JP2007335108A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell capable of suppressing deterioration of material at the time of lack of fuel. <P>SOLUTION: The fuel cell is provided with an MEA 5 having an anode 2 and a cathode 3 and an electrolyte membrane 1 arranged between the anode and the cathode, a first separator 6 arranged on the anode side, and a second separator 7 arranged on the cathode side. The first separator is formed of a porous carbon material, and a heating medium passage 9a in which a heating medium containing at least water can be circulated is provided on the first separator. A water electrolysis catalyst 10 is installed at least on the surface of the heating medium passage and a proton conductive material is provided in the first separator. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell, and more particularly to a fuel cell capable of suppressing material deterioration when fuel is scarce.

  2. Description of the Related Art A fuel cell is an electrochemistry in a membrane electrode assembly (hereinafter referred to as “MEA (Membrane Electrode Assembly)”) comprising an electrolyte membrane and electrodes (anode and cathode) disposed on both sides of the electrolyte membrane. Electrical energy generated by the reaction 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. Is possible. In addition, PEFC has attracted attention as an optimal power source for electric vehicles and portable power sources because of its high energy conversion efficiency, short start-up time, and small and lightweight system.

  A single cell of PEFC includes an electrolyte membrane, a cathode including at least a catalyst layer, and an anode, and a theoretical electromotive force thereof is 1.23V. However, since such low electromotive force is insufficient as a power source for electric vehicles and the like, usually, a single cell is laminated in series to form a laminated body, and end plates or the like are formed at both ends of the laminated body in the lamination direction. A stack-type PEFC formed by arranging the two is used. From the viewpoint of reducing the contact resistance and the like, in the stack type PEFC, fastening pressure is applied from both ends thereof.

An electrochemical reaction that is a source of electricity generation in PEFC proceeds, for example, in the following steps. First, hydrogen delivered to the anode is decomposed into hydrogen ions and electrons in the presence of a catalyst (for example, platinum-supporting carbon).
Anode side: H ₂ → 2H ⁺ + 2e ⁻ (Formula 1)
Then, the generated hydrogen ions (hereinafter sometimes referred to as “protons”) move to the cathode through the electrolyte membrane that exhibits ionic conductivity in a wet state. Since the electrolyte membrane has a property of allowing only ions to pass through, the generated electrons cannot pass through the electrolyte membrane and move to the cathode through an external circuit. In a fuel cell, electricity is generated by such movement of electrons. On the other hand, the oxygen delivered to the cathode reacts with protons and electrons that have moved to the cathode, thereby generating water.
Cathode side: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (Formula 2)

  By the way, when the PEFC is operated, the inside of the cell is in various gas states, so that the fuel (hydrogen) is depleted and the anode is exposed to a high potential state (for example, a potential state such as 1.5 V. The same applies hereinafter). There is a risk of being. When a high potential state is reached, the constituent material of the anode (for example, platinum, carbon, etc.) deteriorates and the performance of PEFC deteriorates. Therefore, it is desired to suppress material deterioration at the time of fuel shortage.

  Several techniques aimed at improving the performance of a fuel cell by suppressing material deterioration at the time of fuel shortage have been disclosed so far. For example, Patent Document 1 discloses a technique of mixing a water electrolysis catalyst with an electrode catalyst in order to prevent the anode catalyst support from being corroded at the time of hydrogen deficiency. It is said that the resistance to battery reversal can be made stronger.

  Patent Document 2 discloses that in a fuel electrode of a solid polymer electrolyte fuel cell, at least one reaction layer that contacts a solid polymer electrolyte membrane and advances a fuel cell reaction, and a diffusion layer, There is disclosed a technique relating to a fuel electrode of a solid polymer electrolyte fuel cell, characterized in that it comprises at least one water decomposition layer for electrolyzing the water. According to this technology, it is possible to provide a fuel electrode of a polymer electrolyte fuel cell that is unlikely to cause deterioration of electrode characteristics even when fuel deficiency occurs. The “polymer solid electrolyte fuel cell” in Patent Document 2 corresponds to the PEFC, and the “fuel electrode” corresponds to the anode.

