JP2007103175A - Electrode for polymeric fuel cell and polymeric fuel cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a PEFC and a PEFC using the same showing high output performance and durability over a low temperature state through a high temperature state of humidifying temperature of fuel or an oxidant. <P>SOLUTION: On the electrode for the polymeric fuel cell of which is provided with a catalyst layer containing catalytic powder carrying catalytic metal mainly on a contact face of a proton conducting passage made of cation exchange resin and a surface of carbon, the catalyst layer contains not less than two kinds of catalytic powder of which ion exchanging capacities of the cation exchange resin are different from each other, and respective values of ion exchanging capacities of the cation exchange resin contained in the catalytic powder are not less than 1 milliequivalent/1 gram of dried resin, and less than 1 milliequivalent/1 gram of dried resin. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polymer fuel cell electrode using a cation exchange membrane and a polymer fuel cell using the same.

  A single cell of a polymer fuel cell (PEFC) has a structure in which a membrane / electrode assembly is sandwiched between a pair of gas flow plates. The membrane / electrode assembly is obtained by bonding an anode to one surface of a cation exchange membrane and a cathode to the other surface. A gas flow path is processed in the gas flow plate. For example, power is obtained by supplying hydrogen as fuel to the anode and oxygen as oxidant to the cathode. In the anode and cathode, the following electrochemical reaction proceeds.

Anod: 2H ₂ → 4H ⁺ + 4e ⁻
Cathode: O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O
The electrochemical reaction as described above is performed at an interface where a reactant such as an oxidant or a fuel, protons (H ⁺ ), and electrons (e ⁻ ) exist (hereinafter, this interface is referred to as a reaction interface). proceed.

  The PEFC electrode includes a catalyst layer containing a catalyst metal and a conductive porous body. As the conductive porous body, porous carbon paper, carbon felt, carbon cloth or the like imparted with water repellency is used.

  For example, as disclosed in Patent Document 1, a conventional PEFC electrode is applied to a cation exchange membrane or a conductive porous body with a mixture of a carbon powder supporting a catalyst metal and a solution of a cation exchange resin. The catalyst layer includes a cation exchange resin as a polymer electrolyte, carbon powder, and a catalyst metal.

  As described in Non-Patent Document 1 and Non-Patent Document 2, cation exchange resins such as perfluorosulfonic acid resin are microscopically divided into a hydrophobic region in which main chains are assembled and a hydrophilic region in which side chains are assembled. It is known to have a phase separated structure.

  Since the hydrophobic region is a structure similar to polytetrafluoroethylene, there is significantly less permeation of reactants and water. On the other hand, in the proton conduction path, the ion exchange group bonded to the tip of the side chain forms a cluster, and when water is taken into the cluster, the counter ion becomes movable. That is, water, protons and reactants (hydrogen or oxygen) can move through the proton conduction path.

  Therefore, the catalytic metal supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface can form a reaction interface and is active for electrochemical reaction. Conversely, the catalytic metal present at the contact surface between the hydrophobic region of the cation exchange resin and the carbon surface is inert to the electrochemical reaction because the reactant and proton are not supplied.

  In the PEFC electrode obtained by the conventional manufacturing method, the catalyst metal is present at the contact surface between the hydrophobic region of the cation exchange resin and the carbon surface, that is, other than the reaction interface, and is an inert catalyst metal. Therefore, the utilization rate of the catalyst metal is remarkably low. That is, Non-Patent Document 3 shows that the catalyst utilization rate is about 10%.

  Patent Document 2 discloses a technique for increasing the utilization rate of a catalyst metal in a catalyst layer of a PEFC electrode. That is, the catalyst metal is mainly supported on the reaction interface formed at the contact surface between the proton conduction path of the cation exchange resin and the carbon surface. Non-patent document 4 shows that the utilization rate of the catalyst metal in the catalyst layer is extremely high. Hereinafter, the “electrode on which the catalytic metal is mainly supported on the reaction interface formed at the contact surface between the proton conduction path of the cation exchange resin and the carbon surface” will be referred to as “ultra-small amount catalyst supporting electrode”.

  Techniques using a plurality of catalyst layers in PEFC are disclosed in Patent Document 3, Patent Document 4, and Patent Document 5. In Patent Document 3, the active layer (catalyst layer) is composed of at least two layers, the average equivalent weight of the ionomer in each layer is at least 50 different, and the active layer located closest to the solid polymer electrolyte membrane has an average equivalent weight. A lower equivalent weight ionomer adjacent to the solid polymer electrolyte membrane provides a region with a higher water content for better performance at a lower current density, while more Less hydrophilic high equivalent weight ionomers help to transfer water from the membrane at high current densities.

