JP2007157630A - Manufacturing method of membrane electrode conjugant, membrane electrode conjugant, and polymer electrolyte type fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a membrane electrode conjugant capable of obtaining easily and certainly the membrane electrode conjugant having an anode in which an excellent CO poisoning resistant property and an excellent electrode property can be obtained even when a carbon carrier of the catalyst layer of the anode is reduced (especially the carbon carrier is eliminated). <P>SOLUTION: The manufacturing method of the membrane electrode conjugant 9 comprises a first process in which the membrane electrode conjugant 9 having an anode 1A which contains as an electrode catalyst a particulate containing Pt and Ru as an constituent element is manufactured and a second process in which the potential of the anode 1A is maintained at a potential of +0.98 Vvs.SHE or higher. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a membrane electrode assembly, a membrane electrode assembly, and a polymer electrolyte fuel cell.

  A polymer electrolyte fuel cell is a system that converts chemical energy into electric power and heat simultaneously by electrochemically reacting a fuel gas containing hydrogen and an oxidant gas containing oxygen such as air. Polymer electrolyte fuel cells have been rapidly developed as a power source for household cogeneration systems and electric vehicles, with the improvement of energy problems and global environmental problems. Particularly in recent years, various studies have been conducted for the purpose of improving durability and exhibiting sufficient battery performance toward the practical application of polymer electrolyte fuel cells.

  Generally, a conventional polymer electrolyte fuel cell using a proton conductive polymer electrolyte is a catalyst-supported carbon obtained by supporting an electrode catalyst on a conductive carbon powder on both sides of a polymer electrolyte membrane. And a catalyst layer including a polymer electrolyte having hydrogen ion conductivity. Platinum or a platinum alloy is used as the electrode catalyst. A gas diffusion layer (such as carbon paper subjected to water repellent treatment) having both air permeability and electron conductivity is disposed on the outer surface of the catalyst layer. The combination of the catalyst layer and the gas diffusion layer constitutes a gas diffusion electrode, that is, an anode or a cathode.

  The fuel gas sent to the anode of a polymer electrolyte fuel cell, particularly a stationary polymer electrolyte fuel cell used as a power source for a cogeneration system, is obtained by desulfurizing natural gas and obtained by a steam reforming reaction. A mixed gas containing carbon oxide and hydrogen is used. By the way, when fuel gas mixed with a large amount of carbon monoxide gas is supplied to the anode, carbon monoxide is strongly adsorbed on the platinum catalyst of the anode, so that hydrogen is difficult to adsorb on the catalyst, and the electrode characteristics of the anode are reduced. The catalyst poisoning phenomenon of decreasing occurs.

  Here, even when carbon monoxide is mixed into the fuel gas, a catalyst having good durability against carbon monoxide that can suppress the deterioration of the electrode characteristics of the anode due to carbon monoxide has been demanded. A technique using a PtRu catalyst has been studied (see Non-Patent Document 1).

As these PtRu catalysts, those supported as fine particles on a carbon material having a large surface area are usually used, and synthesized, for example, by performing a heat treatment at 280 ° C. in a hydrogen atmosphere (see Non-Patent Document 2).
P. N. Ross, K.M. Kinoshita, A .; J. et al. Scarpelino and P.M. Stonehart, J.M. Electroanal. Chem 63, 97 (1975) Elsevier Sequoia S. A. , J .; Electroanal. Chem 229 (1987) 395-406

  However, even in a polymer electrolyte fuel cell having an anode catalyst layer containing a PtRu catalyst formed by the above-described heat treatment method in the prior art, in order to suppress degradation and degradation of the polymer electrolyte membrane, From the viewpoint of providing a polymer electrolyte fuel cell having good durability against carbon monoxide and further good power generation characteristics when reducing the amount of carbon (especially when eliminating the carbon support), there is still room for improvement. was there.

  More specifically, the peroxide generation reaction, which is one of the causes of degradation of the polymer electrolyte membrane, proceeds mainly on the carbon powder, and particularly at the anode electrode where the potential when the fuel cell is operating is low. Since peroxides such as hydrogen are more likely to be generated, the durability of the polymer electrolyte membrane and the membrane electrode assembly is greatly affected. On the other hand, in the case of using a PtRu catalyst such as PtRu black as an anode catalyst with the intention of suppressing decomposition degradation of the polymer electrolyte membrane, or in a catalyst having a high loading ratio of PtRu particles supported on carbon. By performing the heat treatment, the Pt particles, the Ru particles, or the Pt particles and the Ru particles may be combined to increase the particle size, and the anode electrode characteristics may be deteriorated. There is still room for improvement. It was.

The present invention has been made in view of the above viewpoint. Even when the carbon support of the catalyst layer of the anode is reduced (particularly when the carbon support is eliminated), it has good durability against carbon monoxide. Another object of the present invention is to provide a method for producing a membrane / electrode assembly, which can easily and reliably obtain a membrane / electrode assembly including an anode capable of obtaining good electrode characteristics.
Another object of the present invention is to provide a membrane / electrode assembly that is formed by the method for producing a membrane / electrode assembly of the present invention and that has both good durability against carbon monoxide and good power generation characteristics. And
Another object of the present invention is to provide a polymer electrolyte fuel cell comprising the membrane electrode assembly of the present invention as described above and having both good durability against carbon monoxide and good power generation characteristics. To do.

  As a result of intensive studies to achieve the above object, the present inventors achieve at least the following oxidation treatment on the anode of the membrane electrode assembly when producing the membrane electrode assembly. And the present invention has been reached.

That is, the present invention
A first step of producing a membrane electrode assembly having an anode containing fine particles containing Pt and Ru as constituent elements as an electrode catalyst;
The anode potential was set to +0.98 Vvs. A second step of maintaining the potential at SHE or higher,
A method for producing a membrane electrode assembly is provided.

  As described above, according to the present invention, after the membrane electrode assembly is produced in the first step, the anode side potential is increased to the potential at which Pt and Ru are dissolved in the second step.