Furthermore, Patent Document 3 discloses a technique related to a polymer electrolyte fuel cell provided with an electrode including a catalyst and a mixed conductive material having both electron-proton conductivity. A sulfonated polyaniline is illustrated. According to the polymer electrolyte fuel cell according to this technology, the reaction area inside the electrode is increased and higher performance is exhibited. Note that the “polymer electrolyte fuel cell” in Patent Document 3 corresponds to the PEFC.
Special table 2003-508877 gazette JP 2004-22503 A JP 2001-110428 A

  However, even if a water electrocatalyst is disposed in the electrode by the techniques disclosed in Patent Document 1 and Patent Document 2, if water supplied to the water electrocatalyst is insufficient, an electrolysis reaction of water occurs. This makes it difficult to suppress material deterioration.

  On the other hand, in the technique disclosed in Patent Document 3, the proton conductive polymer electrolyte and the catalyst are sufficiently and uniformly brought into contact with the problem that a sufficient reaction area cannot be secured at the interface between the electrode and the ion exchange membrane. The purpose of this is to provide a PEFC capable of increasing the reaction area inside the electrode and exhibiting higher performance. Patent Document 3 exemplifies sulfonated polyaniline. However, the problem of the present invention to be described later differs from the problem of the invention according to Patent Document 3, because Patent Document 3 does not describe anything about suppression of material deterioration at the time of fuel deficiency. There was a problem that it was difficult to suppress material deterioration.

  Then, this invention makes it a subject to provide the fuel cell which can suppress material deterioration at the time of fuel deficiency.

In order to solve the above problems, the present invention takes the following means. That is,
The invention described in claim 1 includes an anode (referred to as “anode catalyst layer” in the description of the following embodiment) and a cathode (hereinafter referred to as “cathode catalyst layer” in the description of the embodiment), and an anode and a cathode. An MEA including an electrolyte membrane disposed between the first separator, a first separator disposed on the anode side, and a second separator disposed on the cathode side, wherein the first separator is a porous carbon material The first separator is provided with a heat medium flow path through which a heat medium containing at least water can circulate, and a water electrocatalyst is disposed at least on the surface of the heat medium flow path. The above problem is solved by a fuel cell characterized in that a proton conductive material is provided inside one separator.

Here, the “porous carbon material” means a carbon material having a large number of pores capable of diffusing a reaction gas (hereinafter referred to as “hydrogen”) and water supplied to the anode. In the present invention, “the first separator is formed of a porous carbon material” means a water electrocatalyst disposed in the first separator according to the present invention, and a reverse osmosis membrane that can be disposed in the first separator. It means that the main component of the first separator, excluding the gas seal structure and the like, is a porous carbon material. Furthermore, the “heat medium flow path” is supplied to the single cell for the purpose of maintaining the electrolyte membrane in a predetermined temperature range (for example, 70 to 90 ° C., etc.) in order to express proton conduction performance. This means the route through which the heat medium can flow. Specific examples of the heat medium include a heat medium such as warm water, and a cooling medium such as cold water and LLC. In addition, the “water electrocatalyst” refers to a catalyst (for example, platinum or the like) that contributes to the progress of the electrolysis reaction represented by the above formulas 1 and 2 in a potential environment where the electrolysis reaction of water can occur. It means a catalyst that is more likely to cause electrolysis of water than “ordinary catalyst”. When the normal catalyst is platinum, specific examples of the water electrolysis catalyst include Ir-based materials such as Ir and IrO ₂ , Ru-based materials such as RuO ₂ , and composites thereof. Furthermore, the “proton conductive material” is a proton conductive performance better than the porous carbon material forming the first separator, corrosion resistance that can withstand the operating environment of the fuel cell, and is fixed in the first separator. It means a material having the fixability to be obtained and the electron conductivity, and is not particularly limited as long as it has these properties. Specific examples of the proton conductive material according to the present invention include polyaniline sulfate, polyaniline phosphate, polyaniline acetate, etc. in which acidic groups such as sulfate, phosphate, acetate are introduced into polyaniline, sulfate, phosphate, Examples include polypyrrole sulfate, polypyrrole phosphate, polypyrrole acetate, etc. introduced with acidic groups such as acetic acid group, polyacenes sulfate, polyacene sulfate, polyacene acetate, etc. introduced acidic groups such as sulfuric acid group, phosphoric acid group, acetic acid group into polyacene. be able to. Furthermore, “the proton separator is provided in the first separator” means that protons and electrons generated on the water electrocatalyst can be supplied to the anode in a form capable of being supplied to the anode. Means that

  According to a second aspect of the present invention, in the fuel cell according to the first aspect, the proton conductive material is polyaniline sulfate.