  In Patent Document 4, in PEFC, the innermost catalyst in contact with the polymer electrolyte membrane is provided with a cathode having a gas diffusion layer and a plurality of catalyst layers arranged between the gas diffusion layer and the polymer electrolyte membrane. Between the ion exchange capacity X (milli equivalent / g dry resin) of the ion exchange resin contained in the layer and the ion exchange capacity Y of the ion exchange resin contained in the outermost catalyst layer in contact with the gas diffusion layer A technique that satisfies the relationship of 0.18 ≦ (X−Y) ≦ 0.70 is disclosed and sufficiently prevents flooding even when a large current flows in the initial stage of startup.

Further, in Patent Document 5, a catalyst layer containing at least two types of ion exchange resins having different catalyst powder and EW (equivalent weight of ion exchange groups) is formed, and the EW of the ion exchange resin in the catalyst layer is defined as the catalyst layer. The EW in the thickness direction of the catalyst layer is changed to be large on the gas diffusion layer side and small on the solid polymer electrolyte membrane side, and an ion exchange resin is placed in the catalyst layer. In the PEFC that is included, it is intended to prevent excessive and insufficient moisture in the electrolyte and gas diffusion inhibition.
Japanese Patent Laid-Open No. 11-045730 JP 2000-01204 A JP 2001-185158 A JP 2001-338654 A JP 2002-164057 A H. L. Yeager et al. Electrochem. Soc. , 128, 1880, (1981) Okumi et al. Electrochem. Soc. , 132, 2601 (1985) Edson A. Ticianelli, J. et al. Electroanal. Chem, 251, 275 (1988) Shuji Hitomi et al., 40th Battery Discussion Meeting, 167-168, (1999)

  In PEFC using an ultra-small amount catalyst-supporting electrode, there is an advantage that the utilization rate of the catalyst metal in the catalyst layer is extremely high. However, in the ultra-small catalyst-carrying electrode, the catalyst metal is mainly carried on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface, so that excess water accumulates in the catalyst layer, thereby The problem is that the output performance is significantly affected by so-called flooding, which is significantly reduced.

  In order to suppress this flooding, by using a cation exchange resin having a small ion exchange capacity, the amount of water taken in by the cation exchange resin is reduced, and the amount of water remaining in the electrode is reduced. Improved output performance.

  However, in the ultra-small catalyst-carrying electrode provided with a cation exchange resin having a small ion exchange capacity value in the catalyst layer, the output performance of the PEFC is remarkably lowered as the humidification temperature of the fuel or oxidant is lowered. It has been clarified that this decrease in output is caused by a reduction in the water content of the cation exchange resin contained in the electrode.

  One cause of this phenomenon is that the water content of the resin is significantly reduced due to its lowering because the resin has less moisture uptake. In addition, the results of research also revealed that the durability performance of PEFC decreases due to the decrease in output performance. In other words, in order to maintain the output performance and durability performance of PEFC, it has been essential to accurately control the humidification temperature of the fuel and the oxidant.

  However, the precise control is very complicated in practical PEFC. That is, in order to improve the output performance and durability performance of PEFC, it has been a problem to maintain the moisture content of the electrode within an appropriate range from a low humidification temperature to a high humidification temperature.

  The techniques disclosed in Patent Documents 3 to 5 differ in the ion exchange capacity or equivalent weight (EW) of the ion exchange resin contained in the catalyst layer in the thickness direction of the catalyst layer. When applied to a conventional method for producing a catalyst layer as described in Document 1, it is difficult to randomly form domains of a catalyst coated with ion exchange resins having different ion exchange capacities. No technology is disclosed.

  The technology to randomly form catalyst domains coated with ion exchange resins with different ion exchange capacities is achieved for the first time by a method for producing ultra-small catalyst-carrying electrodes in which carbon particles and ion exchange resins are integrated in advance. Is possible.

  An object of the present invention is to provide a PEFC electrode that exhibits high output performance and durability performance even from a low to high humidification temperature of a fuel or an oxidizer, and a PEFC using the same.

  The invention of claim 1 is an electrode for a polymer fuel cell comprising a catalyst layer containing a catalyst powder mainly supported on a contact surface between a proton conduction path of a cation exchange resin and a carbon surface. The catalyst layer includes two or more kinds of catalyst powders having different ion exchange capacities of cation exchange resins.

  The invention of claim 2 is such that the ion exchange capacity value of the cation exchange resin contained in the catalyst powder of the polymer fuel cell electrode according to claim 1 is 1 milliequivalent / g dry resin or more and 1 milliequivalent / It is characterized by being less than g dry resin.

  According to a third aspect of the present invention, there is provided a polymer fuel cell comprising the polymer fuel cell electrode according to the first or second aspect.

  In the polymer fuel cell electrode comprising a catalyst powder in which the catalyst metal is mainly supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface, the cation exchange resin has a large ion exchange capacity value and is small. By using two or more kinds of catalyst powders with cation exchange resin, the cation exchange resin dries the electrode excessively, and the cation exchange resin takes in excessive moisture. Electrode flooding can be suppressed.

