JP2006351320A - Manufacturing method of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a fuel cell capable of improving durability. <P>SOLUTION: This is the manufacturing method of a fuel cell 10 which has an electrolyte membrane 1, an anode catalyst layer 2a and a cathode catalyst layer 3a arranged on both sides of the electrolyte membrane 1, and a platinum deposition layer 6a arranged between the electrolyte membrane 1 and the anode catalyst layer 2a. The method comprises an electrolyte membrane/mixture layer formation process S12 in which a mixture layer 4 having platinum containing ions and/or a platinum containing complex and a proton conductive material is arranged on the anode catalyst layer 2a side of the electrolyte membrane 1 and a platinum deposition process S16 in which, after the electrolyte membrane/mixture layer formation process S12, the platinum contained in the platinum containing ions and/or platinum containing complex is deposited. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a fuel cell, and more particularly to a method for manufacturing a fuel cell capable of improving durability.

  A fuel cell is based on an electrochemical reaction in a membrane electrode assembly (hereinafter referred to as “MEA (Membrane Electrode Assembly)”) including an electrolyte and electrodes (cathode and anode) disposed on both sides of the electrolyte. The generated electric energy is taken out through separators disposed on both sides of the MEA. Among fuel cells, polymer electrolyte fuel cells (hereinafter referred to as “PEFC (Polymer Electrolyte Fuel Cell)”) used in household cogeneration systems and automobiles, etc., operate at low temperatures. This is possible and is typically used at operating temperatures of 80-100 ° C. In addition, PEFC has shown high energy conversion efficiency of 30 to 40%, has a short start-up time, and has a small and lightweight system. Therefore, PEFC has attracted attention as an optimal power source for electric vehicles and portable power sources.

  A unit cell of PEFC includes an electrolyte membrane, a cathode and an anode including a catalyst layer and a diffusion layer, and a separator, and the theoretical electromotive force thereof is 1.23V. In a normal PEFC, the catalyst layer includes carbon carrying platinum that functions as a catalyst for electrochemical reaction. In PEFC, the catalyst layer is based on an electrochemical reaction that occurs on the catalyst (platinum) of the cathode catalyst layer and the anode catalyst layer. To get an electromotive force. However, since the above electromotive force is not sufficient as a power source for an electric vehicle or the like, the fuel in the stack form is usually configured by arranging end plates or the like at both ends in the stacking direction of the stack in which unit cells are stacked in series. Batteries are being used.

  On the other hand, it is clear that hydrogen peroxide is generated in the anode catalyst layer in the unit cell during power generation of the fuel cell, and OH radicals originating from this hydrogen peroxide are the starting point, which deteriorates the polymer electrolyte of MEA. It is becoming. Such deterioration contributes to a decrease in the durability and power generation performance of the fuel cell. Therefore, by reducing the hydrogen peroxide in the MEA, the deterioration is suppressed and the durability and power generation performance of the fuel cell are improved. Is desired.

  Here, the hydrogen peroxide is supplied to the cathode, and oxygen that has permeated the electrolyte membrane (hereinafter referred to as “permeated oxygen”) is mainly reduced on the carbon of the anode catalyst layer. It is thought to be caused. On the other hand, if permeated oxygen is reduced on the anode platinum during power generation of the fuel cell, the amount of hydrogen peroxide produced can be reduced. Therefore, for example, if a platinum layer is interposed between the electrolyte membrane and the anode catalyst layer, permeated oxygen can be reduced by the platinum layer, so that the amount of hydrogen peroxide generated can be reduced. It is thought that it becomes.

Techniques relating to fuel cells including a platinum layer between an electrolyte membrane and an anode have been disclosed so far. For example, Patent Document 1 includes a step of forming a platinum layer by sputter etching on the surface of an uneven electrolyte membrane, and subsequently applying a mixture of carbon particles and an electrolyte solution to the surface of the platinum layer. A technique relating to a reaction layer forming method is disclosed.
JP-A-8-148176

  However, according to the technique according to Patent Document 1, platinum fine particles are used when the platinum layer is formed. Since platinum fine particles are an unstable substance, when a platinum layer is formed by this technique, there is a possibility that platinum aggregates during the layer formation. When platinum aggregates, there is a problem that it is difficult to obtain a sufficient hydrogen peroxide generation amount suppressing effect and it is difficult to improve the durability of the fuel cell.

  Then, this invention makes it a subject to provide the manufacturing method of the fuel cell which can improve durability.

