JP2006114382A - Fuel cell equipped with anode electrode and the electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent deterioration of an anode electrode in the case the electric potential of the anode electrode is elevated in a part of single cells constituting a fuel cell. <P>SOLUTION: In the anode electrode of the fuel cell, this is equipped with a catalyst metal that is installed dispersedly in this anode electrode and promotes a battery reaction, and a suppressing mechanism of elevation of an electric potential that suppresses the elevation of the electric potential in the catalyst metal locally at the time of electric potential elevation when the electric potential of the whole anode is elevated. Here, the catalyst metal is equipped in a state mixed with a solid polyelectrolyte having an ion exchange group that shows hydrophilicity and also realizes the proton conductivity. Furthermore, the suppressing mechanism of elevation of the electric potential suppresses the elevation of the electric potential locally in the catalyst metal by making the circumference of the catalyst metal develop a state that shows hydrophobicity locally at the time of the elevation of the electric potential. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an anode electrode and a fuel cell including the electrode.

  In order to maintain the power generation performance in the fuel cell, it is important to supply the gas without any delay to the electrode including the catalyst. Here, when the gas supply state is locally deteriorated in the fuel cell, not only the progress of the cell reaction is insufficient in the portion where the gas supply state deteriorates, but various inconveniences may occur. is there. For example, when hydrogen supply to the anode electrode is not sufficiently performed in some single cells constituting the fuel cell stack, the single cells (hydrogen-deficient cells) are separated from the surrounding normal cells connected in series. A voltage is applied. The voltage applied to the hydrogen-deficient cell works to advance the reaction of releasing electrons at the anode electrode of the hydrogen-deficient cell, but the normal battery reaction proceeds in the hydrogen-deficient cell where the supplied hydrogen is insufficient. As a result, the anode electrode of the hydrogen-deficient cell is in a high potential state. Thus, an undesirable reaction proceeds at the anode electrode of the hydrogen-deficient cell at a high potential.

  As an undesirable reaction that proceeds in the hydrogen-deficient cell, for example, elution of platinum (Pt), which is a catalyst metal included in the anode electrode, can be mentioned. Furthermore, when carbon is used as a carrier for supporting the catalytic metal, the oxidation of the carbon proceeds and water electrolysis can also occur. Since Pt and carbon are constituents of the anode electrode, if elution of Pt or oxidation of carbon occurs, the electrode structure of the fuel cell may be damaged and the catalytic metal may be reduced, leading to a decrease in fuel cell performance. There is. The oxidation reaction of carbon is shown in the following formula (1), the elution reaction of Pt is shown in the following formula (2), and the electrolysis of water is shown in the following formula (3).

C + 2H ₂ O → CO ₂ + 4H ⁺ + 4e ⁻ (1)
Pt → Pt ²⁺ + 2e ⁻ (2)
H ₂ O → (1/2) O ₂ + 2e ⁻ + 2H ⁺ (3)

  In order to prevent such inconvenience, for example, a configuration is known in which a catalyst for promoting electrolysis of water is further provided in addition to a catalyst for promoting a normal cell reaction in an anode electrode of a fuel cell (patent) Reference 1). By providing a catalyst that promotes electrolysis of water to actively carry out water electrolysis, the increase in the potential of the anode electrode is suppressed during hydrogen depletion, and other undesirable reactions such as Pt elution and carbon oxidation. Can be relatively suppressed.

Special table 2003-508877 gazette JP 2004-158387 A JP 2003-168442 A JP 2001-224969 A

  However, even if the degree of progress of reactions such as Pt elution and carbon oxidation is relatively suppressed as described above, these undesired reactions continue to proceed simultaneously with the electrolysis of water. Therefore, a technique for effectively suppressing deterioration of the electrode structure of the fuel cell has been desired.

  The present invention has been made to solve the above-described conventional problems, and prevents deterioration of the anode electrode when the potential of the anode electrode rises in some single cells constituting the fuel cell. Objective.

In order to achieve the above object, the present invention provides an anode electrode of a fuel cell,
A catalyst metal that is dispersed in the anode electrode and promotes a battery reaction;
The present invention includes a potential increase suppression mechanism that locally suppresses a potential increase in the catalytic metal when the potential of the entire anode electrode increases.

  According to the anode electrode of the present invention configured as described above, since the potential increase is locally suppressed in the catalyst metal when the potential is increased, the deterioration of the anode electrode caused by the emission of electrons by the catalyst metal is prevented. Can be suppressed. Therefore, the durability of the fuel cell can be improved, and the performance deterioration of the fuel cell can be prevented. Here, the increase in the potential of the entire anode electrode is caused by, for example, a decrease in the amount of hydrogen supplied to the fuel cell.

In the anode electrode of the present invention,
A solid polymer electrolyte having an ion exchange group that exhibits hydrophilicity and proton conductivity is provided in a state of being mixed with the catalyst metal,
The potential increase suppression mechanism may be configured to suppress the potential increase locally in the catalyst metal by setting the periphery of the catalyst metal to be in a state of hydrophobicity when the potential is increased.

  With such a configuration, when the potential rises, the periphery of the catalytic metal is locally hydrophobic, thereby suppressing the ion exchange group of the electrolyte that exhibits hydrophilicity from approaching the catalytic metal. Can do. Therefore, the potential difference between the catalyst metal and the electrolyte can be made smaller locally, and the potential increase in the catalyst metal can be locally suppressed.