  As a result, it is possible to improve the output performance and durability performance of the PEFC including the electrode even when the humidification temperature of the fuel and the oxidizer is low to high.

  FIG. 1 shows a schematic view of a catalyst powder in which a catalyst metal contained in an ultra-small catalyst-carrying electrode is carried mainly on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface. In FIG. 1, 11 is carbon particles, 12 is a cation exchange resin, 13 is a proton conduction path (hydrophilic region) of the cation exchange resin, 14 is a hydrophobic region of the cation exchange resin, and 15 is a catalyst metal.

  As shown in FIG. 1, the surfaces of the carbon particles 11 are covered with a cation exchange resin 12. The cation exchange resin 12 includes a proton conduction path (hydrophilic region) 13 and a hydrophobic region 14. A catalytic metal 15 is selectively supported on the contact surface between the proton conduction path 13 and the surface of the carbon 11.

  The proton conduction path (hydrophilic region) 13 serves as a passage for discharging the reaction gas and water. Therefore, since the catalytic metal 15 supported on the contact surface between the proton conduction path 13 of the cation exchange resin 12 and the surface of the carbon 11 can form a reaction interface, it is active against an electrochemical reaction. .

  Since the ultra-small catalyst-carrying electrode has a special structure as shown in FIG. 1, it is strongly affected by flooding due to water retention. From the research results, it became clear that the output performance and durability performance of PEFC equipped with an ultra-small amount of catalyst-carrying electrode deteriorated due to the flooding.

  The present invention relates to a PEFC comprising an electrode by mixing a catalyst powder comprising a cation exchange resin having a large ion exchange capacity value and a catalyst powder comprising a cation exchange resin having a small ion exchange capacity value. This is based on the discovery that the output performance and durability performance of this product are significantly improved.

  As the cation exchange resin, a fluororesin resin such as perfluorosulfonic acid resin is often used because it is chemically stable and has high proton conductivity. The cation exchange resin has a special structure in which a phase separation into a hydrophobic region where fluorocarbon main chains are assembled and a hydrophilic region where side chains having sulfone groups are associated.

  The hydrophilic region of the cation exchange resin has a property of taking water from the outside. This water uptake causes protons to ionize from the sulfone group and move through the hydrophilic region. When the sulfonic acid group is small, in other words, when the ion exchange capacity is small, the hydrophilic region is small and the amount of water taken up is also small. On the contrary, when the ion exchange capacity is large, the hydrophilic region becomes large and the amount of water taken up also increases.

  When a catalyst powder including a cation exchange resin having a small ion exchange capacity is used, electrode flooding is unlikely to occur, but the electrode is easily dried due to a decrease in the humidity of the fuel or oxidant.

The ion exchange capacity of the cation exchange resin can be measured by the following method. After producing a cast membrane using a cation exchange resin solution, a certain amount is cut out and immersed in an aqueous HCl solution, and this solution is replaced several times to make the cation exchange resin a proton type. Next, the cast membrane is placed in distilled water, thoroughly washed until HCl leaching is not observed, and then repeatedly immersed in a 2N NaCl aqueous solution to exchange H ⁺ and Na ^+, and then comes out into the solution. The total amount of H ⁺ is titrated with a standard caustic soda solution. Next, the cast film in the Na ⁺ form is washed with distilled water until Cl ⁺ leaching is not observed, taken out, wiped off excess moisture on the film surface, and then vacuum dried at 170 ° C. After sufficiently removing moisture, the cast membrane is quickly transferred to a sealed container, and the dry weight of the membrane is weighed. The ion exchange capacity is calculated by dividing the equivalent weight (eq) obtained by titration of H ⁺ by the dry weight (g) of the membrane. The reciprocal of the ion exchange capacity is the EW value.

  Hereinafter, a catalyst powder having a cation exchange resin having a large ion exchange capacity value is referred to as a “high capacity catalyst powder”, and a catalyst powder having a cation exchange resin having a small ion exchange capacity value is referred to as a “low capacity catalyst powder”. I will call it.

  FIG. 2 shows a schematic diagram of an ultra-small catalyst supporting electrode provided with a high capacity catalyst powder and a low capacity catalyst powder of the present invention. In FIG. 2, 21 is an ultra-small catalyst supporting electrode, 22 is a catalyst layer, 23 is a conductive porous body, 24 is a high capacity catalyst powder, 25 is a low capacity catalyst powder, and 26 is a cation exchange membrane.

  As shown in FIG. 2, the ultra-small catalyst supporting electrode 21 includes a catalyst layer 22 and a conductive porous body 23, and the catalyst layer 22 includes a high capacity catalyst powder 24 and a low capacity catalyst powder 25. The high capacity catalyst powder 24 and the low capacity catalyst powder 25 are randomly present in the catalyst layer 22. Furthermore, the ultra-small catalyst carrying electrode 21 can be joined to the cation exchange membrane 26 to form a membrane / electrode assembly.