  Thus, in the membrane electrode assembly manufactured by the method of the present invention, since the conventional heat treatment is not performed, the increase in the particle size of the metal catalyst can be suppressed by performing the heat treatment. . In addition, according to the present invention, after the membrane electrode assembly is manufactured, the activation process of the catalyst surface of the anode is performed in the second step, so that the operation can be facilitated. Furthermore, the operation in the second step of the present invention, that is, the electrochemical potential operation can be performed more easily and with higher accuracy than the heat treatment for temperature control. Therefore, good durability against carbon monoxide and good power generation characteristics even when the carbon support of the anode catalyst layer is reduced (especially when the carbon support is eliminated) from the viewpoint of suppressing decomposition degradation of the polymer electrolyte. Can be realized easily and reliably.

Here, in the present invention, “fine particles containing Pt and Ru as constituent elements” means (i) P
It is at least one of particles made of a mixture of t fine particles and Ru fine particles, (ii) particles made of an alloy of Pt and Ru, and (iii) a mixture of (i) and (ii). The particle size of the particles is not particularly limited as long as the effect of the present invention is obtained, but is preferably 10 nm or less from the viewpoint of obtaining the effect of the present invention more reliably.

  The detailed mechanism by which the above-described effects of the present invention can be obtained has not been clearly clarified, but the present inventors presume as follows.

  Hereinafter, standard redox potentials in which the redox potential pair is Ru and Ru oxide, and Pt and Pt oxide are shown.

RuO ₂ + 4H ⁺ + 4e ⁻ → Ru + 2H ₂ O +0.68 V (1)
RuO ₄ + 4H ⁺ + 4e ⁻ → RuO ₂ + 2H ₂ O +1.387 V (2)
PtO ₂ + 2H ⁺ + 2e ⁻ → PtO + H ₂ O + 1.045V (3)
PtO + 2H ⁺ + 2e ⁻ → Pt + H ₂ O +0.98 V (4)

  The actual oxidation-reduction potential varies somewhat depending on the temperature during the oxidation-reduction reaction, the concentration activity of the reductant and the oxidant, but fine particles (catalyst containing Pt and Ru as constituent elements as shown in the above formula (1). ) Surface Ru dissolution was +0.68 Vvs. Surfaces of fine particles (catalysts) that increase from a potential higher than SHE (“SHE” indicates a standard hydrogen electrode) (positive potential) and contain Pt and Ru as constituent elements as shown in the above formula (4) Dissolution of Pt was +0.98 Vvs. The potential increases from the potential above SHE (the potential on the + side).

  Therefore, by performing a potential sweep using a potential sweep means such as a potentiostat, the anode potential is set to +0.98 Vvs. If the temperature is raised to be higher than SHE, both Pt and Ru on the surface of fine particles (catalyst) containing Pt and Ru as constituent elements can be dissolved. Pt and Ru can be reprecipitated on the catalyst surface by adjusting the anode holding time and potential to the optimum conditions. Here, by carrying out dissolution and precipitation of Pt and Ru, adsorption of carbon monoxide is less likely to occur on the catalyst surface, and good electrode reaction characteristics can be obtained. (For example, a surface on which an arrangement state of Pt and Ru in which Ru atoms exist beside Pt atoms) can be formed.

  In the second step of the present invention, when “the potential of the anode is +0.98 Vvs. SHE or higher” is E1, from the viewpoint of facilitating the manufacturing work, hydrogen gas is flowed to the cathode as a reference electrode. The potential of the anode with respect to the cathode (reference electrode) may be adjusted to E1. In this case, strictly speaking, the potential of the cathode (reference electrode) does not completely match the theoretical SHE, but the present inventors have confirmed that even in this case, the effect of the present invention can be obtained. (Refer to Examples described later).

  In the present invention, after the second step, the anode potential is set to +0.68 Vvs. There is further provided a method for producing a membrane electrode assembly, further comprising a third step of maintaining the potential at SHE or lower.

  By further providing this third step, Pt and Ru dissolved from the catalyst surface in the second step can be more reliably re-deposited on the catalyst surface, and the good catalyst surface described above can be more reliably obtained. Can be formed. The present inventors believe that, by this third step, rearrangement of Pt and Ru on the catalyst surface can be performed more reliably, and the surface state can be changed to a state where adsorption of carbon monoxide is less likely to occur. .

  Furthermore, this invention provides the manufacturing method of the membrane electrode assembly characterized by repeating the said 2nd process and the said 3rd process.

  By repeating the second step and the third step in this way, it is more reliable that Pt and Ru dissolved from the catalyst surface in the second step are dissipated out of the catalyst layer (in the film or in the gas diffusion layer). While preventing, it is possible to more reliably and easily form a good catalyst surface having both the above-mentioned good durability against carbon monoxide and good power generation characteristics.

  The present invention also relates to a membrane electrode assembly comprising an anode, a cathode, and a polymer electrolyte membrane disposed between the anode and the cathode, and the production of the membrane electrode assembly of the present invention described above. A membrane electrode assembly is provided that is formed through a manufacturing method of any one of the methods.

  Since the membrane / electrode assembly of the present invention is produced through the production method of the membrane / electrode assembly of the present invention described above, when the carbon support of the catalyst layer of the anode is reduced (particularly when the carbon support is eliminated). Even so, it is possible to easily and surely obtain a membrane / electrode assembly including an anode capable of obtaining good durability against carbon monoxide and good electrode characteristics.

  The membrane / electrode assembly of the present invention can be used in the above-described membrane / electrode assembly of the present invention as long as the effects of the present invention can be obtained, that is, if the above-described good catalyst surface state can be realized. It may be manufactured by a method other than the manufacturing method.

  Furthermore, the present invention provides a polymer electrolyte fuel cell comprising the membrane electrode assembly of the present invention described above.

  Since the polymer electrolyte fuel cell of the present invention includes the membrane electrode assembly of the present invention described above, the carbon support of the anode catalyst layer is used from the viewpoint of suppressing decomposition degradation of the polymer electrolyte membrane. Even when the configuration is reduced (especially when the carbon support is eliminated), good durability against carbon monoxide and good electrode characteristics can be obtained at the same time.