In such an anode electrode of the present invention,
Comprising gold (Au) provided in the vicinity of the catalyst metal;
The electrolyte further includes a hydrophobic atomic group, and a thiol group (-SH) provided in the vicinity of the atomic group,
The potential increase suppression mechanism may be configured by the Au and the thiol group.

  With such a configuration, when the potential is increased, the thiol group provided in the vicinity of the hydrophobic atomic group is adsorbed to Au, so that the periphery of the catalytic metal in the vicinity of Au is locally made hydrophobic. It can be in the state shown.

 The specific structure in which the electrolyte has a hydrophobic atomic group in addition to the ion-exchange group and a thiol group provided in the vicinity of the atomic group includes, for example, a first side chain having an ion-exchange group And a second side chain having a hydrophobic atomic group and a thiol group. In such a case, ion exchange groups and thiol groups provided in different side chains can move relatively freely in the electrolyte. Therefore, when the potential is increased, the ion exchange group and the catalyst metal can be effectively separated.

The anode electrode of the present invention further includes
Gold (Au) provided in the vicinity of the catalyst metal;
A hydrophobic compound having a thiol group (-SH) and a hydrophobic atomic group;
With
The potential increase suppression mechanism may be configured by the Au and the thiol group.

  Even in such a case, when the potential rises, the thiol group provided in the vicinity of the hydrophobic atomic group is adsorbed to Au, so that the periphery of the catalytic metal in the vicinity of Au is locally hydrophobic. Can be in a state.

In the anode electrode of the present invention,
Comprising first carrier particles which are fine particles made of a substance having electron conductivity;
Both the catalyst metal and Au may be dispersedly supported on the first carrier particles.

  Thus, by supporting the catalyst metal and Au on the same first support, when the potential is increased and the thiol group is adsorbed to Au, the periphery of the catalyst metal is effectively made hydrophobic. Can do.

The anode electrode of the present invention further includes
It is good also as providing the water decomposition catalyst which accelerates | stimulates the decomposition reaction of water.

By providing the water splitting catalyst, when the potential rises, the water splitting catalyst can promote the water splitting reaction and generate electrons and protons at the anode. For this reason, in a fuel cell in which a plurality of unit cells are stacked, even if a state in which the potential increases in some unit cells continues, it is possible to continue power generation as a whole as a fuel cell. Here, the water decomposition catalyst may be a RuO _2.

In such an anode electrode of the present invention,
Second carrier particles, which are fine particles made of a substance having electron conductivity,
The second carrier particles may support the water decomposition catalyst without supporting the catalyst metal.

  As described above, even when the potential increase is locally suppressed in the catalyst metal when the potential is increased by supporting the water decomposition catalyst on the carrier particles different from the catalyst metal, the water decomposition catalyst has the effect. It is possible to proceed the decomposition reaction of water without receiving it.

  The present invention can be realized in various forms other than those described above. For example, the present invention can be realized in the form of a fuel cell including an anode electrode, a method for manufacturing an anode electrode, and the like.

Next, embodiments of the present invention will be described in the following order based on examples.
A. Fuel cell configuration:
B. Anode electrode manufacturing process:
C. Operation at the anode electrode:
D. Variations:

A. Fuel cell configuration:
FIG. 1 is a schematic cross-sectional view showing an outline of the configuration of a fuel cell as an embodiment of the present invention. The fuel cell of the present embodiment is a polymer electrolyte fuel cell, and FIG. 1 shows a single cell 10 that is a basic unit of the fuel cell. As shown in FIG. 1, the single cell 10 includes an electrolyte membrane 20, an anode electrode 21, a cathode electrode 22, gas diffusion layers 23 and 24, and separators 25 and 26.

  The electrolyte membrane 20 is a proton conductive ion exchange membrane formed of a solid polymer material, for example, a fluorine-based resin, and exhibits good conductivity in a wet state. In this example, a Nafion membrane (manufactured by DuPont) was used.

The anode electrode 21 and the cathode electrode 22 are layers formed on the electrolyte membrane 20, and include a catalytic metal that progresses an electrochemical reaction, an electrolyte having proton conductivity, and carbon particles having electron conductivity. ing. In this embodiment, platinum (Pt) is used as the catalyst metal. Further, as the electrolyte, a fluorine-based resin that conducts hydrated protons via a sulfonic acid group is used as the electrolyte membrane 20. Further, among the electrodes, the anode electrode 21 includes gold (Au) and ruthenium oxide (RuO ₂ ) as a water splitting catalyst in addition to Pt which is a catalyst metal. FIG. 2 is an enlarged schematic view showing the state of the anode electrode 21. As shown in FIG. 2, in the anode electrode 21, Pt and Au are supported on the same carbon particles, and RuO ₂ is supported on carbon particles different from the carbon particles on which Au and Pt are supported. ing. The carbon particles carrying the catalyst metal and the like are mixed with the electrolyte. Moreover, in addition to the sulfonic acid group in connection with proton conduction, the electrolyte with which the anode electrode 21 is provided further introduce | transduced the thiol group (-SH). Since the configuration of the anode electrode 21 corresponds to the main part of the present invention, the manufacturing method and operation of the anode electrode 21 will be described in detail later. The cathode electrode 22 does not have Au and a water decomposition catalyst, and is mixed with carbon particles supporting only the catalyst metal and an electrolyte in which no thiol group is introduced.