  In the PEFC electrode of the present invention, when the humidification temperature of the PEFC is low, drying of the electrode is suppressed by the high water retention of the high-capacity catalyst powder 24, and when the humidification temperature is high, the low-capacity catalyst powder 25 Since the flooding of the electrode is prevented by the low water retention, it is possible to suppress the drying of the electrode and the occurrence of flooding accompanying the increase and decrease of the humidification temperature.

  Therefore, the output performance of the PEFC including the PEFC electrode of the present invention is stable from a low humidification temperature state to a high state. Furthermore, since the output performance is stabilized, deterioration of the electrode is suppressed, so that the durability performance of the PEFC can be improved.

  In the electrode for PEFC of the present invention, the ion exchange capacity of the cation exchange resin contained in the high capacity catalyst powder is 1 meq / g dry resin or more, and the ion of the cation exchange resin contained in the low capacity catalyst powder. By making the exchange capacity less than 1 milliequivalent / g dry resin, the effect of preventing flooding can be enhanced.

  In the present invention, the ion exchange capacity of the cation exchange resin contained in the high capacity catalyst powder is preferably 1.1 to 1.4 meq / g dry resin, and is contained in the low capacity catalyst powder. The range of the ion exchange capacity of the cation exchange resin is 0.8 meq / g dry resin or more and less than 1.0 meq / g dry resin.

  In the PEFC electrode of the present invention, the cation exchange resin contained in the catalyst powder may have three or more ion exchange capacities. In that case, among the cation exchange resins contained in the catalyst powder, at least one ion exchange capacity is 1 meq / g dry resin or more, and at least one ion exchange capacity is less than 1 meq / g dry resin. It is preferable.

  In the catalyst layer provided with the catalyst powder of the present invention, a high capacity catalyst powder is present in a large amount of sulfur, and conversely, a low capacity catalyst powder is present in a low amount of sulfur. By analyzing the distribution of sulfur in the catalyst layer using electron probe microanalysis (EPMA), the low-capacity catalyst powder and the high-capacity catalyst powder are mixed, and the catalysts are mixed. The mixing ratio of the powder can be examined.

  The procedure for preparing the catalyst powder used in the PEFC electrode of the present invention is as follows. First, a dispersion containing a cation exchange resin solution and carbon is prepared, and then the solvent is removed from the dispersion to produce a mixture containing the cation exchange resin and carbon.

Next, after preparing a solution in which a compound containing a catalyst metal cation is dissolved in water or water containing alcohol, a mixture containing a cation exchange resin and carbon is immersed in the solution, and cation exchange is performed. (for perfluorosulfonic acid resin -SO 3 ^_-) fixed ions of the resin to adsorb the cations containing a catalytic metal, then washed and dried with deionized water.

  Finally, the adsorbed cation is reduced in a hydrogen atmosphere to prepare a fuel cell catalyst in which a catalytic metal is mainly supported on the contact surface between the carbon surface and the proton conduction path of the cation exchange resin. .

  The catalytic metal contained in the catalyst mixture obtained by the production method of the present invention is mainly supported on the contact surface between the carbon surface and the proton conduction path of the cation exchange resin. The contact surface between the carbon surface and the proton conduction path of the cation exchange resin is a place where electrons and protons can be exchanged at the same time, so the catalytic metal supported on this contact surface is efficient for electrode reactions. Involved. Therefore, the usage amount of the catalyst metal can be reduced by increasing the ratio of the catalyst metal supported on the contact surface.

  In the catalyst mixture for PEFC of the present invention, “the catalyst metal is mainly supported on the contact surface between the proton conduction path of the cation exchange resin and the surface of the carbon material” means that the proton conduction path of the cation exchange resin It means that the amount of the catalyst metal supported on the surface of the carbon particles in contact is 50% by mass or more of the total amount of the catalyst metal supported. That is, 50% by mass or more of the total catalytic metal loading is a catalytic metal active for the electrode reaction, so that the utilization rate of the catalytic metal is remarkably increased.

  In the present invention, the ratio of the amount of the catalyst metal supported on the surface of the carbon particles in contact with the proton conduction path of the cation exchange resin to the total amount of the catalyst metal supported is preferably as high as possible, particularly exceeding 80% by mass. preferable. Thus, the electrode can be highly activated by supporting the catalytic metal at a high rate on the contact surface between the proton conduction path and the carbon particles.

  In the catalyst mixture of the present invention, the catalyst metal is mainly supported on the contact surface between the carbonaceous material and the proton conduction path of the cation exchange resin. This can be seen from the mass activity in the high current density region of PEFC equipped with this catalyst mixture and the volume ratio between the proton conduction path of the cation exchange resin and the hydrophobic skeleton (M. Kohmoto et. Al.,). GS Yuasa Technical Report, 1, 48 (2004)). This mass activity is obtained by dividing the current density at a certain voltage by the amount of catalyst metal supported per unit area.