According to the present invention, even when the carbon support of the anode catalyst layer is reduced (particularly when the carbon support is eliminated), good durability against carbon monoxide and good electrode characteristics can be obtained. It is possible to provide a method for producing a membrane electrode assembly capable of easily and reliably obtaining a membrane electrode assembly including an anode.
Further, even when the carbon support in the anode catalyst layer is reduced (particularly when the carbon support is eliminated) by the production method of the present invention, both good durability against carbon monoxide and good power generation characteristics are obtained. It is possible to provide a polymer electrolyte fuel cell having both a good durability against carbon monoxide and a good power generation characteristic, and a membrane electrode assembly having the membrane electrode assembly.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or an equivalent part, and the overlapping description may be abbreviate | omitted.

[First Embodiment]
FIG. 1 shows a first embodiment of a membrane / electrode assembly of the present invention (membrane / electrode assembly produced by the production method of the present invention) and an example of a basic configuration of a unit cell having the same (polymer of the present invention). 1 is a schematic cross-sectional view showing a first embodiment of an electrolyte fuel cell.

  1 includes a membrane electrode assembly 9, a gasket 6 a disposed around the anode 1 </ b> A of the membrane electrode assembly 9, and a gasket disposed around the cathode 1 </ b> C of the membrane electrode assembly 9. 6c, separator 4a and separator 4c arranged on both sides of membrane electrode assembly 9, current collector plate 7a arranged outside separator 4a, and current collector plate 7c arranged outside separator 4c, It is configured.

  First, the membrane electrode assembly 9 will be described. As shown in FIG. 1, the membrane electrode assembly 9 includes an anode 1A, a cathode 1C, and a polymer electrolyte membrane 1 disposed between the anode 1A and the cathode 1C.

  The polymer electrolyte membrane 1 is a solid electrolyte and has hydrogen ion conductivity that selectively transports hydrogen ions. In the membrane electrode assembly 9 during power generation, hydrogen ions generated at the anode 1A move through the polymer electrolyte membrane 1 toward the cathode 1C.

  The polymer electrolyte membrane 1 is not particularly limited, and a polymer electrolyte membrane mounted on a normal solid polymer fuel cell can be used. For example, a polymer electrolyte membrane made of perfluorocarbon sulfonic acid (for example, Nafion (trade name) manufactured by DuPont, USA, Flemion (trade name) and Asciplex (trade name) manufactured by Asahi Glass Co., Ltd., Japan Gore-Tex Co., Ltd.) Manufactured by GSII, etc.).

  Preferred examples of the cation exchange group of the polymer electrolyte membrane 1 include those having a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, and a sulfonimide group. From the viewpoint of proton conductivity, the polymer electrolyte membrane 1 preferably has a sulfonic acid group.

  The resin constituting the polymer electrolyte membrane having a sulfonic acid group is preferably a dry resin having an ion exchange capacity of 0.5 to 1.5 meq / g. It is preferable that the ion exchange capacity of the polymer electrolyte membrane is 0.5 meq / g dry resin or more because an increase in the resistance value of the polymer electrolyte membrane during power generation can be more sufficiently reduced, and the ion exchange capacity is 1.5 meq / g. It is preferable that it is less than g dry resin, since it is easy to sufficiently ensure good gas diffusion characteristics in the catalyst layer while keeping the moisture content of the polymer electrolyte membrane appropriately. From the same viewpoint as described above, the ion exchange capacity is particularly preferably 0.8 to 1.2 meq / g dry resin.

As the polymer _{electrolyte, CF 2 = CF- (OCF 2} CFX) m-Op- (CF 2) a perfluorovinyl compound represented by the n-SO ₃ H (m is an integer of 0 to 3, n is 1 represents an integer of 1 to 12, p represents 0 or 1, and X represents a fluorine atom or a trifluoromethyl group.) And a copolymer comprising a polymer unit based on tetrafluoroethylene It is preferable.

Preferable examples of the fluorovinyl compound include compounds represented by the following formulas (5) to (7). However, in the following formula, q is an integer of 1 to 8, r is an integer of 1 to 8, and t is 1 to 8.
An integer of 3 is shown.
_{CF 2 = CFO (CF 2)} q-SO 3 H ··· (5)
_{CF 2 = CFOCF 2 CF (CF} 3) O (CF 2) r-SO 3 H ··· (6)
_{CF 2 = CF (OCF 2 CF} (CF 3)) tO (CF 2) 2 -SO 3 H ··· (7)

  The polymer electrolyte membrane 1 may be composed of one or more types of polymer electrolytes.

  The polymer electrolyte membrane 1 may include a reinforcing body (filler) disposed in a state in which hydrogen ion conduction can be ensured from the viewpoint of ensuring sufficient mechanical strength. Examples of the material constituting such a reinforcing body include polytetrafluoroethylene and polyfluoroalkoxyethylene. Examples of the reinforcing body include a porous body having pores that can be filled with a polymer electrolyte (having hydrogen ion conductivity) or a fibrillar fiber.

  Fibril-like fibers are fibers in which fibrils (small fibers) existing on the surface are fluffed (fibrillated), and there are fine air grooves (holes) between each fibril. It refers to the fibers that are formed. For example, all cellulosic fibers are bundles of many fibrils, and there are fine air grooves (holes) between the fibrils.

  The cathode 1C is mainly composed of a cathode catalyst layer 2c disposed on one side of the polymer electrolyte membrane 1, and a cathode diffusion layer 3c disposed further outside the cathode catalyst layer 2c.

  The configuration of the cathode catalyst layer 2c is not particularly limited as long as the effects of the present invention can be obtained, and may have the same configuration as the catalyst layer of the gas diffusion electrode mounted on a known fuel cell. . For example, the cathode catalyst layer 2c may have a configuration including conductive carbon particles carrying an electrode catalyst and a polymer electrolyte having cation (hydrogen ion) conductivity. You may have the structure containing water-repellent materials, such as polytetrafluoroethylene. In addition, as a polymer electrolyte, the same kind as the constituent material of the polymer electrolyte membrane 1 mentioned above may be used, and a different kind may be used. As a polymer electrolyte, what was described as a constituent material of the polymer electrolyte membrane 1 can be used.