  According to the first aspect of the present invention, the first separator including the proton conductive material and formed of the porous carbon material is provided with the heat medium flow path through which the heat medium containing at least water can flow, A water electrolysis catalyst is provided on the surface of the heat medium flow path. Therefore, water contained in the heat medium flowing in the heat medium flow path can be decomposed on the water electrocatalyst to generate protons and electrons, and the protons and electrons thus generated can be converted into proton conductive materials. Can lead to the anode. Therefore, even if the anode is exposed to a high potential state due to the lack of fuel, protons and electrons are supplied from the first separator, so that deterioration of the constituent material of the anode can be suppressed. That is, according to the first aspect of the present invention, it is possible to provide a fuel cell capable of suppressing material deterioration at the time of fuel shortage.

  According to the second aspect of the present invention, polyaniline sulfate is provided as the proton conductive material. Since polyaniline sulfate has a sulfate group, it has good proton conductivity. Therefore, according to the second aspect of the present invention, in addition to the above effects, a fuel cell capable of reducing resistance overvoltage caused by proton conduction can be provided.

When the fuel cell is operated in a fuel-deficient state in which the hydrogen supplied to the anode is insufficient, the anode is exposed to a high potential state. Then, in the anode exposed to the high potential state, the following reaction occurs because protons and electrons consumed in the reaction of Formula 2 are supplied.
H ₂ O → (1/2) O ₂ + 2H ⁺ + 2e ⁻ (Formula 3)
Here, Formula 3 is an electrolysis reaction of water, and while water is present on the anode side, protons and electrons are generated by the reaction. However, if the reaction of the above formula 3 does not occur in the anode exposed to a high potential state due to depletion of water on the anode side, in the fuel cell provided with carbon as a constituent material of the anode, Protons and electrons are generated.
(1 / 2C) + H ₂ O → (1/2) CO ₂ + 2H ⁺ + 2e ⁻ (Formula 4)
The above equation 4 is an oxidation reaction of carbon, and as the reaction proceeds, carbon carrying the catalyst, carbon contained in the diffusion layer, and the like deteriorate. Therefore, in order to suppress the material deterioration of the anode, it is necessary to suppress the reaction of the above formula 4. It is important to supply water decomposed by the above formula 3 to the anode side when the fuel is insufficient. is there. And in order to produce the reaction of the said Formula 3, it is preferable to set it as the fuel cell of the form with which a water electrolysis catalyst is provided in the anode side.

  The present invention has been made from such a viewpoint, and the gist thereof is that water can be easily supplied to the water electrocatalyst provided on the anode side, and protons and electrons generated on the water electrocatalyst can be easily supplied to the anode. Therefore, it is an object of the present invention to provide a fuel cell capable of improving power generation performance by suppressing material deterioration when fuel is scarce.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In the following drawings, the description of the sealing means provided to ensure the sealing performance of the reaction gas and the heat medium is omitted unless otherwise specified, but the sealing performance of the fuel cell of the present invention is the predetermined sealing means. (For example, a fluororubber gasket or the like disposed at the end of a single cell).

1. First Embodiment FIG. 1 is a cross-sectional view schematically showing a partial configuration example of a single cell (hereinafter simply referred to as “fuel cell”) provided in a fuel cell of the present invention according to a first embodiment. The horizontal direction in the figure is the cell stacking direction.