  The preferable conditions in the preparation process of the catalyst powder used for the electrode for PEFC of this invention are demonstrated below. First, a slurry-like dispersion is prepared by mixing a cation exchange resin solution and carbon. The carbon may be in the form of powder, granules or fibers, and a mixture thereof may be used.

  The carbon used in the present invention is preferably carbon black such as acetylene black or furnace black having high electron conductivity and a large surface area. Furthermore, various carbon materials such as carbon tubes, carbon horns, and carbon fibers can be used.

  The slurry dispersion in which the cation exchange resin solution and carbon are mixed is prepared, for example, by adding carbon to the cation exchange resin solution and then stirring, but the mixing method is not particularly limited. Any method may be used as long as the solution and carbon can be mixed. In this mixing process, the mixed solution and carbon can be more effectively mixed by irradiating the dispersion with ultrasonic waves.

  Next, a mixture containing a cation exchange resin and carbon is prepared. The mixture can be prepared by removing the solvent from the cation exchange resin solution and carbon dispersion described above. The mixture is obtained in the form of a sheet, lump or powder.

  When the mixture containing the cation exchange resin and carbon is in the form of a sheet, the dispersion containing the cation exchange resin solution and carbon is applied to a substrate such as a polymer sheet or metal foil and then dried. Obtained by. When the mixture containing the cation exchange resin and carbon is in the form of a lump, it can be obtained by drying the dispersion in a container or the like. Furthermore, when the mixture containing a cation exchange resin and carbon is in a powder form, it can be obtained by spray-drying the dispersion, or by pulverizing a sheet-like or lump-like mixture.

  Finally, a catalytic metal is applied to the mixture containing the cation exchange resin and carbon. In this step, first, a solution is prepared by dissolving a compound containing a catalyst metal cation in water or water containing an alcohol. As the compound, a cation containing a platinum group metal or a complex ion of a platinum group metal can be used.

For example, as the complex ion, [Pt (NH ₃ ) ₄ ] ²⁺ or [Pt (NH ₃ ) ₆ ] ⁴⁺ can be represented as platinum ammine complex ion, or [Ru (NH ₃ ) ₆ ] ²⁺ or [ Ru (NH ₃ ) ₆ ] ³⁺ is preferred. Alternatively, in addition to the ammine complex ion, a platinum group metal complex ion coordinated with a nitrate group or a nitroso group can be used.

  Next, after a mixture containing a cation exchange resin and carbon is immersed in the solution, the mixture is washed with deionized water and dried. By the immersion, the cation of the catalyst metal is adsorbed on the cation exchange resin contained in the mixture. The adsorption is due to an ion exchange reaction between the counter ion of the cation exchange resin and the cation of the catalytic metal. At that time, by using two or more types of cations to be ion-exchanged, two or more types of catalytic metal cations can be adsorbed to the mixture.

  By this washing, other than the cation adsorbed on the cation exchange resin contained in the mixture is removed. The cations removed include, for example, those adsorbed on carbon.

  Furthermore, the cation adsorbed on the cation exchange resin is chemically reduced. Since the reduction is suitable for mass production, a method using a reducing agent is preferable. In particular, a method in which gas phase reduction is performed with hydrogen gas or a gas containing hydrogen or a method in which gas phase reduction is performed with an inert gas containing hydrazine is preferable. Here, the gas containing hydrogen gas is preferably a mixed gas of hydrogen gas and an inert gas such as nitrogen, helium, or argon, and preferably contains 10 vol% or more of hydrogen gas.

  The catalyst powder for a fuel cell constituting the electrode of the present invention is prepared by the above procedure. The ion exchange capacity of the cation exchange resin contained in the powder can be determined according to the type of the cation exchange resin solution.

  Next, after preparing a high capacity catalyst powder comprising a cation exchange resin having a large ion exchange capacity value and a low capacity catalyst powder comprising a resin having a small value, the high capacity catalyst powder, The electrode for a fuel cell of the present invention can be produced by mixing the capacity type catalyst powder and the dispersion medium, and applying and drying the mixture.

  The mixing ratio of the high-capacity catalyst powder and the low-capacity catalyst powder can be arbitrarily selected. Under normal operating conditions, the mixing ratio is 60:40 to 40:60 by weight. Furthermore, it is preferable because the effect of suppressing the drying and flooding of the electrode is high.

  Furthermore, when the PEFC is operated under conditions where the humidification of the fuel or oxidant is low, it is preferable to increase the mixing ratio of the high capacity catalyst powder because the output performance and durability performance of the battery can be improved. Conversely, when the PEFC is operated under conditions where the fuel or oxidant is highly humidified, it is preferable to increase the mixing ratio of the low-capacity catalyst powder because the output performance and durability performance of the battery can be improved.