In order to solve the above problems, the present invention takes the following means. That is,
The invention according to claim 1 includes an electrolyte membrane, an anode catalyst layer and a cathode catalyst layer disposed on both sides of the electrolyte membrane, and a platinum deposition layer disposed between the electrolyte membrane and the anode catalyst layer. An electrolyte membrane / mixture layer comprising a mixture layer comprising platinum-containing ions and / or a platinum-containing complex and a proton conductive material on the anode catalyst layer side of the electrolyte membrane According to a method of manufacturing a fuel cell, comprising: a production step; and a platinum precipitation step of depositing platinum contained in platinum-containing ions and / or platinum-containing complexes after the electrolyte membrane / mixture layer production step. Solve the above problems.

Here, in the present invention, the platinum deposition layer is a layer comprising precipitated platinum and a proton conductive material. The platinum-containing ions and / or platinum-containing complexes are not particularly limited as long as they can precipitate platinum in the platinum deposition step. Specific examples of platinum-containing ions include PtCl ₆ ²⁻ and Pt ^2+, and specific examples of platinum-containing complexes include Pt (NH ₃ ) ₄ Cl ₂ . Also, from the viewpoint of effectively depositing platinum, when platinum-containing ions are provided in the mixture layer, the protons contained in the proton conductive material are mixed in a form in which the platinum-containing ions are substituted. In the case where a platinum-containing complex is provided in the mixture layer, it is preferable that the proton-conducting material is impregnated with a platinum-containing complex dissolved in water. Further, in the present invention, the proton conductive material is not particularly limited as long as it has proton conductivity and can withstand the environment in the fuel cell, and specific examples thereof include a normal PEFC catalyst layer. Fluorine-based materials such as fluorinated resins and hydrocarbon-based materials used in the above.

  According to a second aspect of the present invention, in the fuel cell manufacturing method according to the first aspect, between the electrolyte membrane / mixture layer preparation step and the platinum deposition step, the anode catalyst layer and the both sides of the electrolyte membrane / mixture layer are provided. It comprises an electrolyte membrane / mixture / electrode preparation step in which a cathode catalyst layer is disposed.

  According to a third aspect of the present invention, in the fuel cell manufacturing method according to the first or second aspect, the platinum deposition step is a step of bringing a reducing agent into contact with the mixture layer.

  In the present invention, specific examples of the reducing agent include hydrogen gas.

  The invention according to claim 4 is a method of manufacturing a fuel cell comprising an electrolyte membrane, and an anode catalyst layer and a cathode catalyst layer disposed on both sides of the electrolyte membrane, wherein the anode catalyst layer contains at least platinum. And an electrolyte membrane / electrode preparation step in which an anode catalyst layer and a cathode catalyst layer are disposed on both sides of the electrolyte membrane, and a platinum deposition step of depositing platinum from the anode catalyst layer after the electrolyte membrane / electrode preparation step. The platinum deposition step comprises contacting a reducing agent with the cathode catalyst layer when the fuel cell is operating and an inert gas with the anode catalyst layer when the fuel cell is operating, so that the oxygen species are in contact with the cathode catalyst layer when the fuel cell is operating. The above problem is solved by a method for producing a fuel cell, which is a step of applying a potential fluctuation between a potential at which the reduction reaction occurs and a potential at which the reduction reaction does not occur.

  Here, in the present invention, platinum is a concept including platinum alone and a platinum-containing material (for example, platinum-containing ions, platinum-containing complexes, etc.). In the present invention, specific examples of the reducing material include hydrogen gas, and specific examples of the inert gas include nitrogen gas, rare gas typified by argon gas, helium gas, and the like. Can be mentioned. Furthermore, the potential fluctuation in the platinum deposition process is defined as an anode catalyst layer during fuel cell operation (hereinafter referred to as “FC anode catalyst layer”) and a cathode catalyst layer during fuel cell operation (hereinafter referred to as “FC anode catalyst layer”). It is referred to as “cathode catalyst layer”.), And the voltage is varied within a certain range (potential variation). If the potential fluctuation is a fluctuation that crosses a critical potential (for example, about 0.8 to 0.9 V) at which a reduction reaction of oxygen species (for example, water) occurs, the fluctuation range is not particularly limited. As a specific example thereof, a form in which the potential is changed between 0.7 V and 1.0 V can be exemplified. Here, 0.7V means a state in which the potential of the FC anode catalyst layer is 0.7V higher than that of the FC cathode catalyst layer, while 1.0V similarly indicates the potential of the FC anode catalyst layer. Is 1.0 V higher than the FC cathode catalyst layer.

  According to the first aspect of the present invention, platinum is deposited after disposing the mixture layer including the substance capable of depositing platinum between the electrolyte membrane and the anode catalyst layer, and between the electrolyte membrane and the anode catalyst layer. A platinum deposition layer is interposed. With this configuration, unlike the conventional technique in which a platinum layer is formed using platinum fine particles, it is possible to suppress the aggregation of platinum, so that the amount of hydrogen peroxide generated can be effectively suppressed. become. Therefore, according to the first aspect of the present invention, it is possible to provide a method of manufacturing a fuel cell capable of improving durability.

