JP4090108B2 - Membrane / electrode assembly for polymer electrolyte fuel cells - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polymer electrolyte fuel cell, and more particularly to a membrane / electrode assembly.
[0002]
[Prior art]
The fuel cell is one that converts the chemical energy of the fuel directly into electrical energy by electrochemically oxidizing hydrogen, methanol, or the like in the cell, and has attracted attention as a clean electrical energy supply source. In particular, the polymer electrolyte fuel cell is expected to be an alternative power source for automobiles because it operates at a lower temperature than others.
In such a polymer electrolyte fuel cell, a pair of gas diffusion electrodes are joined to both surfaces of a polymer electrolyte membrane. That is, an anode catalyst layer is provided on one side of the solid polymer electrolyte membrane, a cathode catalyst layer is provided on the other side, and a pair of gas diffusion layers are adjacent to each other on both sides. . Conventionally, the anode and cathode catalyst layers are formed by sheeting a mixture of carbon black powder supporting an electrode catalyst, a polymer having proton conductivity, and a polymer having water repellency. Are joined by hot pressing.
[0003]
Fuel (for example, hydrogen) is supplied to the gas diffusion electrode side as the anode, and an oxidant (for example, oxygen or air gas) is supplied to the gas diffusion electrode side as the cathode, and the two electrodes are connected by an external circuit. Operates as a battery. That is, in the anode, protons and electrons are generated by the oxidation of the fuel, and these protons pass through the solid electrolyte and move to the cathode side. On the other hand, electrons reach the cathode through an external circuit. At the cathode, water is generated by such protons and electrons and oxygen in the oxidizing agent, and at this time, electric energy can be taken out.
[0004]
[Problems to be solved by the invention]
In order for protons to move smoothly in the solid polymer electrolyte membrane, water is required, so the fuel is humidified and supplied to the anode together with water. Excess water generated at the cathode and moving through the membrane is released outside the electrode together with the oxidizing agent. In the catalyst layer, in order to obtain a high catalyst utilization rate, as described in JP-A-6-333574, for example, a commercially available “Nafion (5 wt% solution)” manufactured by Aldrich, USA A proton conductive polymer having a high water content is uniformly dispersed. Therefore, even when a water-repellent polymer is included, it is difficult for water to be smoothly discharged from the catalyst layer to the outside of the layer or the gas diffusion layer. While the fuel cell continues to operate, water gradually accumulates in the catalyst layer and gas diffusion layer, and the higher the current density, the more water accumulates and the oxidant is supplied to the catalyst layer. Is greatly disturbed. As a result, the resistance of the electrochemical reaction becomes extremely large, causing a problem that the battery voltage that can be taken out is greatly reduced, and that voltage variation between cells is increased in the stack.
[0005]
By operating the fuel and oxidant under pressure and increasing the fuel cell operating pressure, the reaction efficiency of the electrode increases, but the discharge capacity of produced water and the like decreases conversely due to a decrease in gas flow rate. Improvement in characteristics cannot be expected.
Increasing the amount of the water-repellent polymer dispersed in the catalyst layer is constrained to cause a significant decrease in the catalyst utilization rate and a decrease in output voltage, and a significant improvement in water repellency cannot be expected. In addition, since a proton conductive polymer is contained, a high temperature treatment as described in, for example, Japanese Patent Publication No. 5-20868 is performed after a water repellent polymer such as PTFE is dispersed in the catalyst layer. Cannot be used to form an effective matrix of water repellent polymer.
[0006]
Further, the battery characteristics at high current density can be improved without humidifying the oxidizing agent or by a method of humidifying at a lower temperature than the cell temperature. However, on the contrary, in the low current density region, the film or the like is dried, and the battery voltage is greatly reduced.