  As described above, in the electrode of the present invention, drying of the electrode is prevented by the high-capacity catalyst powder, and further, flooding of the electrode is suppressed by the low-capacity catalyst powder electrode, so that the output performance and durability of the PEFC including the electrode are reduced. It is considered that the performance is improved.

[Examples 1 to 4 and Comparative Examples 1 and 2]
[Example 1]
Hereinafter, specific examples of the present invention will be described using preferred embodiments. The procedure for producing the catalyst powder is as follows.

  After mixing 320 g of cation exchange resin solution A (concentration 5 mass%) having an ion exchange capacity of 0.92 meq / g dry resin, 160 g of ethanol and 160 g of deionized water, carbon black (Vulcan XC) was added to the solution. -72, manufactured by Cabot Corporation) is added and mixed with a vacuum mixer to prepare a dispersion. Further, the dispersion is irradiated with ultrasonic waves with an ultrasonic irradiation device, and then the dispersion is spray-dried. A powdery mixture was prepared.

Next, 35 g of the powdery mixture is immersed in 250 ml of a 50 mmol / l concentration [Pt (NH ₃ ) ₄ ] Cl ₂ aqueous solution for 6 hours or more, so that the proton conduction pathway of the cation exchange resin contained in the mixture is obtained. Was adsorbed with the cation [Pt (NH ₃ ) ₄ ] ²⁺ of the platinum ammine complex, and the mixture was thoroughly washed with deionized water and dried.

  Finally, the mixture is placed in a reducer and maintained in a hydrogen atmosphere at 150 ° C. for 6 hours, so that the catalytic metal is mainly on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface. A supported low volume catalyst powder A was prepared. In this catalyst powder, the weight of platinum supported was about 3.0 mass% with respect to the weight of carbon black.

  Next, under the same conditions as in the preparation of the low-capacity catalyst powder described above, except that the cation exchange resin solution X (concentration 5 mass%) having an ion exchange capacity of 1.11 meq / g dry resin was used. A high-capacity catalyst powder X in which a catalytic metal was mainly supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface was prepared. In this catalyst powder, the weight of platinum supported was about 3.6 mass% with respect to the weight of carbon black.

  A conductive porous layer having an electron conductive microporous layer on one surface of carbon paper (360 μm thick) was manufactured. The manufacturing procedure is as follows. After immersing the carbon paper in a polytetrafluoroethylene (PTFE) dispersion having a solid content of 10% by mass, the excess dispersion is removed with a filter paper, and then at room temperature for 2 hours and at 80 ° C. for 1 hour with a dryer. Dried.

  The carbon paper was coated and dried with a paste-like mixture for the electron conductive microporous layer, and then dried with a dryer at 350 ° C. for 1 hour. A mixture of 200 g of water, 15 g of carbon black (Vulcan XC-72, manufactured by Cabot) and 16.7 g of a PTFE dispersion with a solid content of 60% by mass was used as the mixture for the electron conductive microporous layer. .

  Further, an electrode was manufactured by forming a catalyst layer on the conductive porous layer. The manufacturing procedure is as follows. After applying and drying the paste-like mixture for the catalyst layer on the surface of the conductive porous body layer on which the electron conductive microporous layer was formed, it was vacuum dried at 100 ° C. for 2 hours.

The catalyst layer mixture was prepared by mixing 7.5 g of low-capacity catalyst powder A, 7.5 g of high-capacity catalyst powder and 32 g of 2-methylethylpyrrolidone (NMP) in a twin-screw rotary mixer for 30 minutes. Subsequently, 6.4 g of a PTFE dispersion having a solid content of 60% by mass was added to the mixture, followed by mixing with a twin-screw rotary mixer for 30 minutes. The amount of platinum supported on the catalyst layer was 0.06 mg / cm ² and the size of the electrode was 25 cm ² .

  Finally, a membrane / electrode assembly (MEA) was manufactured by heat-pressing the electrode and the cation exchange membrane. The joining procedure is as follows. First, after stacking in the order of electrode / cation exchange membrane / electrode, the laminate was pressed with a flat press and further heated to 145 ° C. and held for 5 minutes. The same specification manufactured in Example 1 was used for each electrode. As the cation exchange membrane, a Nafion 115 membrane manufactured by DuPont was used.

  The membrane was pretreated by boiling with dilute sulfuric acid at a concentration of 0.5 mol / l for 1 hour and then washing 5 times with deionized water. This MEA was used as the MEA of Example 1, and a polymer fuel cell (PEFC) of Example 1 having the MEA was manufactured.

[Example 2]
Under the same conditions as in the preparation of the low-capacity catalyst powder of Example 1, except that the cation exchange resin solution B (concentration 5 mass%) having an ion exchange capacity of 0.81 meq / g dry resin was used. A low-capacity catalyst powder B in which a catalytic metal was mainly supported on the contact surface between the proton conduction path of the ion exchange resin and the carbon surface was prepared. In this catalyst powder, the weight of platinum supported was about 2.7% by mass based on the weight of carbon black.

