a surface of the carrier.

2. An organic hydride manufacturing device, comprising the membrane electrode assembly according to claim 1, a member supplying the unsaturated hydrocarbon to the cathode catalyst layer, and a member supplying water or steam to the anode catalyst layer.

3. The membrane electrode assembly according to claim 1, wherein the functional group includes at least one of a sulfonate group, a phosphonate group, a hydroxyl group, a sulfomethyl group, a carboxyl group, a carbonyl group, and a carboxylate group.

4. The membrane electrode assembly according to claim 1, wherein the catalytic metal consists of platinum, ruthenium, rhodium, palladium, iridium, molybdenum, rhenium, wolfram, and an alloy including at least some of these.

5. The membrane electrode assembly according to claim 1, wherein the unsaturated hydrocarbon is benzene, toluene, xylene, mesitylene, naphthalene, methylnaphthalene, or anthracene.

6. The organic hydride manufacturing device according to claim 2, wherein the unsaturated hydrocarbon is benzene, toluene, xylene, mesitylene, naphthalene, methylnaphthalene, or anthracene.

7. An organic hydride manufacturing device comprising a cathode catalyst layer, an anode catalyst layer, and a separator which supplies an unsaturated hydrocarbon to the cathode catalyst layer to remove organic hydride, and supplies H₂O to the anode catalyst layer to evacuate oxygen and water,

wherein the cathode catalyst layer is placed on one surface of a solid polymer electrolyte membrane, and the anode catalyst layer is placed on another surface of the solid polymer electrolyte membrane,

the cathode catalyst layer includes a catalytic metal which causes hydrogenation of an unsaturated hydrocarbon to the organic hydride, and a carrier which supports the catalytic metal, and

the carrier has on its surface a functional group which decreases wettability of the unsaturated hydrocarbon.

8. The organic hydride manufacturing device according to claim 7, wherein hydrogen is supplied from the anode catalyst layer to the cathode catalyst layer.

9. The organic hydride manufacturing device according to claim 7, wherein the carrier is electron-conductive carbon.

10. The organic hydride manufacturing device according to claim 7, wherein the functional group is a sulfonate group.

11. The organic hydride manufacturing device according to claim 7, wherein the separator has electroconductivity as well as a channel groove through which unsaturated hydrocarbons and H₂O flow.

12. The organic hydride manufacturing device according to claim 7, wherein supply of unsaturated hydrocarbons onto the cathode catalyst layer and supply of H₂O onto the anode catalyst layer are feasible via a diffusion layer.

13. The organic hydride manufacturing device according to claim 12, wherein the diffusion layer is carbon paper or carbon cloth.

14. The organic hydride manufacturing device according to claim 7, wherein the cathode catalyst layer includes a solid polymer electrolyte.