The present invention has been made paying attention to such a problem of the prior art, and improves the water discharging ability in the catalyst layer while preventing the membrane from being dried, so that water for diffusion of the reaction gas into the catalyst layer can be improved. The object of the present invention is to provide a membrane / electrode assembly for a polymer electrolyte fuel cell that exhibits a stable high battery voltage from a low current density to a high current density region.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, in a membrane / electrode assembly for a polymer electrolyte fuel cell in which catalyst layers containing at least electrode catalyst particles and a proton conducting polymer are present on both sides of the polymer electrolyte membrane, Provided is a membrane / electrode assembly comprising an EW proton conducting polymer layer different from a solid polymer membrane at an interface where the solid polymer membrane and at least one catalyst layer are in contact with each other. By producing such a membrane-electrode assembly, it has been found that a stable battery voltage can be obtained from a low current density to a high current density region, and the present invention has been achieved.
That is, the present invention
1. In a membrane / electrode assembly for a polymer electrolyte fuel cell in which a catalyst layer containing at least electrocatalyst particles and a proton conducting polymer exists on both sides of the polymer electrolyte membrane, at the interface where the cathode catalyst layer and the polymer electrolyte membrane are in contact with each other Only EW than solid polymer membrane Is high and Thickness 0.1 ~ 10μm It is a three-dimensional layer that partially penetrates the surface of the catalyst layer and the inside thereof. A membrane-electrode assembly having a proton conductive polymer layer,
2. In a membrane / electrode assembly for a polymer electrolyte fuel cell in which a catalyst layer containing at least electrocatalyst particles and a proton conducting polymer exists on both sides of the polymer electrolyte membrane, at the interface where the cathode catalyst layer and the polymer electrolyte membrane are in contact with each other EW than solid polymer membrane Is high and Thickness 0.1 ~ 10μm It is a three-dimensional layer that partially penetrates the surface of the catalyst layer and the inside thereof. It has a proton conductive polymer layer and has an EW higher than the solid polymer membrane at the interface where the anode catalyst layer and the solid polymer membrane are in contact. Is high and Thickness 0.1 ~ 10μm It is a three-dimensional layer that partially penetrates the surface of the catalyst layer and the inside thereof. A membrane-electrode assembly having a proton conductive polymer layer,
3. In a membrane / electrode assembly for a polymer electrolyte fuel cell in which a catalyst layer containing at least electrocatalyst particles and a proton conducting polymer exists on both sides of the polymer electrolyte membrane, at the interface where the cathode catalyst layer and the polymer electrolyte membrane are in contact with each other EW than solid polymer membrane Is high and Thickness 0.1 ~ 10μm It is a three-dimensional layer that partially penetrates the surface of the catalyst layer and the inside thereof. It has a proton-conducting polymer layer, and is closer to the interface where the anode catalyst layer and solid polymer membrane are in contact than the solid polymer membrane. EW is low, and Thickness 0.1 ~ 10μm It is a three-dimensional layer that partially penetrates the surface of the catalyst layer and the inside thereof. A membrane-electrode assembly having a proton conductive polymer layer.
[0008]
The operation of dispersing the proton conductive polymer in the catalyst layer is intended to greatly improve the utilization rate of the catalyst, but in order to exert its effect more, a polymer having a high proton conductivity, i.e. It is desirable to use a polymer with a lower EW. As the proton conductive polymer, perfluorosulfonic acid polymers represented by the above-mentioned Nafion are widely used. For example, in this perfluorosulfonic acid polymer, a polymer having a lower proton conductivity and a higher proton conductivity exhibits a relatively high hydrophilicity and has a high water content. In the battery reaction, protons oxidized on the anode catalyst reach the membrane through the polymer having high proton conductivity, move through the membrane having the same conductivity to the cathode side, and again, It reaches the cathode catalyst through the highly proton conducting polymer dispersed in the catalyst layer. Using this as a three-phase interface, it reacts again with oxygen gas as an oxidant reaction gas and electrons that have passed through an external circuit to produce water. Furthermore, proton-accompanied water due to gas humidification moves to the cathode, and more water is generated in the cathode catalyst layer along with the operating current density.