  According to the invention described in claim 2, after the anode catalyst layer and the cathode catalyst layer are disposed on both sides of the electrolyte membrane / mixture layer in which the mixture layer is disposed on the anode catalyst layer side of the electrolyte membrane, the platinum deposition layer Is formed. With such a configuration, platinum can be deposited from the mixture layer sandwiched between the anode catalyst layer and the electrolyte membrane, so that platinum can be deposited more uniformly. Therefore, according to the invention described in claim 2, it is possible to provide a method of manufacturing a fuel cell capable of further improving the durability.

  According to invention of Claim 3, in order to precipitate platinum by making the platinum containing ion and / or platinum containing complex and reducing agent with which a mixture layer is equipped react, it deposits platinum effectively by a simple method. It becomes possible to make it. Therefore, according to the invention described in claim 3, it is possible to provide a method of manufacturing a fuel cell capable of effectively improving durability.

  According to the fourth aspect of the present invention, platinum contained in the anode catalyst layer can be deposited at the interface between the anode catalyst layer and the electrolyte membrane. There is no need to intervene layers. Therefore, it is possible to deposit platinum at the interface between the anode catalyst layer and the electrolyte membrane while minimizing an increase in manufacturing steps. Therefore, according to the invention described in claim 4, it is possible to provide a method of manufacturing a fuel cell capable of improving durability while minimizing an increase in manufacturing steps.

  In PEFC, a hydrogen-containing gas (hereinafter referred to as “hydrogen”) is supplied to the anode, while an oxygen-containing gas (hereinafter referred to as “oxygen”) is supplied to the cathode. Electric energy generated by the electrochemical reaction of oxygen is extracted outside. In general, oxygen supplied to the cathode can be consumed by an electrochemical reaction at the cathode, but when the PEFC is operated, a phenomenon (crossover) occurs in which part of the oxygen passes through the electrolyte membrane and reaches the anode. On the other hand, since the anode during PEFC operation is at a low potential (for example, 0.1 V or less), there is a possibility that permeated oxygen is reduced and hydrogen peroxide is generated.

  A normal PEFC anode catalyst layer includes platinum that functions as a catalyst for an electrochemical reaction and carbon to carry the platinum, and the surface area of carbon in the catalyst layer is extremely larger than the surface area of platinum. When the permeated oxygen reaches the anode catalyst layer as described above, the permeated oxygen is more likely to come into contact with carbon than platinum. Here, when permeated oxygen is reduced on the carbon in the low potential environment, a two-electron reduction reaction occurs, so that a large amount of hydrogen peroxide is generated. On the other hand, when permeated oxygen is reduced on platinum in the same environment, the reduction reaction is mainly a four-electron reduction reaction, so that the production of hydrogen peroxide can be suppressed. Therefore, if the permeated oxygen can be brought into contact with platinum before the permeated oxygen comes into contact with the carbon of the anode catalyst layer, the amount of hydrogen peroxide produced can be reduced.

  The present invention has been made from such a viewpoint, and the gist of the present invention is to deposit platinum at the interface between the electrolyte membrane and the anode catalyst layer and bring the permeated oxygen into contact with the platinum, and the carbon and permeated oxygen in the anode catalyst layer. It is to reduce the amount of hydrogen peroxide produced by suppressing the contact of the water. If the amount of hydrogen peroxide produced can be reduced in this way, OH radicals produced from hydrogen peroxide can be reduced, and deterioration of the electrolyte membrane can be suppressed. Furthermore, if the platinum deposition layer is provided in the above-described form, even if a part of the permeated oxygen passes through the platinum deposition layer and reaches the anode catalyst layer, hydrogen peroxide is generated. When oxygen moves to the electrolyte membrane side, oxygen peroxide comes into contact with the platinum deposition layer. Here, since platinum has a hydrogen peroxide decomposition performance, the amount of hydrogen peroxide reaching the electrolyte membrane can be reduced if the hydrogen peroxide contacts the platinum deposition layer. Therefore, if the fuel cell having such a configuration is manufactured, it is possible to suppress the deterioration of the electrolyte membrane, so that the durability of the fuel cell can be improved. In addition, since the method according to the present invention is different from the conventional method in which a platinum layer is formed using platinum fine particles, it is possible to prevent aggregation of platinum, which is a concern when using platinum fine particles, and is uniform. It is possible to form a platinum deposition layer.

  The fuel cell manufacturing method of the present invention will be described more specifically below with reference to the drawings.