  As shown, the fuel cell 100 of the present invention according to the first embodiment includes an electrolyte membrane 1, an anode catalyst layer 2a disposed on one side thereof, and a cathode catalyst layer 3a disposed on the other side. An anode diffusion layer 2b disposed on one side of the MEA 5, a cathode diffusion layer 3b disposed on the other side, and a first separator disposed outside the anode diffusion layer 2b. 6 and a second separator 7 disposed outside the cathode diffusion layer 3b. The anode 2 includes an anode catalyst layer 2a and an anode diffusion layer 2b, and the cathode 3 includes a cathode catalyst layer 3a and a cathode diffusion layer 3b. Further, the first separator 6 is made of porous carbon, and the first separator 6 includes first reaction gas channels 8a, 8a,... And heat medium channels 9a, 9a,. The first separator 6 is provided with polyaniline sulfate 11, 11,..., And the surface of the heat medium flow passages 9a, 9a,. ing. Further, the second separator 7 is provided with second reaction gas channels 8b, 8b,... And heat medium channels 9b, 9b,. In the fuel cell 100 of the above embodiment, the hydrogen-containing gas (hereinafter referred to as “hydrogen”) humidified in the first reaction gas channels 8a, 8a,... Is converted into the second reaction gas channels 8b, 8b,. Are supplied with oxygen-containing gas (hereinafter referred to as “air”), and cold water is supplied to the first heat medium passages 9a, 9a,... And the second heat medium passages 9b, 9b,. Alternatively, it is operated in a state in which a heat medium such as warm water (hereinafter referred to as “water”) flows.

  The hydrogen supplied through the first reaction gas flow paths 8a, 8a,... Passes through an anode diffusion layer 2b made of carbon paper or the like, and is usually a catalyst (for example, platinum-supported carbon; the same applies hereinafter) and an electrolyte component (for example, Nafion, etc. Nafion is a registered trademark of DuPont, USA, and the same applies hereinafter.), And is usually decomposed into protons and electrons on the catalyst (Formula 1 above). The protons thus generated pass through the electrolyte membrane 1 including the electrolyte component, and reach the cathode catalyst layer 3a including the normal catalyst and the electrolyte component. In contrast, since electrons cannot pass through the electrolyte membrane 1, they reach the cathode catalyst layer 3a via an external circuit. On the other hand, the air supplied through the second reaction gas flow paths 8b, 8b,... Reaches the cathode catalyst layer 3a through the cathode diffusion layer 3b made of carbon paper or the like. Then, on the normal catalyst provided in the cathode catalyst layer 3a, oxygen reacts with protons and electrons that have moved from the anode catalyst layer 2a to generate water (formula 2). While a sufficient amount of reaction gas is supplied to the anode catalyst layer 2a and the cathode catalyst layer 3a, water is generated by the reaction of the above formulas 1 and 2, and electric energy can be taken out.

  By the way, the PEFC is usually used in a stack form in which a large number of cells are stacked, and electric energy is extracted from the PEFC in the stack form. For this reason, even if some cells provided in the stack are incapable of generating power due to lack of fuel due to insufficient hydrogen supply, etc., if other cells are operating normally, the stack will not be able to generate electrical energy. It can be taken out. As described above, when electric energy is taken out from the stack including the non-power generation cell, the anode is exposed to a high potential state in the non-power generation cell, and the reactions of the above formulas 3 and 4 occur. When the water on the anode side is depleted, the reaction of the above formula 4 proceeds, and the anode material is deteriorated.

  On the other hand, humidified hydrogen is supplied to the first reaction gas flow paths 8a, 8a,..., And water is generated by the above equation 2 when the fuel cell is operated. Here, during the normal operation of the fuel cell 10, a sufficient amount of hydrogen is supplied to the first reaction gas channels 8a, 8a,..., So that excess water present in the anode 2 is removed from the first reaction gas channel 8a. , 8a, can be discharged out of the cell together with hydrogen flowing inside. However, when the supply of hydrogen to the anode 2 is interrupted (hereinafter referred to as “hydrogen deficient state”), the water discharge efficiency decreases, so that water is contained in many pores provided in the first separator 6. It is thought to stay.