[0009]
In addition, as a preferred embodiment of the proton conductive polymer layer of EW different from the solid polymer film, which is formed at the interface where the solid polymer film and at least one catalyst layer are in contact with each other, the solid polymer film and the cathode are used. A proton conductive polymer layer having a higher EW than the solid polymer membrane is formed only at the interface where the catalyst layer is in contact, or at the interface and the interface where the solid polymer membrane is in contact with the anode catalyst layer. The proton conductive polymer layer is preferably a substantially three-dimensional layer partially penetrating into the surface of the catalyst layer formed by a casting method described later and the inside thereof. By forming this layer, the proton-accompanying water is effectively prevented from moving to the cathode and water accumulation in the cathode catalyst layer is suppressed. Further, during operation at a low current density, it functions as a barrier that prevents the membrane from drying, and has a role of maintaining the water retention of the membrane. Thus, the water produced at the cathode is quickly discharged out of the gas diffusion layer and the electrode from above the catalyst active point, through the holes serving as passages in the catalyst layer. Thus, at the cell reaction catalyst active point, an electrode having a high product water discharge capability can be obtained while maintaining a high reaction rate.
[0010]
Here, EW mentioned above represents the equivalent weight of the exchange group having proton conductivity. The equivalent weight is the dry weight of the ion exchange membrane per equivalent of ion exchange group, and is expressed in units of “g / ew”.
Further, as a more preferable embodiment of the proton conductive polymer layer, a proton conductive polymer layer having a higher EW than the solid polymer membrane is formed on the cathode side, and a lower EW than the solid polymer membrane is formed on the anode side. A proton conducting polymer layer is formed. This makes it possible to use the difference in hydrophilicity or hydrophobicity to retain the water in the membrane even when the fuel or oxidizer is insufficiently humidified, when the operating current density of the battery is low, or even when the operation is stopped. It is possible to maintain high proton conductivity. In this way, by setting the EW of the proton conducting polymer layers on both sides of the cathode and anode to be higher or lower than that of the solid polymer membrane, mass transfer of proton-entrained water and cathode generated water in the membrane can be made according to operating conditions. Can be designed widely. Furthermore, a combination with EW of the proton conductive polymer of the catalyst layer is also possible.
[0011]
The thickness of the proton conductive polymer layer is 0.05 to 20 μm, more preferably 0.1 to 10 μm. When the thickness is 0.05 μm or less, the above-described sufficient function effect cannot be obtained. On the other hand, when the thickness is 20 μm or more, the resistance increases, which is not suitable. The EW of the proton conductive polymer layer may be at least 700 or more, more preferably 800 or more. And it is preferable that it is 1500 or less, and it is more preferable that it is 1300 or less. If it is 700 or less, the hydrophilicity is too high and water cannot move smoothly, and if it is 1500 or more, the proton conductivity is too low, the effect of the present invention cannot be shown. The difference in EW between the proton conductive polymer layer and the solid polymer membrane at the interface is preferably 20 or more, more preferably 50 or more, and particularly preferably 100 or more. . In addition, when the difference in EW between the closest numerical values in the case of including three or more kinds of proton conductive polymers is 20 or more, the effect of the present invention can be enjoyed. The upper limit of the EW difference is preferably 800 or less, more preferably 600 or less, and particularly preferably 400 or less.
[0012]
The proton conductive polymer layer may be formed by any forming means, but is preferably produced by a casting method. The casting method here refers to various generally known methods-spraying method, screen printing method, coating method using a bar coater or doctor blade, and a polymer-containing liquid composition such as a brush coating method and curing. Means for forming a film.
The proton conductive polymer may be any polymer that conducts protons, and preferably has at least one of a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, and a phosphoric acid group with a fluorine-containing polymer as a skeleton. Is. In addition, those having a hydrocarbon skeleton such as polyolefin can also be used.