  The cathode electrode catalyst is made of metal particles (for example, metal particles made of a noble metal) and used by being supported on conductive carbon particles (powder). The metal particles are not particularly limited and various metals can be used, but from the viewpoint of electrode reaction activity, platinum, gold, silver, ruthenium, rhodium, palladium, osmium, iridium, chromium, iron, titanium, manganese It is preferably at least one selected from the group consisting of cobalt, nickel, molybdenum, tungsten, aluminum, silicon, zinc and tin.

  The electrode catalyst particles more preferably have an average particle size of 1 to 5 nm. An electrode catalyst having an average particle diameter of 1 nm or more is preferable because it is easy to prepare industrially, and if it is 5 nm or less, the activity per mass of the electrode catalyst is more easily secured, thereby reducing the cost of the fuel cell. Connection is preferable.

The conductive carbon particles preferably have a specific surface area of 50 to 1500 m ² / g. If the specific surface area is 50 m ² / g or more, it is easy to increase the supporting rate of the electrode catalyst, preferably because it can more sufficiently ensure the output characteristics of the resulting cathode catalyst layer 2c, a specific surface area of 1500 m ² / It is preferable that the pore size is not more than g because sufficiently large pores can be secured more easily and coating with a polymer electrolyte is facilitated, and the output characteristics of the cathode catalyst layer 2c can be more sufficiently secured. From the same viewpoint as described above, the specific surface area is particularly preferably 200 to 900 m ² / g.

  The conductive carbon particles preferably have an average particle size of 0.1 to 1.0 μm. When the thickness is 0.1 μm or more, gas diffusion in the cathode catalyst layer 2c can be more easily secured, and flooding can be prevented more reliably. In addition, when the average particle diameter of the conductive carbon particles is 1.0 μm or less, it becomes easy to easily make the electrode catalyst covered with the polymer electrolyte in a good state, and the electrode catalyst covered area with the polymer electrolyte is more increased. Since it becomes easy to ensure enough, it becomes easy to ensure sufficient electrode performance more and is preferable.

  As the cathode gas diffusion layer 3c, a conductive base material having a porous structure, which is made of a high surface area carbon fine powder, a pore former, carbon paper, carbon cloth, or the like in order to provide gas permeability. May be used. Further, from the viewpoint of obtaining sufficient drainage, a water repellent polymer such as a fluororesin may be dispersed in the cathode gas diffusion layer 3c. Further, from the viewpoint of obtaining sufficient electron conductivity, the cathode gas diffusion layer 3c may be made of an electron conductive material such as carbon fiber, metal fiber, or carbon fine powder.

  The anode 1A is mainly composed of an anode catalyst layer 2a disposed on the other side of the polymer electrolyte membrane 1, and an anode gas diffusion layer 3a disposed further outside the anode catalyst layer 2a. .

  The anode catalyst layer 2a has a configuration including a catalyst-supporting carbon obtained by supporting an electrode catalyst on carbon powder, and a polymer electrolyte having hydrogen ion conductivity. The anode electrode catalyst described above uses fine particles containing Pt and Ru as constituent elements in order to have good durability against carbon monoxide. Furthermore, the anode catalyst layer 2a is preferably configured to reduce the carbon support contained in the anode catalyst layer 2a from the viewpoint of suppressing decomposition degradation of the polymer electrolyte membrane due to peroxide, and does not contain a carbon support. Is more preferable. Here, the fine particles containing Pt and Ru as constituent elements contained in the anode catalyst layer 2a shown in FIG. 1 described above have a catalyst surface state in which carbon monoxide is unlikely to be adsorbed (for example, Ru atoms are adjacent to Pt atoms). Pt and Ru arrangement state as existing). This good catalyst surface can be formed by preferably adopting the first embodiment of the production method of the present invention described later.

Specifically, “fine particles containing Pt and Ru as constituent elements” included in the anode catalyst layer 2a are specifically (i) particles made of a mixture of Pt fine particles and Ru fine particles, and (ii) Pt and R
It is comprised from the particle | grains which consist of an alloy with u, and at least 1 type of the mixture of (iii) (i) and (ii). The particle size of the particles is not particularly limited as long as the effect of the present invention can be obtained, but is preferably 10 nm or less from the viewpoint of obtaining the effect of the present invention more reliably. More preferably, it is ˜5 nm. An electrode catalyst having an average particle diameter of 1 nm or more is preferable because it is easy to prepare industrially, and if it is 5 nm or less, the activity per mass of the electrode catalyst is more easily secured, thereby reducing the cost of the fuel cell. Connection is preferable.

The configuration of the anode gas diffusion layer 3a is not particularly limited as long as the effect of the present invention can be obtained, and has the same configuration as the gas diffusion layer of a gas diffusion electrode mounted on a known fuel cell. Also good. For example, you may have the same structure as the cathode gas diffusion layer 3c mentioned above.
The configuration of the anode gas diffusion layer 3a and the configuration of the cathode gas diffusion layer 3c may be the same or different.

  A pair of separators 4 a and 4 c for mechanically fixing the membrane electrode assembly 9 are disposed outside the membrane electrode assembly 9. The fuel gas is supplied to the membrane electrode assembly 9 on the inner surface of the separator 4a that contacts the gas diffusion layer 3a of the membrane electrode assembly 9, and the gas containing the electrode reaction product and unreacted reaction gas is reacted. A gas flow path 5a for carrying away from the field to the outside of the membrane electrode assembly 9 is formed. Further, the inner surface of the separator 4c that is in contact with the gas diffusion layer 3c of the membrane electrode assembly 9 supplies an oxidant gas to the membrane electrode assembly 9 and includes an electrode reaction product and an unreacted reaction gas. A gas flow path 5c for carrying gas away from the reaction field to the outside of the membrane electrode assembly 9 is formed.