  FIG. 1 is a cross-sectional view schematically showing an example of a fuel cell manufactured by the method for manufacturing a fuel cell according to the first embodiment. In FIG. 1, the horizontal direction on the paper is the stacking direction of the catalyst layers. In the following description, “platinum” is described as a concept including platinum alone and platinum-containing materials (for example, platinum-containing ions, platinum-containing complexes, etc.).

  The illustrated fuel cell 10 includes an electrolyte membrane 1, an MEA 5 including an anode catalyst layer 2 a and a cathode catalyst layer 3 a disposed on both sides of the electrolyte membrane 1, and an electrolyte membrane 1 and an anode catalyst layer 2 a. An anode diffusion layer 2b and a cathode diffusion layer 3b disposed on both sides of the MEA 5, and an anode separator 7 and a cathode separator disposed outside the diffusion layers 2b and 3b. 8 and. .., And 8a, 8a,... Are formed on the surface of the separators 7 and 8 on the diffusion layer 2b, 3b side, while the cooling medium channel 7b is formed on the opposite surface. , 7b,..., 8b, 8b,. When the fuel cell 10 is operated, hydrogen is supplied to the anode 2 through the reaction gas passages 7a, 7a,..., And oxygen is supplied to the cathode 3 through the reaction gas passages 8a, 8a,. The The platinum deposition layer 6a was deposited from platinum-containing ions and / or platinum-containing complexes provided in the mixture layer disposed on the anode catalyst layer 2a side of the electrolyte membrane 1 in the manufacturing process of the fuel cell 10. It is a layer containing platinum (not shown).

  In the fuel cell 10 according to the present embodiment, the catalyst layers 2a and 3a are provided with platinum that functions as a catalyst during an electrochemical reaction, and the platinum deposition layer 6a has platinum deposition during steady operation of the fuel cell 10. Platinum deposited by the process is provided. The platinum deposition layer 6a plays a role of contacting permeated oxygen before the permeated oxygen supplied through the reaction gas flow paths 8a, 8a,... And permeating through the electrolyte membrane 1 reaches the anode catalyst layer 2a. The hydrogen peroxide generated by reducing a part of permeated oxygen that has passed through the platinum deposition layer 6a also plays a role of suppressing the electrolyte membrane 1 from reaching. Among these roles, the former reduces the amount of permeated oxygen reduced on the carbon of the anode catalyst layer 2a by bringing the platinum deposition layer 6a into contact with permeated oxygen and reducing the permeated oxygen on platinum. . If the amount of permeated oxygen reduced by the anode catalyst layer 2a is reduced in this way, the amount of hydrogen peroxide generated at the anode 2 can be reduced. On the other hand, in the latter, hydrogen peroxide generated in the anode catalyst layer 2a and the platinum deposition layer 6a are brought into contact with each other to decompose hydrogen peroxide and move from the anode catalyst layer 2a to the electrolyte membrane 1. The amount is reduced. Since the illustrated fuel cell 10 is provided with the platinum deposition layer 6a in such a form, the amount of OH radicals generated from hydrogen peroxide can be reduced. That is, according to the fuel cell 10 according to the present embodiment, it is possible to suppress deterioration of the electrolyte membrane due to OH radicals, and thus it is possible to improve durability.

Below, the method (platinum precipitation process) of depositing platinum from the said mixture layer is demonstrated.
The mixture layer includes a platinum-containing ion (PtCl ₆ ²⁻ ) and a proton conductive material (perfluorosulfonic acid polymer), and these protons are substituted by protons contained in the proton conductive material. Are mixed in the form. Therefore, in the present embodiment, for example, after the fuel cell 10 according to the illustrated embodiment is manufactured, platinum gas is deposited by supplying hydrogen gas as a reducing agent to the mixture layer and substituting platinum-containing ions and protons. To form a platinum deposition layer 6a. If hydrogen gas is supplied in this way, inevitably, after the mixture layer is disposed on the anode catalyst layer side of the electrolyte membrane (after the electrolyte membrane / mixture layer preparation step), the hydrogen gas as the reducing agent is reduced. Since it is supplied, the timing for supplying hydrogen gas is not particularly limited. On the other hand, when the fuel cell is operated, hydrogen is supplied to the reaction gas flow paths 7a, 7a,..., And the hydrogen reaches the mixture layer. Therefore, as a specific example of the timing for supplying hydrogen gas, a fuel cell can be operated.

  For convenience, in the above description, the mode in which hydrogen gas as a reducing agent is supplied after the fuel cell is manufactured is described. However, the reducing agent according to the present embodiment has a mixture layer disposed on the anode catalyst layer side of the electrolyte membrane. It is not particularly limited as long as it is supplied after being applied, and may be supplied to other occasions.