[0013]
Examples of the fluorine-containing polymer include tetrafluoroethylene, trifluoromonochloroethylene, trifluoroethylene, vinylidene fluoride, 1,1-difluoro-2,2-dichloroethylene, 1,1-difluoro-2-chloroethylene, hexa A first group of monomers such as fluoropropylene, 1,1,1,3,3-pentafluoropropylene, octafluoroisobutylene, ethylene, vinyl chloride, and alkyl vinyl ester, and the following general formula (1),
Y- (CF ₂ ) _a -(CFR _f ) _b -(CFR ' _f ) _c -O-
-[CF (CF ₂ X) -CF ₂ -O] _n -CF = CF ₂ (1)
(Where Y is -SO ₂ F, -SO _Three NH, -COOH, -CN, -COF, -COOR (R is an alkyl group having 1 to 10 carbon atoms), -PO _Three H ₂ , -PO _Three H, a is an integer of 0-6, b is an integer of 0-6, c is 0 or 1, provided that a + b + c cannot be equal to 0. X is Cl, Br, F or a mixture thereof when n> 1, and n is 0-6. R _f And R ' _f Are independently selected from the group consisting of F, Cl, a perfluoroalkyl group having about 1-10 carbon atoms and a fluorochloroalkyl group having 1-10 carbon atoms. ), A copolymer of 2 or 3 or more monomers essential for the second group monomer, one or more polymers of the second group, etc. . In particular, a perfluorocarbon polymer having a sulfonic acid group is preferable.
[0014]
Although the polymer should just couple | bond two or more molecules of monomers, the molecular weight is preferable 5000 or more from a durable viewpoint. Furthermore, EW can be adjusted as appropriate by using a mixture of a polymer and a low molecular weight compound.
Proton conducting polymers as described above include, for example, alcohols such as methanol, ethanol, propanol and butanol, N, N′-dimethylacetamide, N, N′-dimethylformamide, dimethyl sulfoxide, sulfolane and the like. It can be used by dissolving it in a polar solvent, a cyclic ether such as tetrahydrofuran, or a mixture of two or more selected from the above solvent group, and a mixture of the above solvent group and water. In particular, a lower alcohol such as ethanol, 1-propanol, or 2-propanol alone or a mixture of two or more solvents and water is preferable. Furthermore, a mixed solvent of at least one of the above solvent groups and a fluorine-containing compound such as a fluorocarbon or a fluorine-containing alcohol can also be used.
[0015]
The concentration of the dissolved proton conductive polymer solution is in the range of 3 to 20% by weight, when an appropriate proton conductive polymer coating is easily formed on the catalyst surface when dispersed in and on the catalyst layer of the gas diffusion electrode. Is preferred. If this concentration is too high, the dispersibility of the polymer in the catalyst layer and on the surface will deteriorate, and the thickness of the coating will become too large, resulting in a non-uniform three-phase interface and a decrease in catalyst utilization. The effect may not be exhibited. On the other hand, if the concentration is too low, a uniform and sufficient thickness of the proton conductive polymer coating on the catalyst surface cannot be obtained, or the proton conductive polymer solution is applied to the surface of the porous catalyst layer sheet to In the case of dispersing in the polymer, the viscosity of the liquid is too low, and therefore the polymer is concentrated locally, which is not preferable.
The electrode catalyst material used for the anode and cathode catalyst layers may be any material that has a catalytic action on the oxidation reaction of hydrogen and the reduction reaction of oxygen, such as platinum, ruthenium, iridium, rhodium, palladium, osnium, tungsten, lead, It can be selected from metals such as iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, or alloys thereof.
[0016]
The particle size of the catalyst is preferably 10 to 300 mm, and more preferably 15 to 100 mm. If it is less than 10 mm, it is practically difficult to manufacture, and if it is more than 300 mm, the catalyst utilization rate decreases, and a high battery voltage cannot be obtained. These catalyst particles may be supported on a conductive material such as carbon black. The amount of catalyst supported is 0.01 to 5 mg / cm with the catalyst layer sheet formed. ² And more preferably 0.1-1 mg / cm ² It is. 0.01mg / cm ² Less than 5 mg / cm, the catalyst performance cannot be exhibited effectively. ² In the above, the cost becomes very large, and the effect corresponding to the amount cannot be seen in terms of performance.