  The gas flow paths 5a and 5c can be provided separately from the separator 4a and the separator 4c. However, in the fuel cell 10 of FIG. 1, the gas flow path 5a including the inner surface of the separator 4a and the groove provided on the inner surface of the separator 4c. 5c is employed.

  The separator 4a may have a configuration in which a cooling water flow path (not shown) including a groove provided by cutting or the like is formed on the outer surface on the side opposite to the membrane electrode assembly 9. Furthermore, the separator 4c may also have a configuration in which a cooling water flow path (not shown) including a groove provided by cutting or the like is formed on the outer surface on the side opposite to the membrane electrode assembly 9.

  Furthermore, as shown in FIG. 1, current collecting plates 7 a and 7 c having a role of collecting current from the separator may be provided on the outside of the pair of separators 4 a and 4 c by using metal plates plated with copper.

In this way, the membrane electrode assembly 9 is fixed between the pair of separators 4a and 4c, for example, the fuel gas is supplied to the gas flow path 5a of the separator 4a, and the oxidant is supplied to the gas flow path 5c of the separator 4c. By supplying the gas, an electromotive force of about 0.7 to 0.8 V can be generated in one fuel cell 10 when a practical current density of several tens to several hundred mA / cm ² is applied. However, usually, when a polymer electrolyte fuel cell is used as a power source, a voltage of several volts to several hundred volts is required, so in practice, the required number of fuel cells 10 are connected in series, It is used as a so-called stack (not shown). For example, a stacked body in which a plurality of fuel cells 10 are stacked is disposed between two end plates that are arranged to face each other, and used as a stack that is fastened.

  Next, a method for manufacturing the unit cell 10 shown in FIG. 1 (a first embodiment of a method for manufacturing a membrane electrode assembly of the present invention) will be described with reference to FIG. FIG. 2 is a process diagram showing an example of a manufacturing method of the unit cell 10 shown in FIG.

First, the first step of manufacturing a membrane electrode assembly having an anode using fine particles containing Pt and Ru as constituent elements as an electrode catalyst will be described. In this first step, a method of manufacturing a membrane electrode assembly using a known thin film manufacturing technique can be employed. For example, the cathode catalyst layer 2c can be formed by preparing a cathode catalyst layer forming paste exemplified below. That is, for example, carbon particles supporting 50 wt% of Pt are used as a catalyst, and a cation exchange resin solution, for example, a fluorine-based sulfonic acid polymer resin solution having the same quality as the polymer electrolyte membrane 1 (for example, a solid content of 10 wt% of the resin) The mixture of ethanol and water is gradually added, and carbon particles supporting Pt are mixed until the solid content of the resin per unit area of the catalyst is, for example, 2 mg / m ^2, thereby forming the cathode catalyst layer. To paste for.

  The amount of the cation exchange resin solution contained in the cathode catalyst layer forming paste varies depending on the specific surface area, pore size, and dispersibility of the carbon particles. The greater the specific surface area and the better the dispersibility, the greater the amount of resin. For example, the optimum resin amount decreases when the specific surface area is large due to pores that are so small that the resin cannot enter. For example, in the case of ketjen black, the optimum resin amount per unit g is 1.4 g / g. Further, if the type of carbon used is crystallized or graphitized, it is more desirable because it can suppress the oxidation of carbon.

  The anode catalyst layer 2a can be formed by adjusting an anode catalyst layer forming paste exemplified below. In the case of using catalyst-carrying carbon in which the anode electrode catalyst is carried on carbon powder, the anode catalyst layer forming paste carries fine particles containing Pt and Ru as constituent elements instead of the carbon particles carrying Pt. What is necessary is just to prepare by the method similar to the paste for cathode catalyst layer formation mentioned above except using a carbon particle.

  In the case where the carbon powder as the catalyst carrier is not contained, the cathode catalyst layer described above is used except that fine particles containing Pt and Ru as constituent elements are used instead of the carbon particles supporting Pt. What is necessary is just to prepare using the method similar to the paste for formation.

  More specifically, carbon particles supporting fine particles containing Pt and Ru as constituent elements as an electrode catalyst, preferably fine particles containing Pt and Ru as constituent elements, without containing carbon powder as a catalyst carrier, are anode electrodes. As a catalyst, a cation exchange resin solution, for example, a fluorinated sulfonic acid polymer resin solution having the same quality as the polymer electrolyte membrane 1 (for example, a solution in which a solid content of the resin is mixed in a mixed solution of ethanol and water) is used. Add gradually and prepare.

  When the catalyst-supported carbon in which the anode electrode catalyst is supported on carbon powder is used, the amount of the cation exchange resin solution contained in the anode catalyst layer forming paste is the same as that of the cathode catalyst layer forming paste described above. Can be used.

  Next, the cathode catalyst layer forming paste or the anode catalyst layer forming paste prepared by the manufacturing method described above is applied to a PP film with a bar coater and then dried. After drying, it is cut into a desired electrode size and transferred to the polymer electrolyte membrane by hot pressing to form the cathode catalyst layer 20c and the anode catalyst layer 20a. The method for forming the catalyst layer is not limited to this method, and a method for printing the catalyst layer paste on the film, a method for spraying the catalyst layer paste on the film, or the like may be used. At that time, the polymer electrolyte membrane used is not particularly limited, and as described above, a polymer electrolyte exchange membrane having a sulfonic acid group can be used.

  Further, gas diffusion layers 3a and 3c are laminated on the outside of the anode catalyst layer 20a or the cathode catalyst layer 20c, respectively, as shown in FIG. 2 using a conventionally known method. Further, a gasket 6a and a gasket 6c that prevent leakage and mixing of the supplied fuel gas and oxidant gas to the outside are disposed around the cathode 1C and the anode 1A with the polymer electrolyte membrane 1 interposed therebetween. The gasket 6a and the gasket 6c are previously integrated with the cathode 1C or the anode 1A and the polymer electrolyte membrane 1, and a combination of them may be referred to as a membrane electrode assembly 9.