  The gas diffusion layers 23 and 24 are made of a member having gas permeability and electronic conductivity, and are formed of, for example, a metal member such as foam metal or metal mesh, or a carbon member such as carbon cloth or carbon paper. can do. Such gas diffusion layers 23 and 24 diffuse a gas to be subjected to an electrochemical reaction and collect current with an electrode including a catalyst.

  The separators 25 and 26 are formed of a gas impermeable conductive member. Separator 25, 26 can be formed with carbon members, such as dense carbon which made gas impermeable by compressing carbon, for example. Moreover, you may form by metal members, such as press-molded stainless steel.

  The separators 25 and 26 have a concavo-convex shape for forming a gas flow path in the single cell on the surface thereof. The separator 25 forms a single-cell fuel gas flow path 27 through which the fuel gas containing hydrogen passes between the separator 25 and the gas diffusion layer 23. Further, the separator 26 forms an in-single cell oxidizing gas passage 28 through which an oxidizing gas containing oxygen passes, between the separator 26 and the gas diffusion layer 24.

  A sealing member such as a gasket is provided on the outer periphery of the single cell 10 in order to ensure gas sealing performance in the single-cell fuel gas flow channel 27 and the single-cell oxidizing gas flow channel 28. A plurality of gas manifolds (not shown) through which fuel gas or oxidizing gas flows are provided on the outer periphery of the single cell 10 in parallel with the stacking direction of the single cells 10. The fuel gas flowing through the fuel gas supply manifold among the plurality of gas manifolds is distributed to each single cell 10 and passes through each single cell fuel gas flow path 27 while being subjected to an electrochemical reaction. Collect in the gas exhaust manifold. Similarly, the oxidant gas flowing through the oxidant gas supply manifold is distributed to each single cell 10, passes through the oxidant gas flow path 28 in each single cell while being subjected to an electrochemical reaction, and then collects in the oxidant gas discharge manifold. To do.

  As the fuel gas supplied to the fuel cell, a hydrogen-rich gas obtained by reforming a hydrocarbon-based fuel may be used, or a high-purity hydrogen gas may be used. For example, air can be used as the oxidizing gas supplied to the fuel cell.

In FIG. 1, only a single unit cell 10 is shown, but an actual fuel cell has a stack structure in which a plurality of unit cells 10 are stacked. For example, each separator on both sides
What is necessary is just to have the uneven | corrugated shape for forming the gas flow path in a single cell. In this case, the single-cell fuel gas flow path 27 is formed between the gas diffusion layer 23 in the predetermined single cell as the separator 25 on one side of the separator, and is adjacent as the separator 26 on the other side. A single-cell oxidizing gas flow path 28 is formed between the gas diffusion layer 24 and the single cell. Or in a stack structure, in order to adjust the internal temperature of a stack structure, you may provide the refrigerant | coolant flow path through which a refrigerant | coolant passes between each single cell or whenever a predetermined number of single cells are laminated | stacked. The refrigerant flow path can be provided between, for example, the separator 25 provided in one single cell and the separator 26 provided in the other single cell between adjacent single cells.

  Moreover, in FIG. 1, although the uneven | corrugated shape for forming the gas flow path in a single cell is provided in the separators 25 and 26, the shape of the gas flow path in a single cell can be set arbitrarily. For example, the separators 25 and 26 may be flat plate-like members having no uneven shape. In this case, the space formed inside the porous gas diffusion layer functions as a gas flow path in the single cell.

B. Anode electrode manufacturing process:
FIG. 3 is an explanatory diagram showing a manufacturing process of the anode electrode 21. When producing the anode electrode 21, first, carbon particles (carbon powder) are prepared (step S100). The carbon particles prepared in step S100 are carbon particles for supporting Pt and Au and carbon particles for supporting RuO ₂ as described above. In this embodiment, carbon black is used for supporting Pt and Au, and graphite is used for supporting RuO ₂ . Various carbon materials can be selected as the carbon material constituting the carbon particles, but the carbon particles for supporting Pt and Au have a higher surface area in order to increase the efficiency of the reaction promoted by the catalytic activity. It is desirable to choose one. Further, it is desirable to select carbon particles made of a carbon material having higher corrosion resistance as the carbon particles for supporting RuO ₂ . Graphite has high crystallinity and is particularly excellent in corrosion resistance.

  Next, Pt and Au are dispersed and supported on a part of the carbon particles (here, carbon black) prepared in step S100 (step S110). In order to carry Pt and Au, the carbon particles may be dispersed in a solution of a Pt compound and a solution of an Au compound, and an impregnation method, a coprecipitation method, or an ion exchange method may be performed. As the solution of the Pt compound, for example, an aqueous solution of platinum nitrate or chloroplatinic acid can be used. As the Au compound solution, for example, an aqueous solution of chloroauric acid can be used. In the case of the impregnation method, after the carbon particles are dispersed in the above solution, the solvent is evaporated and dried, and reduction treatment (firing in a reducing atmosphere) is performed. Either Pt and Au may be supported first, or may be supported on the carbon particles at the same time.