[0017]
The catalyst layer referred to in the present invention is composed of a conductive material such as the catalyst material, proton conductive polymer, and carbon black, and includes a water repellent material such as PTFE and a binder as necessary. May be. As a method for dispersing the proton conductive polymer in the catalyst layer, the catalyst layer constituent materials may be mixed and molded to form a catalyst layer, or other constituent materials other than the proton conductive polymer may be mixed and molded in advance to form a catalyst layer. Then, a proton conductive polymer may be impregnated.
The conductive material may be any electron conductive material. For example, carbon black such as furnace black, channel black, and acetylene black listed above as the carbon material, activated carbon, graphite, and various metals can be applied. .
Proton conductive polymers such as perfluorosulfonic acid also have a function as a binder in the polymer itself, and form a sufficiently stable matrix with catalyst particles and conductive particles in the catalyst layer. Is possible. For the purpose of imparting water repellency in addition to the function as a binder, for example, various resins containing fluorine can also be used. The fluororesin preferably has a melting point of 400 ° C. or lower, and examples thereof include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and the like.
[0018]
In the present invention, the same material as the proton conductive polymer can be used for the membrane used as the solid polymer electrolyte. In other words, those having at least one of a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, and a phosphoric acid group with a fluorine-containing polymer as a skeleton are preferable. A film in which a monomer having a sulfonic acid group or a carboxylic acid group is introduced into a polyolefin film such as polyethylene by a graft polymerization reaction can also be used. The fluorine-containing film is, for example, a copolymer of 2 or more, usually 2 to 3, which is selected from the first group of monomers and the second group of monomers and essentially requires the second group of monomers. In addition to the method of reinforcing the mechanical strength by laminating with a film having a higher EW, these membranes may be reinforced with a perfluorocarbon polymer in a fibril shape, a woven fabric shape, a nonwoven fabric shape, or a porous sheet, The membrane surface can be reinforced by coating with an inorganic oxide or metal.
The EW of these films may be 700 or more, more preferably 800 or more. And it is preferable that it is 1500 or less, and it is more preferable that it is 1300 or less. If it is less than 700, the proton conductivity is improved, but the mechanical strength of the membrane is lowered, which is not practical. Above 1500, the mechanical strength is further improved, but the proton conductivity is increased and the battery voltage is lowered.
[0019]
The catalyst layer can be produced by various generally known methods-spraying method, transfer method, screen printing method, rolling method and the like. After sufficiently stirring a catalyst dispersion liquid composed of a proton conductive polymer, a catalyst, a conductive material, and / or a water-repellent polymer dissolved in a solvent mainly composed of a lower alcohol such as ethanol, for example, in the transfer method, PTFE A catalyst layer is formed on such a smooth sheet by applying and drying the catalyst dispersion to a certain area. At this time, at least two or more types of proton conductive polymers can be added to the catalyst dispersion sequentially or simultaneously in advance to form a catalyst layer in which the proton conductive polymers are uniformly dispersed. As another form, a catalyst layer in which a plurality of catalyst layers in which one or more different proton conductive polymers are dispersed is laminated can be formed by repeatedly forming the catalyst layers. Further, the present invention can take various forms such as a method of directly applying the catalyst dispersion liquid to the membrane, or a combination thereof, and is not limited to the above range.
The EW of the proton conductive polymer of the catalyst layer may be at least 700 or more, more preferably 800 or more. And it is preferable that it is 1500 or less, and it is more preferable that it is 1300 or less. If it is 700 or less, the hydrophilicity is too high and water cannot move smoothly, and if it is 1500 or more, the proton conductivity is too low, the effect of the present invention cannot be shown.