  Next, as shown in FIG. 2, a pair of separator plates 4 a and 4 c provided with grooves so that gas flows are disposed outside the membrane electrode assembly 9, thereby constituting the unit cell 10. Here, current collector plates 7a and 7c are provided outside the pair of separators 4a and 4c, respectively. These 7a and 7c may be provided or may not be provided.

  Next, the anode potential is set to +0.98 Vvs. An example of the second step of maintaining the potential (E1) equal to or higher than SHE will be described.

  As shown in FIG. 2, in the second step, a potentiostat 30 is connected to the unit cell 10 manufactured by the above-described manufacturing method, and the anode 1A is the working electrode and the cathode 1C is the reference electrode. The electrochemical cell is constructed.

  Specifically, the potential of the anode with respect to the potential of the cathode 1C using the potentiostat 30 while flowing nitrogen gas through the anode 1A (working electrode 12) of the unit cell 10 and flowing hydrogen gas through the cathode 1C (reference electrode 11). +0.98 Vvs. The surface treatment is performed on the electrode catalyst of the anode catalyst layer 20a while maintaining the potential E1 equal to or higher than SHE. At this time, the holding time at E1 can be suitably adjusted as appropriate by a preliminary experiment or the like. The higher the E1 and the longer the time, the greater the elution amount of Pt and Ru as the anode catalyst and the amount of reprecipitation increases, but Pt and Ru reprecipitate on the electrode surface. This is because it is necessary to prevent the anode catalyst layer 20a from escaping outside the anode catalyst layer 20a (for example, in the polymer electrolyte membrane or in the gas diffusion layer), reducing the reaction area, and causing a decrease in voltage. .

  Next, hydrogen gas is supplied to the anode and a gas containing an oxidant gas is supplied to the cathode to perform normal power generation. Thereby, the potential of the anode can be lowered to the deposition potential of Pt and Ru as the anode catalyst. Pt and Ru dissolved in the second step are reprecipitated on the surface of the PtRu catalyst by the above-described potential treatment. That is, it is possible to easily form a good anode catalyst surface having good durability against the carbon monoxide shown in FIG.

[Second Embodiment]
Next, a second embodiment of the membrane electrode assembly of the present invention and a second embodiment of the polymer electrolyte fuel cell of the present invention will be described.

  The membrane electrode assembly and the polymer electrolyte fuel cell according to the second embodiment have the same configuration as that of the unit cell 10 shown in FIG. 1 except that the membrane electrode assembly and the polymer electrolyte fuel cell are manufactured using a manufacturing method described later. Yes. Hereinafter, the manufacturing method of this 2nd Embodiment is demonstrated using FIG.

  First, in the first step, a membrane electrode assembly and a polymer electrolyte fuel cell (unit cell) are formed in the same manner as the unit cell 10 of the first embodiment described above.

  Next, after the electrochemical cell similar to FIG. 2 described in the first embodiment is configured, nitrogen gas is allowed to flow through the anode 1A (working electrode 12) and hydrogen gas is allowed to flow into the cathode 1C (reference electrode 11). Using the potentiostat 30, the potential of the anode with respect to the potential of the cathode 1C is +0.98 Vvs. A second step of holding the potential E1 at SHE or higher is performed.

  Further, after the second step, the anode potential with respect to the potential of the cathode 1C is set to +0.68 Vvs. A third step of reducing the potential E2 to SHE or lower is performed. Here, after the third step, the potential of the anode with respect to the potential of the cathode 1C is set to +0.98 Vvs. A cycle operation that repeats the second step and the third step, such as performing the second step of raising the potential E1 to SHE or higher, may be performed.

  At this time, regarding the set potential and the number of times of repeating the second step and the third step, the greater the E1 potential, the greater the number of cycles, the greater the elution amount of Pt and Ru, and the greater the amount of reprecipitation. To do. However, Pt and Ru do not reprecipitate on the electrode surface, but dissipate outside the anode catalyst layer 20a (for example, in the polymer electrolyte membrane or in the gas diffusion layer), reducing the reaction area, From the viewpoint of preventing the decrease, it is preferable to appropriately set the upper limit potential or the number of times of repeating the second step and the third step by a preliminary experiment or the like. Also, the sweep speed is preferably set appropriately by a preliminary experiment or the like in consideration of the dissolved amount of Pt and Ru and the reprecipitation state of Pt and Ru.

  According to this embodiment, even when the carbon support of the anode catalyst layer is reduced (especially when the carbon support is eliminated), a good anode catalyst surface having good durability against carbon monoxide is more reliably ensured. Can be formed. Furthermore, it is possible to more easily and more reliably obtain a membrane electrode assembly including an anode capable of obtaining good durability against carbon monoxide and good electrode characteristics.

  As mentioned above, although embodiment of this invention was described in detail, this invention is not limited to the said embodiment.

  For example, in the first and second embodiments described above, between the anode gas diffusion layer 3a and the anode catalyst layer 2a shown in FIG. 1 and between the cathode gas diffusion layer 3c and the cathode catalyst layer 2c. May be provided with a water-repellent carbon layer composed of a water-repellent polymer and carbon powder. Thereby, water management in the membrane electrode assembly (water retention necessary for maintaining good characteristics of the membrane electrode assembly and quick drainage of unnecessary water) can be performed more easily and more reliably.

  Moreover, in the cell 10 of this invention, it is not necessary to provide the current collection board 7a arrange | positioned on the outer side of the separator 4a, and the current collection board 7c arrange | positioned on the outer side of the separator 4c.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these Examples at all.

Example 1
In this example, first, a unit cell having the same configuration as the unit cell of the polymer electrolyte fuel cell shown in FIG. 1 was produced except that the current collector plate 7a and the current collector plate 7b were not provided.

<First step>
PtRu black {HiSPEC6000: manufactured by Johnson Matthey Fuel Cell Japan, Pt / Ru = 1 (substance ratio), crystallite size 2.7 nm, specific surface area as anode catalyst (fine particles containing Pt and Ru as constituent elements) 73 m ² / (PtRu black 1 g)} and a cation exchange resin solution (“Nafion” manufactured by Aldrich Co.) were used to prepare an anode catalyst layer forming paste.