A process example of the method for manufacturing a fuel cell according to the present embodiment is shown in a simplified manner in FIG. 2, in order to prevent the drawing from becoming complicated, the anode 2, the cathode 3, the reaction gas channels 7 a, 7 a,..., 8 a, 8 a,..., The cooling medium channels 7 b, 7 b,. 8b, and the reference numerals of the fuel cell 10 are omitted.
As described above, the fuel cell according to this embodiment includes the electrolyte membrane, the mixture layer, the anode catalyst layer and the cathode catalyst layer, the anode diffusion layer and the cathode diffusion layer, and the anode separator and the cathode separator. Therefore, when manufacturing a fuel cell having such a configuration, for example, as shown in FIG. 2, first, an electrolyte membrane 1 is prepared (step S <b> 11), and a mixture layer 4 is formed on one surface of the electrolyte membrane 1. (Step S12: electrolyte membrane / mixture layer manufacturing step). Thereafter, the anode catalyst layer 2a and the cathode catalyst layer 3a are disposed on both sides of the electrolyte membrane / mixture layer produced in step S12 to produce the MEA 5 (step S13: electrolyte membrane / mixture / electrode production step). An anode diffusion layer 2b and a cathode diffusion layer 3b are disposed on both sides of the MEA 5 manufactured in step S13, and a membrane electrode diffusion layer assembly (hereinafter referred to as “MEGA”) 9 is manufactured (step S14). Then, the fuel cell is manufactured by disposing the anode separator 7 and the cathode separator 8 on both sides of the MEGA 9 manufactured in step S14 (step S15).

Here, in the manufacturing method according to the present embodiment, the platinum deposition layer is uniformly formed between the electrolyte membrane 1 and the anode catalyst layer 2a, thereby effectively suppressing the generation of hydrogen peroxide and the permeation of hydrogen peroxide. From the viewpoint of enabling suppression, the mixture layer 4 is disposed on one surface of the electrolyte membrane 1 (the surface on the anode catalyst layer 2a side), and then platinum is deposited. Therefore, as long as the said conditions are satisfy | filled, the platinum precipitation process (S16) which deposits platinum may be provided anywhere. That is, in the manufacturing method according to the present embodiment, the platinum deposition step is performed between step S12 and step S13, between step S13 and step S14, between step S14 and step S15, or after step S15. Can be provided in at least one or more locations. Therefore, “S16” is described in the portion of FIG. 2 where the platinum deposition step can be arranged. In FIG. 2, for convenience, the platinum deposition step S16 is arranged after step S14, and the embodiment of the manufacturing method in which the platinum deposition layer 6a is formed after step S14 is mainly illustrated.
In the above description, for convenience, the embodiment in which the anode catalyst layer 2a and the cathode catalyst layer 3a are disposed after the mixture layer 4 is disposed on the electrolyte membrane 1 is described. However, the manufacturing method according to the present embodiment is limited to the embodiment. For example, the mixture layer 4 is previously disposed on the surface of the anode catalyst layer 2a on the electrolyte membrane 1 side, and the anode catalyst layer with the mixture layer is disposed on the anode side of the electrolyte membrane. Form may be sufficient.

In the above description, the mixture layer having PtCl ₆ ²⁻ is described. However, platinum-containing ions that can be provided in the mixture layer are not limited to the ions, and may be ions that can precipitate platinum. Other ions may be used. Specific examples of the other ions include Pt ^{2+ and the} like.

Furthermore, in the above description, the mixture layer in a form provided with platinum-containing ions has been described, but the platinum-containing material that can be provided in the mixture layer is not limited to only platinum-containing ions, and together with the platinum-containing ions, Alternatively, a platinum-containing complex may be provided instead of the platinum-containing ion. Specific examples of the platinum-containing complex that can be provided in the mixture layer according to this embodiment include Pt (NH ₃ ) ₄ Cl ₂ .

  In addition, in the above description, the form in which the perfluorosulfonic acid polymer is provided as the proton conductive material has been described, but the proton conductive material that can be provided in the mixture layer is not limited to the polymer. Specific examples of the proton conductive material that can be provided in the mixture layer according to the present embodiment include a fluorine-based material such as a fluororesin used in a normal PEFC catalyst layer, and a hydrocarbon-based material. Can do.

  FIG. 3 is a cross-sectional view schematically showing an example of a fuel cell manufactured by the method for manufacturing a fuel cell according to the second embodiment of the present invention. In FIG. 3, the horizontal direction of the paper surface is the stacking direction of the catalyst layer, and parts having the same configuration as in FIGS. 1 and 2 are denoted by the same reference numerals as those used in FIGS. 1 and 2. Description is omitted.