[0020]
By using at least two types of proton conductive polymers in the catalyst layer on the same side of the membrane, the function is shared between the proton conductive polymer that forms the three-phase interface of the catalyst layer and the proton conductive polymer that has a water discharge function. You can also make it. At this time, the difference in EW between the nearest numerical values of the proton conductive polymers is 20 or more, the effect of the present invention can be enjoyed, and 50 or more is more preferable. The upper limit of the EW difference is preferably 800 or less, more preferably 600 or less, and particularly preferably 400 or less.
[0021]
The amount of the proton conductive polymer dispersed in the catalyst layer is in the range of 0.1 to 10 by weight with respect to the amount of catalyst supported. When the weight ratio to the catalyst is 0.1 or less, a sufficient catalyst utilization rate cannot be obtained due to a decrease in the reaction active point. On the other hand, if the weight ratio is 10 or more, the influence of hydrophilicity due to the proton conductive polymer increases, and the effect of the present invention cannot be obtained.
Next, the catalyst layer surface of the sheet on which the catalyst layer is formed is superimposed on both surfaces of the solid polymer electrolyte membrane, and the catalyst layer is bonded to the solid polymer electrolyte membrane under heating and heating. The pressure and temperature at the time of joining are selected from the conditions under which the solid polymer electrolyte membrane, the proton conductive polymer, the catalyst, and the conductive material add sufficient adhesion to each other. In particular, when a perfluorosulfonic acid polymer is used as the solid polymer electrolyte membrane, it may be at least the glass transition point, and the preferred joining temperature is 120 to 200 ° C.
Proton conducting polymer can not obtain sufficient conductivity unless it is finally proton type, but in order to improve the heat resistance of solid polymer membrane and proton conducting polymer at the time of bonding, sodium or potassium It is also effective to substitute a monovalent metal ion or the like, or a divalent or trivalent metal, heat treatment, and finally form a proton type.
[0022]
After the catalyst layer is bonded to the solid polymer membrane, the fuel is further used as a membrane / electrode assembly by bonding or overlapping with an electrically conductive porous woven fabric / nonwoven fabric such as carbon paper or carbon cloth as a catalyst layer support. Can be incorporated into battery cells. Carbon paper and carbon cloth can impart water repellency as needed by impregnating with a polytetrafluoroethylene resin, like the gas diffusion layer. If the porosity of the electrically conductive porous woven fabric or nonwoven fabric is 50% or more, it has a sufficient material exchange function.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not restrict | limited to an Example.
【Example】
Example 1
40 wt% platinum catalyst-supported carbon (manufactured by E-TEK, USA), 5 wt% solution of proton type perfluorosulfonic acid polymer resin (Asahi Kasei Kogyo Co., Ltd., EW = 910, solvent composition: ethanol / water = 50/50) was added so that the weight ratio of the platinum catalyst to the polymer was 2 to 1, and dispersed uniformly to prepare a paste. This paste was applied onto a polytetrafluoroethylene sheet using a 200-mesh screen, and then dried and fixed at 100 ° C. in an air atmosphere to obtain a platinum loading of 0.2 mg / cm 2. ² The catalyst sheet was obtained.
On this fixed catalyst sheet, only a 5% by weight solution of proton type perfluorosulfonic acid polymer resin (same as above) with EW = 1030 was applied using the same screen, dried at 100 ° C. in an air atmosphere, The thickness is about 1 μm, 0.20 mg / cm ² The polymer layer was formed. In this way, a cathode catalyst layer was produced.
[0024]
On the other hand, on the catalyst sheet produced by the same procedure as described above, only a 5 wt% solution of proton type perfluorosulfonic acid polymer resin with EW = 910 (same as above) was applied using the same screen, and was 100 ° C. in the atmosphere. After drying at 0.20 mg / cm, which is about 1 μm in thickness ² The polymer layer was formed. Thus, an anode catalyst layer was produced.