  The amount of Pt and Au supported on the carbon particles can be adjusted as the amount of Pt or Au contained in the solution of the compound used in the impregnation method. The amount of Pt supported can be, for example, an amount such that the ratio to the carbon particles is 20 to 60 wt%, and the amount of Au supported is, for example, an amount such that the ratio to the carbon particles is 10 to 40 wt%. be able to.

Next, RuO ₂ is dispersed and supported on carbon particles (here, graphite) different from those used in step S110 (step S120). When RuO ₂ is supported on carbon particles, carbon particles are dispersed in a Ru compound solution in the same manner as when Pt and Au are supported, and impregnation, coprecipitation, ion exchange, and the like are performed. Just do it. It is not necessary to perform a special oxidation step after Ru is supported on the carbon particles. If the anode electrode 21 is produced and incorporated in the fuel cell as described below using the carbon particles carrying Ru, the oxidation of Ru proceeds as the fuel cell generates power. The amount of RuO ₂ supported can be, for example, an amount such that the ratio to the carbon particles is 20 to 60 wt% in terms of the amount of Ru supported.

  Separately from the above-described supporting step, an electrolyte into which a thiol group is introduced is prepared (S130). In this embodiment, a perfluorosulfonic acid electrolyte is used as the electrolyte. The outline of the process for synthesizing the electrolyte of the example is shown in FIG. The process of electrolyte synthesis can be roughly divided into a process of synthesizing an ion exchange polymer, a process of substituting an ion exchange group of the ion exchange polymer with a sulfonyl group, and a process of introducing a thiol group into a site having the sulfonyl group. , Can be divided into

  The perfluorosulfonic acid electrolyte is synthesized by copolymerizing tetrafluoroethylene and a predetermined sulfonic acid film monomer. The ion exchange polymer thus obtained includes a main chain of a fluororesin and a hydrophobic side chain having a sulfonic acid group at the end. The ion exchange polymer in this example is shown in FIG. The ion exchange polymer thus formed functions as a normal solid polymer electrolyte as it is. Various solid polymers are known in which the length of the structural unit in the perfluoropolymer main chain having a repeating structure, the length of the side chain (number of repeating structural units), and the like are different.

In order to produce the electrolyte used in this example, a reaction for substituting a part of the sulfonic acid group at the side chain end of the ion exchange polymer with a sulfonyl group is performed. FIG. 4B shows a sulfonyl group-containing polymer in which a part of the sulfonic acid group is substituted with a sulfonyl group. This sulfonyl group-containing polymer is further provided with a halogen such as fluorine (F), chlorine (Cl), bromine (Br), iodine (I) in the sulfonyl group. For example, when F is contained, the side chain terminal of the polymer substituted from the sulfonic acid group becomes a sulfonyl fluoride group (—SO ₂ F).

  Thereafter, a thiol group is further introduced into the end of the side chain substituted with the sulfonyl group to complete the electrolyte of this example. When a thiol group is introduced, a substitution reaction is performed using a compound containing a thiol group and the same kind of halogen as that of the sulfonyl group. An example of the thiol group-containing compound used for the substitution reaction is shown in FIG. In addition, a product (electrolyte and halogen gas of this example) obtained by the above substitution reaction is shown in FIG.

  In the electrolyte of this example, when the sulfonic acid group included in the side chain of the ion-exchange polymer is substituted with a sulfonyl group, the thiol is finally converted by controlling the ratio of the sulfonic acid group substituted with the sulfonyl group. The proportion of side chains introduced can be adjusted. The ratio of substitution with the sulfonyl group can be performed by controlling the reaction time for substituting the sulfonic acid group with the sulfonyl group. The ratio of the sulfonic acid group to the thiol group at the side chain end of the electrolyte can be, for example, thiol group: sulfonic acid group = 1: 9 to 1: 1. Although the ratio of the thiol group may be equal to or less than the ratio of the sulfonic acid group, it is desirable that the ratio of the thiol group is small in order to maintain the activity of the electrochemical reaction.

  Note that the method for producing the electrolyte used in the anode electrode of this embodiment may be different. For example, first, a polymer having a sulfonyl group such as a sulfonyl fluoride group at the end of the side chain may be synthesized by copolymerizing tetrafluoroethylene and a predetermined monomer for a sulfonic acid film. . Thereafter, a part of the sulfonyl group may be substituted with a sulfonic acid group by hydrolysis, and a thiol group may be further introduced to the remaining sulfonyl group.

After producing the electrolyte in step S130, the carbon particles supporting Pt and Au in step S110 and the carbon particles supporting RuO ₂ in step S120 are dispersed in an appropriate organic solvent, and in step S130. The produced electrolyte is mixed to produce an electrode paste (step S140). And the said electrode paste is apply | coated on the electrolyte membrane 20 (step S150), and an anode electrode is completed. Application of the electrode paste onto the electrolyte membrane 20 can be performed, for example, by screen printing on the electrolyte membrane 20 using the electrode paste. Alternatively, a sheet may be formed by forming an electrode paste into a film, and this sheet may be hot pressed onto the electrolyte membrane 20.