  As illustrated, the fuel cell 100 of the present invention includes polyaniline sulfates 11, 11,... In the first separator 6, and the first heat medium flow paths 9 a, 9 a,. Are provided with water electrocatalysts 10, 10,. In addition, the polyaniline sulfates 11, 11,... Are provided in a form that connects the water electrocatalysts 10, 10,... And the anode diffusion layer 2b. Therefore, according to the fuel cell 100, even if the anode 2 is in a hydrogen deficient state and the anode 2 is exposed to a high potential state, in addition to the water retained in the first separator 6, the first heat medium flow paths 9a, 9a ,... Can be easily supplied to the water electrocatalysts 10, 10,..., So that water decomposed on the water electrocatalysts 10, 10,. Then, protons and electrons generated by this reaction are guided to the anode 2 through the polyaniline sulfates 11, 11,. Therefore, according to the fuel cell 100, protons and electrons can be supplied from the first separator 6 to the anode 2, so that the reaction of the above formula 4 can be suppressed and the material deterioration of the anode 2 can be suppressed. That is, according to the fuel cell 100 according to the first embodiment, material deterioration at the time of fuel shortage can be suppressed.

  Here, as a method for arranging the polyaniline sulfate provided in the first separator according to the present invention, for example, the first heat medium flow path and the first reaction gas flow path are formed in the first separator formed in a plate shape. Thereafter, a method of forming a through hole from the surface of the first heat medium flow channel to the surface side on which the first reaction gas flow channel is formed, filling the through hole with polyaniline sulfate, and the like can be exemplified. . In addition, the polyaniline sulfate may be disposed and fixed in a reduced pressure environment by a method such as infiltrating the polyaniline sulfate into the first separator in which the first heat medium flow path and the first reaction gas flow path are formed. good.

  Moreover, as a method for arranging the water electrocatalyst provided in the first separator according to the present invention, for example, after forming the first heat medium channel in the porous carbon, water is applied to the surface of the first heat medium channel. The method of immobilizing an electrocatalyst can be mentioned.

2. Second Embodiment FIG. 2 is a cross-sectional view schematically showing a partial configuration example of a fuel cell of the present invention according to a second embodiment, and the horizontal direction in the figure is the cell stacking direction. 2, those having the same configuration as the members and substances shown in FIG. 1 are denoted by the same reference numerals used in FIG. 1, and the description thereof is omitted as appropriate.

  As shown in FIG. 2, the fuel cell 200 of the present invention according to the second embodiment includes an MEA 5, an anode diffusion layer 2b disposed on one side of the MEA 5, and a cathode diffusion layer disposed on the other side. 3b, a first separator 26 disposed outside the anode diffusion layer 2b, and a second separator 7 disposed outside the cathode diffusion layer 3b. The first separator 26 is formed of porous carbon and includes first reaction gas channels 8a, 8a,... And first heat medium channels 9a, 9a,. , 9a,... Are provided with water electrocatalysts 10, 10,. Further, the first separator 26 is provided with the reverse osmosis membrane 22, and the polyaniline sulfate 11, 11,. In the fuel cell 200, a heat medium such as LLC (hereinafter referred to as “LLC”) is formed in the flow path (not shown in FIG. 2) located on the opposite side of the first heat medium flow path 9a, 9a,. , “LLC”) flows, and pure water that has permeated through the reverse osmosis membrane 22 (hereinafter simply referred to as “water”) moves to the first heat medium flow paths 9a, 9a,. , Are supplied to water electrocatalysts 10, 10,.

  As shown in FIG. 2, the fuel cell 200 of the present invention includes a reverse osmosis membrane 22. Therefore, even if a heat medium other than water is used, only water that has permeated through the reverse osmosis membrane 22 can be supplied onto the water electrocatalysts 10, 10,. Therefore, according to the second embodiment, even when a heat medium other than water is used, protons and electrons can be supplied to the anode. Therefore, a fuel cell that can suppress material deterioration at the time of fuel shortage is provided. Can be provided.

  Here, as a method of arranging the reverse osmosis membrane 22 provided in the first separator 26 according to the second embodiment, for example, the first heat medium flow paths 9a, 9a,... And the first reaction gas flow paths 8a, 8a are used. ,... Are formed in the first separator 26 where the reverse osmosis membrane 22 is disposed, and the through hole is filled with a dissolved or molten reverse osmosis membrane and fixed. be able to. Further, the end portion can be sealed with a sealing member without providing a through hole.