Next, as a cathode catalyst, PtC {HiSPEC 8000: manufactured by Johnson Matthey Fuel Cell Japan, Pt 50 wt%, crystallite size 3.7 nm, specific surface area 60 m ² / (PtC1 g)} and a cation exchange resin solution (Asahi Glass) The cathode catalyst layer forming paste was prepared using “Flemion” manufactured by Co., Ltd.

Next, the anode catalyst layer forming paste was applied to one main surface of the PP film with a bar coater and then dried. After drying, this PP film is cut into a size of 60 mm × 60 mm, and a dried paste layer is formed on one main surface of a polymer electrolyte membrane (manufactured by Gore, trade name “Gore Select”, film thickness: 30 μm). It was hot-pressed and transferred as described. In this way, an anode catalyst layer (Pt supported amount: 0.5 mg / cm ² ) was formed on one main surface of the polymer electrolyte membrane.

Next, the cathode catalyst layer forming paste was applied to one main surface of the PP film with a bar coater and then dried. After drying, this PP film is cut into a size of 60 mm × 60 mm and hot pressed so that the dried paste layer is placed on the other main surface of the polymer electrolyte membrane on which the anode catalyst layer is formed, Transcribed. In this way, a cathode catalyst layer (Pt supported amount: 0.5 mg / cm ² ) was formed on one main surface of the polymer electrolyte membrane. In this manner, a membrane catalyst layer assembly was produced.

  Next, gas diffusion layers were arranged on the outer surfaces on both sides of the membrane catalyst layer assembly, and a membrane electrode assembly was formed according to the procedure described below.

  That is, in order to form a gas diffusion layer, carbon paper (TGP-H-090 manufactured by Toray Industries, Inc.) having a size of 16 cm × 20 cm and a thickness of 250 μm was used, and an aqueous dispersion containing a fluororesin (Daikin Industries, Ltd.). After impregnating ND-1), the carbon cloth was dried to impart water repellency (water repellency treatment).

  Subsequently, a water repellent carbon layer was formed on one surface (entire surface) of the carbon cloth after the water repellent treatment. Conductive carbon powder (Denka Black (trade name) manufactured by Denki Kagaku Kogyo Co., Ltd.) and an aqueous solution (D-1 manufactured by Daikin Industries, Ltd.) in which fine powder of polytetrafluoroethylene (PTFE) is dispersed. By mixing, an ink for forming a water-repellent carbon layer was prepared. This water repellent carbon layer forming ink was applied to one surface of the carbon cloth after the water repellent treatment by a doctor blade method to form a water repellent carbon layer. At this time, a part of the water repellent carbon layer was embedded in the carbon cloth.

  Thereafter, the carbon cloth after the water repellent treatment and the formation of the water repellent carbon layer was baked at 400 ° C., which is a temperature equal to or higher than the melting point of PTFE, for 30 minutes. Finally, the central portion of the carbon cloth was cut with a punching die to obtain a gas diffusion layer with dimensions of 122.5 mm × 122.5 mm.

  Next, the membrane-catalyst layer assembly is sandwiched between two gas diffusion layers so that the central portion of the water-repellent carbon layer of the gas diffusion layer obtained as described above is in contact with the cathode catalyst layer and the anode catalyst layer, The whole was thermocompression-bonded with a hot press to obtain a membrane electrode assembly of the present invention.

Finally, a unit cell having the same structure as that shown in FIG. 1 was produced using the membrane electrode assembly of the present invention obtained as described above. The membrane electrode assembly is sandwiched between a separator plate having a gas flow path for supplying fuel gas and a cooling water flow path, and a separator plate having a gas flow path for supplying oxidant gas and a cooling water flow path, and both separator plates A gasket made of fluororubber was placed around the cathode and the anode, and a unit cell having an effective electrode (anode or cathode) area of 36 cm ² was obtained.

<Second step>
Next, a potentiostat (HA-151 manufactured by Hokuto Denko Co., Ltd.) was connected to the single cell produced in the first step by the same method as described above with reference to FIG. Next, nitrogen gas was supplied to the anode, hydrogen gas was supplied to the cathode, the potentiostat was operated, and the potential of the anode with respect to the cathode (reference electrode) was maintained at +1.1 V for 1 hour.
A single battery of Example 1 was obtained as described above.

<< Comparative Example 1 >>
A unit cell of Comparative Example 1 was produced in the same manner as the unit cell of Example 1 except that the treatment in the second step in Example 1 was not performed.

Example 2
In the same manner as in Example 1, a membrane electrode assembly and a polymer electrolyte fuel cell unit cell were produced.

<First step>
A unit cell was fabricated in the same procedure as in the first step in Example 1.

<Step of repeating the second step and the third step>
In the same procedure as the second step in Example 1, a potentiostat (HA-151 manufactured by Hokuto Denko Co., Ltd.) was connected to the single cell produced in the first step, and then nitrogen gas was supplied to the anode. Hydrogen gas was supplied to the cathode. Next, the potentiostat is operated, and the potential of the anode with respect to the cathode (reference electrode) is changed to five potential sweep processes with a potential sweep width of +1.1 V to +0.6 V and a potential sweep speed of 0.35 V / s ( A process of repeating a potential sweep from +1.1 V to +0.6 V and then performing a potential sweep in the reverse potential direction from +0.6 V to +1.1 V was performed five times).
A single cell of Example 2 was obtained as described above.

<< Comparative Example 2 >>
A unit cell of Comparative Example 1 was produced in the same manner as the unit cell of Example 2 except that the process of repeating the second step and the third step in Example 2 was not performed.

[Durability evaluation test for CO poisoning]
The durability test against CO poisoning of the unit cells obtained in Example 1 and Example 2 and Comparative Example 1 and Comparative Example 2 was performed according to the following procedure.