  In order to fabricate the cathode electrode 22, an electrode paste using only Pt supported on carbon particles and using the Pt-supported carbon particles and an electrolyte not introduced with a thiol group (the previously described ion exchange polymer) is used. And this electrode paste may be applied onto the electrolyte membrane 20 in the same manner as the anode electrode 21.

C. Operation at the anode electrode:
When the fuel cell generates power, the reaction shown in the following formula (4) proceeds at the anode electrode 21 and the reaction shown in the following formula (5) progresses at the cathode electrode 22. The reaction shown in the formula (6) proceeds.

H ₂ → 2H ⁺ + 2e ⁻ (4)
(1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (5)
H ₂ + (1/2) O ₂ → H ₂ O (6)

FIG. 2 described above represents the state of the anode electrode 21 during normal operation in which the above-described reaction proceeds in the fuel cell. During normal operation, the reaction of the above formula (4) proceeds on Pt, which is a catalyst metal included in the anode electrode 21, using hydrogen supplied via the fuel gas flow path 27 in the single cell. Protons generated by the reaction of the formula (4) move in the anode electrode 21 toward the electrolyte membrane 20 in a hydrated state via the sulfonic acid group provided in the electrolyte in the anode electrode 21. Further, the electrons generated in the formula (4) move in the anode electrode 21 toward the gas diffusion layer 23 through the catalyst particles and the carbon particles supporting RuO ₂ . Note that the electrode potential of the anode electrode 21 during such normal operation is approximately 0 V (vs. RHE and RHE are reversible hydrogen electrode potentials).

  Hereinafter, the operation of the single cell 10 in the hydrogen deficient state will be described. FIG. 5 is an explanatory diagram showing the state of the anode electrode 21 when the amount of hydrogen supplied to the single cell 10 is reduced to be in a hydrogen deficient state. Even if a single cell 10 is in a hydrogen-deficient state, when other unit cells constituting the stack structure are generating power normally, the single cell in the hydrogen-deficient state is normal in the surroundings connected in series. A voltage is applied from the cell. Thus, the voltage applied from the surrounding normal cells works to advance the reaction of releasing electrons in the hydrogen-deficient single cell, but the normal battery reaction cannot proceed in the hydrogen-deficient cell. The anode electrode 21 of the hydrogen-deficient cell is in a high potential state. In such a hydrogen deficient state, the electrode potential of the anode electrode 21 is about 1.5 to 2.0 V (vs. RHE).

  When the electrode potential rises in this way, the thiol group introduced into the electrolyte is chemically adsorbed on Au carried on the carbon particles. A reaction in which a thiol group adsorbs to Au is shown in the following formula (7). With the reaction of the formula (7), electrons are released and the thiol group is adsorbed on Au. FIG. 5 shows a state in which the thiol group of the electrolyte is adsorbed on Au on the carbon particles. This reaction usually proceeds when the electrode potential is about 0.2 to 1.0 V (vs. RHE), and does not proceed during the normal operation described above.

_{-CF 2 CFSH + Au → -CF 2} CFSAu + H + + e - ... (7)

  In addition, when the thiol group of the electrolyte is adsorbed to Au on the carbon particles supporting Pt, the thiol group is provided at the end of the hydrophobic side chain, so the periphery of the carbon particles supporting Pt is locally (The state in which the periphery of Pt is locally hydrophobic is represented by drawing a region surrounded by a broken line as a hydrophobic region in FIG. 5 around Pt). Here, the side chain of the electrolyte having a sulfonic acid group related to proton movement at the end can move relatively freely in the wet electrolyte, but the hydrophilic sulfonic acid group has the above hydrophobic property. Since the region cannot be approached, the sulfonic acid group is microscopically separated from the catalyst metal. Thus, when the sulfonic acid group involved in proton conduction is separated from the catalyst metal, the potential rise is locally suppressed around the catalyst metal. Therefore, even in a hydrogen deficient state, the Pt elution reaction shown in the above-described formula (2) proceeds, or the carbon particles shown in the above-described formula (1) are oxidized in the carbon particles supporting the catalyst metal. The reaction does not proceed.

As described above, the potential rise is locally suppressed in the vicinity of the catalyst metal, but the electrode potential is high in the entire anode electrode 21 in a hydrogen-deficient state. At this time, the RuO ₂ that is a water splitting catalyst is already used. The water decomposition reaction shown in the above-described equation (3) proceeds. The water decomposition reaction hardly proceeds at the electrode potential when power generation is normally performed in the fuel cell, but actively proceeds when the electrode potential rises as in a hydrogen-deficient state. As shown in the formula (3), electrons and protons are released as the water decomposition reaction proceeds. Here, the water splitting catalyst is supported on carbon particles different from Pt and Au, and since the sulfonic acid group of the electrolyte can approach the vicinity of RuO ₂ , the proton generated by the water splitting reaction is , And passed to the electrolyte sulfonic acid group without any problem. The water used for the decomposition reaction is present in the electrolyte, and can also be supplied via a fuel gas containing hydrogen or supplied from the electrolyte membrane 20. Therefore, while the hydrogen deficiency state continues, the anode electrode 21 can continue the water decomposition reaction on the water decomposition catalyst while maintaining the state shown in FIG. Even in such a hydrogen-deficient state, as long as air is supplied without hindrance at the cathode electrode 22, the normal reaction shown in the equation (5) continues to proceed.