  Except for using the cation exchange resin solution Y (concentration 5 mass%) whose ion exchange capacity is 1.37 meq / g dry resin, under the same conditions as the preparation of the low capacity catalyst powder of Example 1, A high-capacity catalyst powder Y in which a catalytic metal was mainly supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface was prepared. In this catalyst powder, the weight of platinum supported was about 4.4 mass% with respect to the weight of carbon black.

  An MEA was produced in the same manner as in Example 1 except that the low-capacity catalyst powder B and the high-capacity catalyst powder Y were used, and a PEFC of Example 2 having this MEA was produced.

[Example 3]
An MEA was produced in the same manner as in Example 1 except that the low-capacity catalyst powder A and the high-capacity catalyst powder Y were used, and a PEFC of Example 3 having this MEA was produced.

[Example 4]
An MEA was produced in the same manner as in Example 1 except that the low-capacity catalyst powder B and the high-capacity catalyst powder X were used, and a PEFC of Example 4 having this MEA was produced.

[Comparative Example 1]
An MEA was prepared in the same manner as in Example 1 except that 15 g of low-capacity catalyst powder A and 32 g of 2-methylethylpyrrolidone (NMP) were used for the preparation of the catalyst layer mixture. Made PEFC.

[Comparative Example 2]
An MEA was prepared in the same manner as in Example 1 except that 15 g of high capacity catalyst powder X and 32 g of 2-methylethylpyrrolidone (NMP) were used for the preparation of the catalyst layer mixture. Made PEFC.

[Characteristics of PEFC]
The output performance and durability performance of the PEFCs of Examples 1 to 4 and Comparative Examples 1 and 2 were evaluated. The conditions for the evaluation are as follows. The cell temperature is 70 ° C., the humidification method is a bubbler humidifier, the humidification temperature of air and hydrogen is 70 ° C., the supply amounts of air and hydrogen are stoichiometric ratios of 2.5 and 1.25, and the current density is 250 mA / cm ^2. It was. Under this condition, the PEFC operates under fully humidified conditions.

  Under these conditions, cell voltage values were measured 100 hours and 1600 hours after the start of operation. The measured values are shown in Table 1. The table shows the cell voltage reduction rate per hour from 100 hours to 1600 hours. The decrease rate indicates the durability performance of PEFC, and the smaller the rate, the higher the durability performance.

表１から、１００時間後における比較例２のＰＥＦＣのセル電圧値は、実施例１〜４および比較例１のものよりも高いが、１６００時間後においてはその値が最も低くなった。言い換えると、比較例２のＰＥＦＣではセル電圧の低下が他のいずれの電池よりも大きいことがわかった。

From Table 1, the cell voltage value of PEFC of Comparative Example 2 after 100 hours was higher than that of Examples 1 to 4 and Comparative Example 1, but the value was lowest after 1600 hours. In other words, in the PEFC of Comparative Example 2, it was found that the cell voltage drop was larger than that of any other battery.

  As a result, since the ultra-small catalyst-carrying electrode of Comparative Example 2 contains only a cation exchange resin having a high ion exchange capacity value, the cell voltage is also increased due to the high proton conductivity of the resin immediately after the start of operation. Although it is high, on the other hand, it is considered that flooding occurs due to excessive accumulation of water in a resin having high water retention with the generation of water at the electrode due to continuous operation, and the cell voltage is significantly reduced. It is considered that the decrease rate of PEFC in Comparative Example 2 was increased due to the decrease in cell voltage accompanying flooding. This reduction in cell voltage has been a problem with conventional ultra-small catalyst supported electrodes.

  On the other hand, in Comparative Example 1, the cell voltage after 100 hours is lower than that of any other PEFC, but the cell voltage decrease rate is the smallest. This result is attributed to the fact that the ultra-small catalyst-carrying electrode of Comparative Example 1 contains only a cation exchange resin having a low ion exchange capacity value, and therefore flooding was suppressed due to the low water retention of the resin. It seems to do.

  Moreover, as can be seen from the rate of decrease in PEFC in Examples 1 to 4, by increasing the cell voltage after 100 hours by including a low-capacity catalyst powder and a high-capacity catalyst powder in the electrode, It can be seen that it is possible to achieve both a reduction in the cell voltage decrease rate during operation. This coexistence can be attributed to the fact that flooding is suppressed by the low-capacity catalyst powder at high humidification temperatures, and conversely, drying is suppressed by the high-capacity catalyst powder at low humidification temperatures.

  Next, a similar experiment was performed under the same conditions as above except that the humidification temperature of air and hydrogen was changed to 55 ° C. Under this condition, air and hydrogen are in a low humidified state. Under these conditions, cell voltage values were measured 100 hours and 1600 hours after the start of operation. Table 2 shows the cell voltage values and the rate of decrease.