  The illustrated fuel cell 20 includes an electrolyte membrane 1, an MEA 5 ′ including an anode catalyst layer 2a and a cathode catalyst layer 3a disposed on both sides of the electrolyte membrane 1, an anode diffusion layer 2b, a cathode diffusion layer 3b, MEGA 9 ′ including a platinum deposition layer 6b formed between the electrolyte membrane 1 and the anode catalyst layer 2a is provided. In the present embodiment, the platinum deposition layer 6b is formed by depositing platinum provided in the anode catalyst layer 2a in the platinum deposition step before the fuel cell 10 is operated. Therefore, the platinum deposition process according to this embodiment will be described below.

  In the fuel cell 20 according to the present embodiment, the platinum deposition layer 6b is formed by depositing platinum contained in the catalyst layer 2a. Therefore, in the fuel cell 20, there is no layer corresponding to the mixture layer 4 according to the first embodiment. Therefore, an example of the manufacturing process of the fuel cell 20 according to the present embodiment is shown in a simplified manner in FIG. 4, in order to prevent the drawing from becoming complicated, the anode 2, the cathode 3, the reaction gas channels 7 a, 7 a,..., 8 a, 8 a,..., The cooling medium channels 7 b, 7 b,. Reference numerals 8b,..., And the fuel cell 20 are omitted.

As shown in FIG. 4, in order to manufacture the fuel cell 20, first, the electrolyte membrane 1 is prepared (step S21), and the anode catalyst layer 2a and the cathode catalyst layer 3a are disposed on both sides of the electrolyte membrane 1. Then, the MEA 5 ′ is manufactured (step S22: electrolyte membrane / electrode manufacturing step). Thereafter, the anode diffusion layer 2b and the cathode diffusion layer 3b are arranged on both sides of the MEA 5 ′ produced in the step S22 to produce a MEGA 9 ′ (step S23). 7 and the cathode separator 8 are provided to manufacture a fuel cell (step S24). Here, the platinum deposition layer 6b according to this embodiment is formed at the interface between the anode catalyst layer 2a and the electrolyte membrane 1, and the platinum constituting the platinum deposition layer 6b originally exists in the anode catalyst layer 2a. . Therefore, in this embodiment, the platinum deposition step (S25) needs to be performed after the step S22. And like the case of the manufacturing method according to the first embodiment, the platinum deposition step (S25) may be provided anywhere after the step S22. However, as will be described later, in the platinum deposition step according to the present embodiment, an inert gas such as nitrogen gas is supplied to the anode catalyst layer 2a and hydrogen gas is supplied to the cathode catalyst layer 3a. A gas different from the gas supplied to 2a and 3a is supplied. That is, since the platinum deposition step according to the present embodiment and the operation of the fuel cell cannot be compatible, the manufacturing method according to the present embodiment needs to pass through the platinum deposition step before the operation of the fuel cell.
Therefore, in the manufacturing method according to the present embodiment, “S25” is illustrated as a portion where the platinum deposition step can be arranged. In FIG. 4, for convenience, the platinum deposition step S25 is arranged after step S24, and the embodiment of the manufacturing method in which the platinum deposition layer 6b is formed after step S24 is mainly illustrated.

Below, the form example of the platinum precipitation process which forms the platinum precipitation layer 6b concerning this embodiment is demonstrated.
In the manufacturing method according to the present embodiment, for example, after step S24, first, nitrogen is added to the anode catalyst layer 2a that functions as an anode when the fuel cell is operated (hereinafter simply referred to as “anode catalyst layer 2a”). In addition to flowing gas, hydrogen gas flows into the cathode catalyst layer 3a functioning as a cathode during the operation of the fuel cell (hereinafter simply referred to as “cathode catalyst layer 3a”) with full humidification (relative humidity 100%). . Here, “at the time of operation of the fuel cell”, focusing on only the platinum deposition step, the catalyst layer 2a into which nitrogen gas is introduced is the cathode, and the catalyst layer 3a into which hydrogen gas is introduced is the anode. This is to clarify the description based on the anode catalyst layer 2a and the cathode catalyst layer 3a when the fuel cell is operated.
In the platinum deposition step according to the present embodiment, a voltage is applied to the anode catalyst layer 2a and the voltage is changed while the gas is introduced, so that the potential of the anode catalyst layer 2a is 0 than the potential of the cathode catalyst layer 3a. Add a potential fluctuation that becomes higher in the range of 7 to 1.0V. In the present embodiment, for example, platinum eluted in the anode catalyst layer 2a at 1.0 V, which is the upper limit of the potential fluctuation, is precipitated by reacting with hydrogen gas that has permeated into the electrolyte membrane 1. The platinum layer formed by the deposition of platinum grows by the reaction with hydrogen gas and the potential drop to 0.7 V, which is the lower limit of the potential fluctuation. That is, the platinum deposition layer 6b is formed by repeatedly applying a potential fluctuation while flowing the gas. In the platinum deposition step, since hydrogen gas is supplied from the cathode catalyst layer 3a, platinum in the anode catalyst layer 2a comes into contact with the hydrogen gas from the surface on the electrolyte membrane 1 side. Therefore, platinum can be deposited on the electrolyte membrane 1 side of the anode catalyst layer 2a by the platinum deposition step, and the platinum deposition layer 6b can be formed at the site.