  In the said embodiment, although the form with which polyaniline sulfate is provided as a proton-conductive material was illustrated, the proton-conductive material with which the fuel cell of this invention is provided is not limited to this. Other proton conductive materials may be provided as long as protons and electrons generated on the water electrocatalyst can be supplied to the anode in the operating environment of the fuel cell. Specific examples of proton conductive materials that can be provided in the fuel cell of the present invention include polyaniline sulfate, polyaniline phosphate, polyaniline acetate, polypyrrole sulfate, polypyrrole phosphate, polypyrrole acetate, polyacene sulfate, polyacene phosphate, polyacene acetate, and the like. Can be mentioned. However, from the viewpoint of enabling the performance of the fuel cell to be improved by reducing the resistance overvoltage, it is preferable to use a proton conductive material (for example, polyaniline sulfate) having good proton conductivity and electronic conductivity. .

Moreover, in the said embodiment, although the form with which Ir is provided as a water electrolysis catalyst was illustrated, the water electrolysis catalyst with which the fuel cell of this invention can be equipped is not limited to Ir. The water electrocatalyst according to the present invention only needs to be a catalyst that causes an electrolysis reaction of water more easily than a normal catalyst. Specific examples of the water electrocatalyst include Ir, Ir-based materials such as IrO ₂ , Examples thereof include Ru-based materials such as RuO ₂ and composites thereof.

  Furthermore, in the said embodiment, although the form with which the surface of the 1st heat-medium flow path 9a, 9a, ... was equipped with the water electrolysis catalyst 10, 10, ... was illustrated, in the fuel cell of this invention, it is equipped with a 1st separator. The place where the water electrolysis catalyst to be disposed can be disposed is not limited to the surface of the first heat medium flow path. In addition to the above form, for example, a form in which a water electrolysis catalyst is provided on the surface of the first heat medium flow path and the inside of the first separator may be employed.

  In the above embodiment, the anode catalyst layer 2a having the normal catalyst and the electrolyte component is exemplified. However, in the fuel cell of the present invention, the anode catalyst layer having the normal catalyst, the electrolyte component, and the water electrolysis catalyst is provided. It is also good. With such a form, the frequency of water electrolysis reaction can be improved. Therefore, even in such a form, it is possible to provide a fuel cell capable of easily suppressing material deterioration when the anode is exposed to a high potential state and improving power generation performance.

  Furthermore, although the fuel cells 100 and 200 in the form in which the anode 2 and the cathode 3 are provided with the diffusion layers 2b and 3b have been exemplified so far, the fuel cell of the present invention is not limited to the form in which the diffusion layer is provided. In the fuel cell of the present invention, the anode and the cathode may be provided with at least a catalyst layer (anode catalyst layer and cathode catalyst layer).

It is sectional drawing which shows roughly the example of a partial structure of the fuel cell of this invention concerning 1st Embodiment. It is sectional drawing which shows roughly the example of a partial structure of the fuel cell of this invention concerning 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrolyte membrane 2 Anode 2a Anode catalyst layer 2b Anode diffusion layer 3 Cathode 3a Cathode catalyst layer 3b Cathode diffusion layer 5 MEA
6, 26 First separator 7 Second separator 8a First reaction gas flow path 8b Second reaction gas flow path 9a First heat medium flow path 9b Second heat medium flow path 10 Water electrocatalyst 11 Polyaniline sulfate (proton conductive material) )
22 Reverse osmosis membrane 100, 200 Fuel cell

Claims (2)

MEA including an anode and a cathode, and an electrolyte membrane disposed between the anode and the cathode, a first separator disposed on the anode side, and a second separator disposed on the cathode side And comprising
The first separator is formed of a porous carbon material, and the first separator is provided with a heat medium flow path through which a heat medium containing at least water can flow.
At least a water electrocatalyst is disposed on the surface of the heat medium flow path,
A fuel cell, wherein a proton conductive material is provided in the first separator. The fuel cell according to claim 1, wherein the proton conductive material is polyaniline sulfate.

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