These cathode and anode catalyst layer sheets face each other, and a perfluorosulfonic acid membrane (made by Asahi Kasei Kogyo Co., Ltd.) having an EW = 950 and a thickness of 100 μm is sandwiched between them, 150 ° C., pressure 50 kg / cm. ² After hot pressing, the polytetrafluoroethylene sheets on both sides were peeled off to produce a membrane / electrode assembly.
[0025]
As a catalyst layer support, a carbon cloth having a thickness of about 400 μm (manufactured by E-TEK) was immersed in a tetrafluoroethylene dispersion (60% by weight) and sintered at 340 ° C. 40% by weight impregnation was performed. The porosity was 50%.
These membrane / electrode assembly and catalyst layer support were incorporated into a fuel cell single cell evaluation device, and hydrogen gas was used as the fuel and air gas was used as the oxidant, and a single cell characteristic test was conducted at normal pressure and cell temperature of 70 ° C. . Hydrogen gas was humidified at 80 ° C., and air gas was supplied to the cell as it was without humidification. 0.5, 1.0 A / cm ² When the current density was 0.65 V and 0.50 V, respectively. The following examples and comparative examples were also tested using the same membrane / electrode joining method, catalyst layer support, and single cell operating conditions.
A schematic diagram of the cell structure of Example 1 is shown in FIG.
[0026]
(Example 2)
A membrane / electrode assembly was produced in accordance with Example 1 except that the EW of the perfluorosulfonic acid polymer applied in the cathode catalyst and on the catalyst sheet in Example 1 was 1030.
As single cell battery characteristics, 0.5, 1.0 A / cm ² When the current density was 0.63 V and 0.48 V, respectively.
(Example 3)
On the catalyst layer sheet of Example 1, only a 5% by weight solution of proton type perfluorosulfonic acid polymer resin with EW = 1030 (same as above) was applied using the same screen, and dried at 100 ° C. in an air atmosphere. 0.20 mg / cm with a thickness of about 1 μm ² The polymer layer was formed. This was used as a cathode catalyst layer and an anode catalyst layer.
As single cell battery characteristics, 0.5, 1.0 A / cm ² When the current density was 0.63 V and 0.49 V, respectively.
Example 4
The same cathode catalyst layer as in Example 3 was used. Moreover, this was made into the anode catalyst layer, without providing any proton type perfluorosulfonic acid polymer resin layer on the catalyst layer sheet of Example 1.
As single cell battery characteristics, as single cell battery characteristics, 0.5, 1.0 A / cm ² When the current density was 0.64 V and 0.49 V, respectively.
[0027]
(Comparative Example 1)
In Example 1, a membrane-electrode assembly was prepared by bonding to a membrane without forming any proton type perfluorosulfonic acid polymer resin layer on the cathode catalyst sheet and the anode catalyst sheet. Evaluation was carried out under the same single cell operating conditions as in Example 1. 0.5, 1.0 A / cm ² When the current density was 0.53 V and 0.22 V, respectively.
(Comparative Example 2)
40 wt% platinum catalyst-supported carbon (manufactured by E-TEK, USA), 5 wt% solution of proton type perfluorosulfonic acid polymer resin (Asahi Kasei Kogyo Co., Ltd., EW = 910, solvent composition: ethanol / water = 50/50) was added so that the weight ratio of the platinum catalyst to the polymer was 2 to 1, and dispersed uniformly to prepare a paste. This paste was applied onto a polytetrafluoroethylene sheet using a 200-mesh screen, and then dried and fixed at 100 ° C. in an air atmosphere to obtain a platinum loading of 0.2 mg / cm 2. ² The catalyst sheet was obtained. As the proton conductive polymer layer provided on the anode catalyst sheet and the cathode catalyst sheet, a perfluorosulfonic acid membrane (manufactured by Asahi Kasei Kogyo Co., Ltd.) with EW = 1030 and film thickness of 40 μm was used (anode, cathode catalyst sheet and proton conduction). Bonding with the conductive polymer film was performed at the same time of the next hot pressing.) This was used as an anode catalyst layer and a cathode catalyst layer.