  When the supply state of hydrogen is restored in the single cell 10, the electrode potential is lowered at the anode electrode 21, and the normal electrochemical reaction is resumed. That is, since adsorption of thiol groups onto Au is a reversible reaction, the thiol groups dissociate from Au as the electrode potential decreases, making it possible for hydrophilic sulfonic acid groups to approach Pt. Normal reaction with hydrogen is resumed.

  According to the fuel cell of the present embodiment configured as described above, when a problem occurs in the supply state of the fuel gas partially in the fuel cell, and any one cell 10 is in a hydrogen-deficient state, In the anode electrode 21 of the single cell 10, an increase in potential can be suppressed locally around the catalyst metal. Then, by suppressing the potential increase locally around the catalyst metal, it is possible to suppress a reaction accompanied by the structural deterioration of the electrode. Therefore, even when a failure occurs in the fuel gas supply state partially in the fuel cell, the battery performance can be maintained and the durability of the fuel cell can be improved.

  In particular, since Pt and Au are supported on the same carbon particles, when the thiol group is adsorbed to Au, the periphery of Pt is sufficiently affected by the action of the hydrophobic side chain introduced at the end of the thiol group. Can be brought into a state of being hydrophobic. Therefore, the potential increase around the catalyst metal can be effectively suppressed.

  Further, in this embodiment, the water decomposition catalyst is positively performed in the hydrogen deficient state by providing the anode electrode 21 with a water decomposition catalyst. Unlike the Pt elution reaction and the carbon oxidation reaction, the water decomposition reaction is not accompanied by structural deterioration of the fuel cell. In addition, the water decomposition reaction is a reaction that can proceed when the electrode potential rises even when no water decomposition catalyst is provided. However, by providing a water decomposition catalyst, the water decomposition reaction can be carried out more actively. Can be advanced. By actively advancing the water decomposition reaction in this manner, even when the hydrogen deficiency state continues, electrons and protons are generated without advancing the reaction accompanied by the structural deterioration of the anode electrode 21, and the entire fuel cell As a result, it is possible to maintain the power generation state without any problem.

  Here, the water splitting catalyst is supported on carbon particles different from the carbon particles supporting Pt and Au. Therefore, when the electrode potential of the anode electrode 21 rises and the thiol group is adsorbed to Au, the water splitting catalyst is not affected by the adsorption reaction of the thiol group, and the surrounding state becomes particularly hydrophobic. Therefore, the activity of the water decomposition reaction can be effectively maintained.

Note that, in the case of carbon carrying RuO ₂ that supplies protons to the sulfonic acid group when the hydrogen deficiency state is reached, the state of high potential continues even after the thiol group is adsorbed to Au. In this embodiment, however, as RuO ₂ on carbon, in particular due to the use of high durability (less reactive) graphite, suppress the oxidation reaction of carbon in the RuO ₂ supported carbon particles progresses, the anode electrode 21 Deterioration of the structure can be suppressed.

  FIG. 6 shows the results of examining the performance of the fuel cell of this example when the fuel cell is in a hydrogen deficient state. In the figure, the graph shown as an example shows the result in the fuel cell of the present example including the anode electrode 21 described above. Further, the graph shown as a comparative example has the same configuration as the example, but the result in a fuel cell using an electrode that does not include Au and a water decomposition catalyst and does not have a thiol group introduced into the electrolyte as an anode electrode. Represents. The fuel cells of the example and the comparative example were each prepared in a single cell state, and an operation state (hydrogen depletion operation) in which a hydrogen deficiency state was obtained was repeatedly performed to examine changes in battery performance.

When obtaining the measurement results shown in FIG. 6, in the hydrogen-deficient operation, each single cell is installed at room temperature, 500 cc / min nitrogen is supplied to the anode side, and 500 cc / min air is supplied to the cathode side. However, the current was swept for 1 minute under the condition of 0.5 A / cm ² . In addition, as a normal power generation operation after the hydrogen depletion operation, while supplying 500 cc / min hydrogen to the anode side and supplying 500 cc / min air to the cathode side, the output current is 0.1 A / cm ² . The load was adjusted so that power was generated, and the output voltage was examined. FIG. 6 shows the results of measuring the output voltage during normal power generation operation while alternately repeating the above-described hydrogen deficient operation and normal power generation operation. The horizontal axis represents the number of times that the hydrogen depletion operation has been performed, and the vertical axis represents the output voltage during normal power generation operation after the number of times of hydrogen depletion operation. In FIG. 6, the results are shown as a graph in which output voltage values during normal power generation operation after a predetermined number of times of operation in a hydrogen deficient state are sequentially connected.

  As shown in FIG. 6, the output voltage gradually decreases in the fuel cell of the comparative example as the hydrogen deficient operation is repeated, whereas in the fuel cell of the present example, even if the hydrogen deficient operation is repeated, a high output is achieved. The voltage could be maintained. More specifically, in the fuel cell of the comparative example, when the hydrogen depletion operation is repeated about five times, the output voltage during the subsequent normal power generation operation is compared with the output voltage shown before the start of the hydrogen depletion operation. It decreased by about 30%. In contrast, in the fuel cell of the example, even when the hydrogen depletion operation is repeated about five times in the same manner, the output voltage during the normal power generation operation is almost the same as the output voltage shown before the start of the hydrogen depletion operation. The degree was maintained. This is considered to be because in the fuel cell of the example, the structural deterioration of the anode electrode 21 was suppressed during operation in a hydrogen-deficient state, and the deterioration of the cell performance could be prevented.

D. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

D1. Modification 1:
As the electrolyte included in the anode electrode 21, a solid polymer electrolyte of a type other than the perfluorosulfonic acid electrolyte may be used. For example, a hydrocarbon-based electrolyte can be used. An example of the hydrocarbon electrolyte is shown in FIG. FIG. 7 shows an aromatic polyetherketone sulfonic acid electrolyte. The electrolyte shown in FIG. 7 includes a main chain obtained by polymerizing polyether ether ketone, and a sulfonic acid group and a thiol group introduced into the main chain. Thus, if the electrolyte has a hydrophilic ion exchange group related to proton conduction and a thiol group provided on the hydrophobic side chain, the same effect can be obtained by using it instead of the electrolyte of the example. Can do.

  In the embodiment, the electrolyte provided in the anode electrode 21 and the electrolyte constituting the electrolyte membrane 20 are both perfluorosulfonic acid type electrolytes, but different types such as one electrolyte being a hydrocarbon type electrolyte. It is also possible to combine these electrolytes.

D2. Modification 2:
In the embodiment, the electrolyte included in the anode electrode has a side chain having a hydrophilic group related to proton conductivity and a hydrophobic side chain having a thiol group, but may have different configurations. For example, an electrolyte having a hydrophilic ion exchange group is used as the electrolyte, and separately from this electrolyte, a hydrophobic compound having a thiol group and a hydrophobic atomic group is further prepared, and both are mixed to form an anode electrode May be produced. Also in this case, when the potential of the anode electrode as a whole increases, the thiol group is adsorbed to Au in the vicinity of the catalyst metal and the periphery of the catalyst metal becomes locally hydrophobic, so that the electrolyte is provided. It is possible to prevent the hydrophilic ion exchange group from approaching the catalyst metal and obtain the same effect. Even in this case, the electrolyte has a hydrophilic group at the end of the side chain, and the hydrophobic compound also has a thiol group on the side chain composed of a hydrophobic atomic group. It is desirable that the degree is secured.

D3. Modification 3:
Further, as the water splitting catalyst, a type of water splitting catalyst other than RuO ₂ may be used. For example, nickel (Ni), iron (Fe), lead dioxide (PbO ₂ ), or the like can be used.

  Further, a configuration in which the water splitting catalyst is not supported on a carrier such as carbon particles is also possible. For example, a water splitting catalyst may be prepared without being supported on a carrier, and an electrode material paste may be prepared together with carbon particles supporting a catalytic metal and Au to form an anode electrode. If the water splitting catalyst can be disposed in the anode electrode with a sufficient distance from the catalyst metal, the same effect can be obtained.

D4. Modification 4:
Furthermore, it can also be set as the anode electrode which does not have a water splitting catalyst. It is more preferable that the anode electrode has a water splitting catalyst because electrons and protons can be continuously generated even when the hydrogen-deficient state continues. However, even without having a water splitting catalyst, it is possible to obtain an effect of suppressing potential rise locally around the catalytic metal and suppressing undesirable reactions that lead to structural degradation. A sufficient effect of maintaining the battery performance can be obtained.

D5. Modification 5:
The catalytic metal provided in the anode electrode is preferably Pt because of its high activity, but an alloy containing Pt such as Pt—Ru or other types of precious metals may be used. In addition, it is also possible to use Au as a catalyst metal and to have a function of promoting a battery reaction and a function of attracting a thiol group when hydrogen is deficient.

D6. Modification 6:
Further, the carrier supporting the catalyst metal, Au, and the water splitting catalyst is not limited to carbon particles, and other types of carriers such as ceramic particles having electron conductivity may be used. The durability of the anode electrode can be further improved if the carrier is made of a material that does not easily deteriorate due to oxidation or the like when the electrode potential rises.

D7. Modification 7:
In the anode electrode of the example, an electrolyte that conducts protons by sulfonic acid groups is used, but a different type of electrolyte may be used. For example, an electrolyte that includes a carboxylic acid group and conducts proton conduction by the carboxylic acid group may be used. As in the examples, if the ion exchange group involved in proton conduction in the electrolyte is hydrophilic, the thiol group provided in the vicinity of the hydrophobic group is adsorbed to Au, and the periphery of the catalyst metal is made hydrophobic. Thus, similarly to the embodiment, the potential increase around the catalyst metal can be locally suppressed.

D8. Modification 8:
In the examples, the anode electrode of the present invention is used in a normal solid polymer fuel cell, but the anode electrode of the present invention can also be applied to, for example, a direct methanol fuel cell. Even in a direct methanol fuel cell, by using the anode electrode of the present invention, when the potential temporarily rises at the anode electrode of some single cells, the same thing can be achieved to suppress deterioration of the battery structure and battery performance. An effect can be obtained.