<Activation treatment>
The unit cells obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were controlled at 70 ° C., hydrogen gas was supplied as fuel gas to the anode-side gas flow path, and the cathode-side gas flow path was Each was supplied with air. At this time, the utilization rate of hydrogen gas was set to 70%, the utilization rate of air was set to 40%, and humidification was performed so that the dew points of hydrogen gas and air were about 70 ° C., respectively. Then, the cell was operated at an electric current density of 0.16 A · cm ⁻² for 100 hours for activation treatment (aging).

<Evaluation Tests 1-3>
In order to evaluate the durability of each unit cell against CO poisoning, the current density was set to 0.2 mA · cm ⁻² , air was supplied to the cathode, and the mixed gas {H ₂ + CO ₂ containing hydrogen as a main component to the anode. Each cell was operated under the same conditions as the above activation treatment except that (20%) + CO (20 ppm)} was supplied, and the output voltage of each cell after 30 minutes was recorded (Evaluation Test 1 ). Thereafter, the gas supplied to the anode was switched to a mixed gas whose composition was H ₂ + N ₂ (20%), and the output voltage of each unit cell after 300 minutes was recorded (Evaluation Test 2). Next, the gas supplied to the anode was switched to H ₂ gas, and the output voltage of each cell after 30 minutes was recorded (evaluation test 3). The results are shown in Table 1.

“ΔCO ₂ + CO” shown in Table 1 means the voltage of the unit cell obtained in the evaluation test 3 (anode supply gas: H ₂ , cathode supply gas: air) and the evaluation test 1 {anode supply gas: (H ₂ + CO ₂ (20%) + CO (20 ppm)), cathode supply gas: air}.

Further, “ΔN ₂ ” shown in Table 1 means the voltage of the unit cell obtained in the evaluation test 3 (anode supply gas: H ₂ , cathode supply gas: air) and the evaluation test 2 {anode supply gas: ( It is a voltage difference from the voltage of the unit cell obtained with H ₂ + N ₂ (20%), cathode supply gas: air Air).

Here, “ΔCO ₂ + CO” means each unit cell including the influence of poisoning of the anode electrocatalyst by CO and the effect of reducing the H ₂ concentration in the gas supplied to the anode from 100% to 80%. The amount of voltage drop is shown.

Therefore, the evaluation test 2, so as to have the same concentration of H ₂ with H ₂ concentration in the above-mentioned CO mixed gas supplied to the anode in Evaluation Test 1, the H ₂ + N ₂ gas and the N ₂ was added 20% feed By performing this test, it is possible to measure the voltage drop amount of each unit cell only due to the influence of the H ₂ concentration being lowered. Accordingly, “ΔCO ₂ + CO−ΔN ₂ ” shown in Table 1 is a value indicating only the voltage decrease amount due to CO poisoning of the anode electrode catalyst among the voltage decrease amounts of each unit cell. The smaller the value of “ΔCO ₂ + CO−ΔN ₂ ”, the higher the durability against CO poisoning.

As is clear from the results shown in Table 1 (particularly the value of “ΔCO ₂ + CO−ΔN ₂ ”), the unit cell of Example 1 that performed the second process in the present invention performed this process. It was confirmed that the durability against CO poisoning was about 2.4 times higher than the unit cell of Comparative Example 1 that was not present.

Further, as is clear from the results shown in Table 1 (particularly, the value of “ΔCO ₂ + CO−ΔN ₂ ”), the second process and the third process in the present invention were repeated in the second embodiment. It was confirmed that the unit cell had about three times higher durability against CO poisoning than the unit cell of Comparative Example 2 in which this treatment was not performed.

  As described above, the membrane electrode assembly and unit cell of Example 1 or the membrane electrode assembly and unit cell of Example 2 are used when the carbon support of the catalyst layer of the anode is reduced (particularly, the carbon support is eliminated). Even in this case, it was confirmed that it has both good durability against carbon monoxide and good power generation characteristics.

  The polymer electrolyte fuel cell produced by the production method of the present invention is suitably used as a main power source or auxiliary power source for a moving body such as an automobile, a distributed (on-site) power generation system (home cogeneration system), etc. Is expected to be.

1st Embodiment (membrane electrode assembly manufactured by the manufacturing method of this invention) of a membrane electrode assembly of this invention, and an example of the basic composition of a single cell provided with this (polymer electrolyte fuel cell of this invention) 1 is a schematic sectional view showing a first embodiment of FIG. It is process drawing which shows an example of the manufacturing method of the cell 10 shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolyte membrane, 2a ... Anode catalyst layer, 2c ... Cathode catalyst layer, 20a ... Anode catalyst layer before potential sweep process, 20c ... Cathode catalyst layer, 3a before potential sweep process ... Anode gas diffusion layer, 3c ... Cathode gas diffusion layer, 1A ... Anode, 1C ... Cathode, 4a ... Anode separator plate, 4c ... Cathode separator plate, 5a ... Fuel Gas channel, 5c ... Oxidant gas channel, 6a ... Anode gasket, 6c ... Cathode gasket, 7a ... Anode current collector plate, 7c ... Cathode current collector plate, 9 ... Membrane electrode assembly, 10 ... single cell, 11 ... reference electrode, 12 ... working electrode, 30 ... potentiostat.

Claims (5)

A first step of producing a membrane electrode assembly having an anode containing fine particles containing Pt and Ru as constituent elements as an electrode catalyst;
The potential of the anode is set to +0.98 Vvs. A second step of maintaining a potential equal to or higher than SHE;
Including,
A method for producing a membrane electrode assembly characterized by the above. After the second step, the anode potential is set to +0.68 Vvs. Further including a third step of maintaining the potential at SHE or lower;
The manufacturing method of the membrane electrode assembly of Claim 1 characterized by these. Repeating the second step and the third step;
The manufacturing method of the membrane electrode assembly of Claim 2 or 3 characterized by these. A membrane electrode assembly having an anode, a cathode, and a polymer electrolyte membrane disposed between the anode and the cathode,
Formed through the manufacturing method according to any one of claims 1 to 3,
A membrane electrode assembly characterized by the above. Comprising the membrane electrode assembly according to claim 4;
A polymer electrolyte fuel cell.

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