  In the present embodiment, the potential variation is such that the variation lower limit voltage (0.7 V in the above embodiment) and the variation upper limit voltage so as to cross a critical potential (for example, about 0.8 to 0.9 V) at which the reduction reaction of oxygen species occurs. (1.0V) may be set, and if the platinum deposition layer can be formed in a form capable of producing the above effect under the setting, the form of potential fluctuation, the time and cycle for applying the potential fluctuation, etc. It is not limited. FIG. 5 schematically shows an example of a potential variation when the variation lower limit voltage is set to 0.7V and the variation upper limit voltage is set to 1.0V.

  As shown in FIG. 5, examples of potential fluctuations in this embodiment include a pulse shape (see FIG. 5A), a digital shape (see FIG. 5B), and the like. In addition, from the viewpoint of improving the deposition efficiency of platinum, when the potential is varied by setting the above-described variation lower limit / upper limit voltage (0.7 to 1.0 V), the digital shape shown in FIG. It is preferable to vary the potential. On the other hand, as a specific example of the potential fluctuation time and cycle in the present embodiment, there can be mentioned a form in which about 10,000 cycles are changed in 24 hours. If the fluctuation time and cycle are in the range of 0.7 to 1.0 V, it is possible to form a platinum deposition layer having a form capable of producing the above-described effect.

  In the above description of the present embodiment, the case where the variation lower limit voltage is set to 0.7 V and the variation upper limit voltage is set to 1.0 V is described for the sake of convenience. The voltage is not limited to the above voltage as long as it is set so as to cross the critical potential (for example, about 0.8 to 0.9 V). Specific examples of the potential fluctuation range applicable in the present invention include 0.5 to 1.0 V, 0.7 to 1.2 V, and 0.5 to 1.2 V. In addition, for example, even if the potential fluctuation range is set only in a region higher than the potential at which the reduction reaction of oxygen species occurs (for example, set to 1.0 to 1.5 V), a platinum deposition layer can be formed. is there. However, if the potential is varied in such a range, the deposition rate of platinum increases rapidly compared to the above range, and the amount of platinum contributing to the electrochemical reaction may be significantly reduced in the anode catalyst layer. Further, since carbon contained in the catalyst layer may be dissolved, there is a concern that the power generation performance of the fuel cell is lowered. Therefore, from the viewpoint of producing a fuel cell capable of improving durability while securing a sufficient amount of platinum that contributes to the electrochemical reaction of the anode, it is in a form that crosses the potential at which the reduction reaction of oxygen species occurs. It is preferable to set a potential fluctuation range.

  In the above description, for the sake of convenience, a mode in which a fully humidified nitrogen gas is introduced is described. However, if the nitrogen gas is humidified to the extent that water as an elution destination of platinum can be present in the anode catalyst layer 2a, It may not be full humidification. However, from the viewpoint of improving the deposition efficiency of platinum, it is preferable to introduce a fully humidified nitrogen gas. From the viewpoint of facilitating elution of platinum and efficiently depositing a platinum deposition layer, the gas is preferably in a fully humidified state. On the other hand, the humidity of the hydrogen gas supplied to the cathode catalyst layer 3a is not particularly limited.

  Further, in the above description, for convenience, a mode in which nitrogen gas is allowed to flow into the cathode catalyst layer 3a has been described. However, the gas that is allowed to flow into the cathode catalyst layer 3a is not limited to nitrogen gas, but may be argon gas, helium gas, or the like. Alternatively, an inert gas such as a rare gas may be introduced.

  Further, in the above description, the platinum deposition step in which gas is introduced is described. However, the gas supply mode used when forming the platinum deposition layer in this step is not limited to this mode. These gases may be sealed on the cathode side and the anode side, respectively.

  In addition, in the above description, the embodiment in which the platinum deposition step is performed after the fuel cell including the MEGA 9 ′ including the MEA 5 ′ and the separators 7 and 8 is manufactured (after step S24) has been described. In the manufacturing method according to the present invention, if the platinum deposition step is provided after the MEA is manufactured (after the electrolyte membrane / electrode manufacturing step) and before the fuel cell is operated, the present invention is not limited to the above embodiment. Absent.