2 is a schematic cross-sectional view showing an outline of the configuration of a single cell 10. FIG. FIG. 3 is a schematic diagram illustrating an enlarged state of an anode electrode 21. 5 is an explanatory diagram illustrating a manufacturing process of an anode electrode 21. FIG. It is explanatory drawing which shows the outline | summary of the process for synthesize | combining the electrolyte of an Example. It is explanatory drawing showing the mode of the anode electrode 21 when it becomes a hydrogen deficient state. It is explanatory drawing which shows the result of having investigated the performance of the fuel cell when it was made into the hydrogen deficient state. It is explanatory drawing which shows an example of a hydrocarbon type electrolyte.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Single cell 20 ... Electrolyte membrane 21 ... Anode electrode 22 ... Cathode electrode 23, 24 ... Gas diffusion layer 25, 26 ... Separator 27 ... Fuel gas flow path in a single cell 28 ... Oxidation gas flow path in a single cell

Claims (17)

An anode electrode of a fuel cell,
A catalyst metal that is dispersed in the anode electrode and promotes a battery reaction;
An anode electrode comprising: a potential increase suppression mechanism that locally suppresses a potential increase in the catalyst metal when the potential of the entire anode electrode increases. The anode electrode according to claim 1, further comprising:
A solid polymer electrolyte having an ion exchange group that exhibits hydrophilicity and proton conductivity is provided in a state of being mixed with the catalyst metal,
The potential increase suppression mechanism suppresses a potential increase locally in the catalyst metal by causing the periphery of the catalyst metal to be locally hydrophobic when the potential increases. Anode electrode. The anode electrode according to claim 2, further comprising:
Comprising gold (Au) provided in the vicinity of the catalyst metal;
The electrolyte further includes a hydrophobic atomic group, and a thiol group (-SH) provided in the vicinity of the atomic group,
The potential increase suppressing mechanism is constituted by the Au and the thiol group. The anode electrode according to claim 3, wherein
The electrolyte includes a first side chain having the ion exchange group, and a second side chain having the hydrophobic atomic group and the thiol group. The anode electrode according to claim 2, further comprising:
Gold (Au) provided in the vicinity of the catalyst metal;
A hydrophobic compound having a thiol group (-SH) and a hydrophobic atomic group;
With
The potential increase suppressing mechanism is constituted by the Au and the thiol group. The anode electrode according to any one of claims 3 to 5, further comprising:
Comprising first carrier particles which are fine particles made of a substance having electron conductivity;
The catalyst metal and Au are both dispersed and supported on the first carrier particles. Anode electrode. The anode electrode according to any one of claims 2 to 6,
The ion exchange group is a sulfonic acid group. The anode electrode according to any one of claims 1 to 7, further comprising:
An anode electrode equipped with a water decomposition catalyst that promotes water decomposition reaction. The anode electrode according to claim 8, wherein
The water splitting catalyst is RuO ₂ An anode electrode. The anode electrode according to claim 8 or 9, further comprising:
Second carrier particles, which are fine particles made of a substance having electron conductivity,
The second carrier particles carry the water decomposition catalyst without carrying the catalyst metal. Anode electrode.   A fuel cell comprising the anode electrode according to claim 1. A fuel cell comprising an electrolyte layer, and an anode electrode and a cathode electrode provided on the electrolyte layer,
The electrolyte layer is a solid polymer electrolyte membrane having proton conductivity,
The fuel cell according to any one of claims 2 to 10, wherein the anode electrode is the anode electrode. A method for producing an anode electrode of a fuel cell, comprising:
(A) a step of supporting a catalyst metal that promotes a battery reaction and gold (Au) on fine particles having electron conductivity;
(B) A step of preparing an electrolyte including an ion exchange group that exhibits hydrophilicity and realizes proton conductivity, a hydrophobic atomic group, and a thiol group (-SH) provided in the vicinity of the atomic group. When,
(C) A method for producing an anode electrode, comprising the step of forming the anode electrode using a paste obtained by mixing the catalyst metal and the fine particles supporting Au and the electrolyte. A method for producing an anode electrode according to claim 13,
The step (b)
(B-1) A polymer having a hydrophobic side chain, having a sulfonic acid group as an ion exchange group at one end of the side chain and another end of the other side chain Preparing a polymer having a sulfonyl group,
(B-2) A method for producing an anode electrode comprising: introducing the thiol group into a side chain having the sulfonyl group. The method for producing an anode electrode according to claim 13 or 14, further comprising:
(D) comprising a step of preparing a water splitting catalyst;
In the step (c), in addition to the fine particles and the electrolyte, the water decomposition catalyst is further mixed together to produce the paste. A method for producing an anode electrode of a fuel cell, comprising:
(A) a step of supporting a catalyst metal that promotes a battery reaction and gold (Au) on fine particles having electron conductivity;
(B) providing an electrolyte comprising an ion exchange group that exhibits hydrophilicity and realizes proton conductivity;
(C) preparing a hydrophobic compound having a thiol group (-SH) and a hydrophobic atomic group;
(D) Production of an anode electrode comprising a step of forming the anode electrode using a paste obtained by mixing the fine particles supporting the catalytic metal and the Au, the electrolyte, and the hydrophobic compound. Method. The method for producing an anode electrode according to claim 16, further comprising:
(E) comprising a step of preparing a water splitting catalyst;
In the step (d), in addition to the fine particles, the electrolyte, and the hydrophobic compound, the paste is prepared by further mixing the water decomposition catalyst together.

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