表２と表１とを比較することによって、低い加湿温度では全てのＰＥＦＣのセル電圧が低下することがわかる。このセル電圧の低下は、電極および電解質膜の保水量が低減したことに起因するものと考えられる。

By comparing Table 2 and Table 1, it can be seen that the cell voltage of all PEFCs decreases at low humidification temperatures. This decrease in the cell voltage is considered to be caused by a decrease in the water retention amount of the electrode and the electrolyte membrane.

  In the case of Comparative Example 2 having a high-capacity catalyst powder with high water retention, it was found that the electrode operates relatively well even at low humidification because there is little decrease in the cell voltage accompanying the decrease in humidification temperature. .

  On the other hand, in the PEFC of Comparative Example 1, it can be seen that the cell voltage after 100 hours is low, and the cell voltage decrease rate is remarkably large. As a result, it was found that the durability of an electrode provided with an ion exchange resin having a low ion exchange capacity is remarkably lowered at a low humidification temperature.

  Further, as can be seen from the fact that the rate of decrease in PEFC in Examples 1 to 4 is less than half that in Example 1, it is possible to include low capacity catalyst powder and high capacity catalyst powder in the electrode. It was also found that the cell voltage reduction rate with continuous operation can be suppressed even at low humidification temperatures.

[Examples 5 and 6]
[Example 5]
An MEA was produced in the same manner as in Example 1 except that 3.5 g of the low capacity catalyst powder A, 3.5 g of the low capacity catalyst powder B, and 8 g of the high capacity catalyst powder X8 g were used. Made PEFC.

[Example 6]
An MEA was produced in the same manner as in Example 1 except that 7 g of the low-capacity catalyst powder A, 4 g of the high-capacity catalyst powder X4 g, and high-capacity catalyst powder Y4 g were used, and a PEFC of Example 6 equipped with this MEA was produced. .

[Characteristics of PEFC]
The output performance and durability performance of the PEFCs of Examples 5 and 6 were evaluated under the same conditions as in Example 1. The conditions for the evaluation were as follows: the battery temperature was 70 ° C., the humidification method was a bubbler humidifier, the humidification temperature of air and hydrogen was 70 ° C., the supply amounts of air and hydrogen were stoichiometric ratios of 2.5 and 1.25, current The density was 250 mA / cm ² .

  Under these conditions, the cell voltage values after 100 hours and 1600 hours from the start of operation were measured, and the measured values and the cell voltage decrease rate per hour from 100 hours to 1600 hours are shown in Table 3.

表３から、触媒粉末として、低容量形触媒粉末と高容量形触媒粉末とを３種類混合して用いた場合においても、セル電圧および1時間あたりのセル電圧の低下率は、低容量形触媒粉末と高容量形触媒粉末とを１種類づつ混合した実施例１〜４の場合と同様の、優れた特性を示した。

From Table 3, even when three kinds of low-capacity catalyst powder and high-capacity catalyst powder are mixed and used as the catalyst powder, the cell voltage and the rate of decrease in cell voltage per hour are low-capacity catalyst. The same excellent characteristics as in Examples 1 to 4 in which the powder and the high-capacity catalyst powder were mixed one by one were exhibited.

  As described above, the ultra-small catalyst-carrying electrode comprising the low-capacity catalyst powder and the high-capacity catalyst powder according to the present invention can suppress a decrease in cell voltage due to flooding during continuous operation, and has low humidification. It became clear that both high output performance and durability performance can be achieved even at temperatures. The fact that the operation is possible even when the humidification temperature is low can be said to be extremely effective for practical use of PEFC, such as simplifying the humidifier.

The schematic diagram of the catalyst by which the catalyst metal was mainly carry | supported by the contact surface of the proton conduction path | route of cation exchange resin, and the surface of carbon. The schematic diagram of an electrode provided with a low capacity type catalyst powder and a high capacity type catalyst powder.

Explanation of symbols

11 Carbon 12 Cation exchange resin 13 Proton conduction path of cation exchange resin (hydrophilic region)
14 Hydrophobic region 15 of cation exchange resin 15 Catalytic metal 21 Ultra-small catalyst supporting electrode 22 Catalyst layer 23 Conductive porous body 24 High capacity catalyst powder 25 Low capacity catalyst powder 26 Cation exchange membrane

Claims (3)

In a polymer fuel cell electrode having a catalyst layer containing a catalyst powder mainly supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface, the catalyst layer is cation exchange An electrode for a polymer fuel cell, comprising two or more kinds of catalyst powders having different ion exchange capacities of resins. 2. The polymer fuel according to claim 1, wherein the ion exchange capacity value of the cation exchange resin contained in the catalyst powder is 1 meq / g dry resin or more and less than 1 meq / g dry resin. Battery electrode. A polymer fuel cell comprising the polymer fuel cell electrode according to claim 1.

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