  In the above description, for convenience, a fuel cell including a single cell in which a reaction gas flow path is formed in the separator has been described. However, the form of the fuel cell to which the present invention can be applied is limited to the form. It is not a thing. No reaction gas flow path is formed in the separator, and it reacts with a diffusion layer formed by a porous material such as stainless steel, titanium or nickel, or a sintered metal produced by plating or foaming. The present invention can be preferably applied even to a fuel cell including a single cell in a form in which gas is supplied.

In the method of manufacturing a fuel cell according to the second embodiment, fully humidified nitrogen gas is allowed to flow into the anode catalyst layer, fully humidified hydrogen gas is allowed to flow into the cathode catalyst layer, the variation lower limit voltage is 0.7 V, and the variation upper limit is A partial cross-section of a platinum deposition layer formed when 30000 cycles of potential fluctuation with a voltage of 1.0 V over 3 days, and an anode catalyst layer disposed on both sides of the platinum deposition layer, and A partial cross section of the electrolyte membrane is shown in FIG. The illustrated cross section represents the result of observation with a scanning electron microscope (SEM). FIG. 6A shows a cross section before the platinum deposition step (initial interface), and FIG. 6B shows the result after the platinum deposition step. Cross sections are shown respectively. Note that the platinum deposition layer shown in FIG. 6 was formed by potential fluctuation of a digital waveform.
As shown in the figure, it is possible to form a platinum deposition layer at the interface between the anode catalyst layer and the electrolyte membrane by applying potential fluctuations under the above conditions. If the platinum deposition layer is formed in such a form, it becomes possible to effectively suppress the production of hydrogen peroxide at the interface between the anode catalyst layer and the electrolyte membrane. It is possible to decompose hydrogen peroxide that migrates from the layer to the electrolyte membrane. Therefore, according to the present invention, it is possible to improve the durability of the fuel cell.

It is sectional drawing which shows roughly the example of the form of a fuel cell manufactured by the manufacturing method of the fuel cell of this invention concerning 1st Embodiment. It is a figure which simplifies and shows the process example of the manufacturing method of the fuel cell concerning 1st Embodiment. It is sectional drawing which shows schematically the example of the form of a fuel cell manufactured by the manufacturing method of the fuel cell of this invention concerning 2nd Embodiment. It is a figure which simplifies and shows the process example of the manufacturing method of the fuel cell concerning 2nd Embodiment. It is the schematic which shows the example of a form of the electric potential fluctuation | variation concerning 2nd Embodiment. It is a cross-sectional photograph which shows a catalyst layer and an electrolyte membrane, and the platinum precipitation layer formed in these interfaces.

Explanation of symbols

S12 Electrolyte membrane / mixture layer preparation step S13 Electrolyte membrane / mixture / electrode preparation step S16, S25 Platinum deposition step S22 Electrolyte membrane / electrode preparation step 1 Electrolyte membrane 2a Anode catalyst layer 3a Cathode catalyst layer 4 Mixture layer 6a, 6b Platinum precipitation layer 10, 20 Fuel cell

Claims (4)

A fuel cell manufacturing method comprising an electrolyte membrane, an anode catalyst layer and a cathode catalyst layer disposed on both sides of the electrolyte membrane, and a platinum deposition layer disposed between the electrolyte membrane and the anode catalyst layer Because
An electrolyte membrane / mixture layer preparation step of disposing a mixture layer comprising platinum-containing ions and / or a platinum-containing complex and a proton conductive material on the anode catalyst layer side of the electrolyte membrane;
A platinum deposition step of depositing platinum contained in the platinum-containing ions and / or platinum-containing complex after the electrolyte membrane / mixture layer preparation step;
A method for producing a fuel cell, comprising: An electrolyte membrane / mixture / electrode preparation step is provided, wherein the anode catalyst layer and the cathode catalyst layer are disposed on both sides of the electrolyte membrane / mixture layer between the electrolyte membrane / mixture layer preparation step and the platinum deposition step. The method for producing a fuel cell according to claim 1, wherein: The method for producing a fuel cell according to claim 1, wherein the platinum deposition step is a step of bringing a reducing agent into contact with the mixture layer. A method of manufacturing a fuel cell comprising an electrolyte membrane, and an anode catalyst layer and a cathode catalyst layer disposed on both sides of the electrolyte membrane,
The anode catalyst layer contains at least platinum,
An electrolyte membrane / electrode manufacturing step of disposing the anode catalyst layer and the cathode catalyst layer on both sides of the electrolyte membrane;
A platinum deposition step of depositing the platinum from the anode catalyst layer after the electrolyte membrane / electrode preparation step,
In the platinum deposition step, a reducing agent is brought into contact with the cathode catalyst layer during operation of the fuel cell, and an inert gas is contacted with the anode catalyst layer during operation of the fuel cell. A method for producing a fuel cell, comprising a step of changing a potential between a potential at which a reduction reaction occurs and a potential at which a reduction reaction does not occur.

Images