[0028]
These catalyst layers are face to face, and a perfluorosulfonic acid membrane (made by Asahi Kasei Kogyo Co., Ltd.) with EW = 950 and a thickness of 100 μm is sandwiched between them, 150 ° C., pressure 50 kg / cm. ² After hot pressing, the polytetrafluoroethylene sheets on both sides were peeled off to produce a membrane / electrode assembly.
As a gas diffusion layer, a carbon cloth having a thickness of about 400 μm (manufactured by E-TEK) was used and immersed in a tetrafluoroethylene dispersion (60% by weight), and then sintered at 340 ° C. Impregnation by weight%. The porosity was 50%.
These membrane / electrode assembly and gas diffusion layer were evaluated under the same single cell operating conditions as in Example 1. 0.5, 1.0 A / cm ² When the current density was 0.53 V and 0.30 V, respectively.
[0029]
【The invention's effect】
As described above, by forming a layer of proton conductive polymer of EW different from the solid polymer membrane at the interface where the solid polymer membrane and at least one catalyst layer are in contact with each other, water accumulation in the cathode catalyst layer is increased. In addition to having an inhibitory effect, it also functions as a barrier that prevents the film from drying, and can exhibit stable battery characteristics from low current density to high current density.
[Brief description of the drawings]
FIG. 1 is a schematic view of a cell structure of a polymer electrolyte fuel cell to which a membrane / electrode assembly of the present invention is applied.
[Explanation of symbols]
1 Solid polymer membrane
2 Anode
3 Cathode
4 Membrane / electrode assembly
5 Catalyst layer support
6 Separator
7 Catalyst layer
8 Proton conductive polymer layer

Claims (3)

In a membrane / electrode assembly for a polymer electrolyte fuel cell in which a catalyst layer containing at least electrocatalyst particles and a proton conducting polymer exists on both sides of the polymer electrolyte membrane, at the interface where the cathode catalyst layer and the polymer electrolyte membrane are in contact with each other Only having a EW higher than that of the solid polymer membrane and a thickness of 0.1 to 10 μm , and having a proton conductive polymer layer which is a three-dimensional layer partially infiltrated into the catalyst layer surface and inside thereof. Characteristic membrane / electrode assembly. In a membrane / electrode assembly for a polymer electrolyte fuel cell in which a catalyst layer containing at least electrocatalyst particles and a proton conducting polymer exists on both sides of the polymer electrolyte membrane, at the interface where the cathode catalyst layer and the polymer electrolyte membrane are in contact with each other A proton conductive polymer layer which has a higher EW than the solid polymer membrane and a thickness of 0.1 to 10 μm , and is a three-dimensional layer partially infiltrated into the catalyst layer surface and A three-dimensional layer having an EW higher than that of the solid polymer film and a thickness of 0.1 to 10 μm at the interface where the anode catalyst layer and the solid polymer film are in contact , and partially entering the catalyst layer surface and the inside thereof. A membrane-electrode assembly having a proton conductive polymer layer. In a membrane / electrode assembly for a polymer electrolyte fuel cell in which a catalyst layer containing at least electrocatalyst particles and a proton conducting polymer exists on both sides of the polymer electrolyte membrane, at the interface where the cathode catalyst layer and the polymer electrolyte membrane are in contact with each other A proton conductive polymer layer which has a higher EW than the solid polymer membrane and a thickness of 0.1 to 10 μm , and is a three-dimensional layer partially infiltrated into the catalyst layer surface and A three-dimensional layer having an EW lower than that of the solid polymer film and having a thickness of 0.1 to 10 μm at the interface where the anode catalyst layer and the solid polymer film are in contact , and partially entering the catalyst layer surface and the inside thereof. A membrane-electrode assembly having a proton conductive polymer layer.

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