JP5034344B2 - Gas diffusion electrode and fuel cell using the same - Google Patents

Description

  The present invention relates to a gas diffusion electrode, particularly a gas diffusion electrode for a fuel cell and a fuel cell using the same. More specifically, the present invention relates to a gas diffusion electrode, particularly a fuel cell gas diffusion electrode capable of suppressing deterioration of an electrocatalyst due to carbon corrosion and flooding phenomenon in a catalyst layer under a high current density condition. The present invention relates to a fuel cell used.

  In recent years, in response to social demands and trends against the background of energy and environmental problems, fuel cells that can operate at room temperature and obtain high output density have attracted attention as power sources for electric vehicles and stationary power sources. A fuel cell is a clean power generation system in which the product of an electrode reaction is water in principle and has almost no adverse effect on the global environment. In particular, the polymer electrolyte fuel cell is expected as a power source for electric vehicles because it operates at a relatively low temperature. The polymer electrolyte fuel cell has a structure in which an electrolyte membrane is sandwiched between gas diffusion electrodes comprising a catalyst layer and a gas diffusion layer in contact with the membrane (in this specification, this structure is referred to as an “electrolyte membrane-electrode assembly” or In general, a separator is further sandwiched outside the electrolyte membrane-electrode assembly.

In a fuel cell, electricity can be taken out through the following electrochemical reaction or the like. First, hydrogen contained in the fuel gas supplied to the anode (fuel electrode) side is oxidized by the catalyst particles to become protons and electrons (H ₂ → 2H ⁺ + 2e ⁻ ). Next, the produced protons pass through the polymer electrolyte contained in the fuel electrode side electrode catalyst layer and the polymer electrolyte membrane in contact with the electrode catalyst layer, and reach the cathode (oxygen electrode) side electrode catalyst layer. In addition, the electrons generated in the fuel electrode-side electrode catalyst layer include the conductive material constituting the electrode catalyst layer, the gas diffusion layer in contact with the polymer electrolyte membrane on the electrode catalyst layer, the separator, and the outside. The oxygen electrode side electrode catalyst layer is reached through the circuit. The protons and electrons that reach the oxygen electrode side electrode catalyst layer react with oxygen contained in the oxidant gas supplied to the oxygen electrode side to generate water (4H ⁺ + 4e ⁻ + 1 / 2O ₂ → H ₂ O ). Such an electrochemical reaction mainly proceeds at a three-phase interface where catalyst particles, a polymer electrolyte, and a reaction gas such as a fuel gas or an oxidant gas are in contact with each other. Therefore, the gas diffusion layer is required to uniformly supply the supplied reaction gas to the electrode.

Such a fuel cell may be placed in a voltage reversal state where the polarity of the cell is forced to be reversed. If an electrochemical reaction occurs during voltage reversal, electrolysis of water generated at the anode and oxidation (corrosion) of the anode components occur. In order to solve such problems, an anode including a catalyst composition for generating oxygen from water in addition to a catalyst composition for oxidizing an original fuel gas has been proposed (Patent Document 1). reference).
Special table 2003-508877 gazette

  Since the polymer electrolyte membrane in a fuel cell usually does not show high proton conductivity unless it is wet, the reaction gas supplied to the solid polymer fuel cell is humidified using a gas humidifier or the like, It is necessary to make the humidity distribution of the solid polymer electrolyte membrane uniform. In particular, under operating conditions such as high humidification and high current density, the amount of water that moves with protons that move through the solid polymer electrolyte membrane from the anode to the cathode, and the amount of water that is generated in the cathode-side electrode catalyst layer The amount of product water that agglomerates increases. At this time, since the generated water stays in the catalyst layer, particularly the cathode-side electrode catalyst layer, it causes a flooding phenomenon that closes the pores used as the reaction gas supply path. In the fuel cell having the anode described in Patent Document 1, only the problem on the anode side is targeted. The flooding phenomenon on the cathode side and the problem of carbon corrosion as described in detail below are described in Patent Document 1. It was not clear at the time of filing. For this reason, Patent Document 1 aims to suppress electrolysis of water generated in the anode and oxidation (corrosion) of the components of the anode, and does not consider the cathode at all. Therefore, in the fuel cell having the anode described in Patent Document 1, the hydrophilicity of the cathode catalyst layer is increased during normal operation, causing the above-described flooding phenomenon. For this reason, when the fuel cell having the anode described in Patent Document 1 is used, the diffusion of the reaction gas is hindered, the electrochemical reaction is hindered, and as a result, there is a high possibility that the battery performance is lowered. There's a problem.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a gas diffusion electrode capable of preventing the flooding phenomenon of the catalyst layer during normal operation.

  Another object of the present invention is to provide a gas diffusion capable of suppressing and preventing the corrosion of carbon in the catalyst layer, particularly the electrode catalyst layer on the cathode side, and the flooding phenomenon of the catalyst layer, particularly the cathode catalyst layer, during normal operation. It is to provide an electrode.

As a result of diligent research to solve the above problems, the present inventor has paid attention to the problem of thinning of the catalyst layer due to corrosion of the carbon support in the cathode catalyst layer described in detail below. That is, for example, when the operation of the fuel cell is stopped and left for several hours or more, an anode catalyst layer system or a cathode catalyst layer is caused by a small amount of leak from a seal portion around the stack or a leak from a pump or a compressor connected to the stack. Since the outside air (air) is mixed into the system and the hydrogen remaining on the anode catalyst layer side is consumed by oxygen in the outside air, the anode catalyst layer-cathode catalyst layer system eventually has an air-air gas atmosphere. It has become. When hydrogen is introduced into the anode side after starting in such a state, a local battery is formed from upstream (hydrogen supply side) to downstream (air atmosphere) of the anode. Here, since the cathode in the region facing the air existing part downstream of the anode becomes a high potential (about 1.5 V) with respect to the electrolyte potential, a large difference between the cathode potential and the electrolyte potential becomes a driving force. In this region, a reaction of C + 2H ₂ O → CO ₂ + 4H ⁺ + 4e ⁻ occurs with respect to the carbon carrier which is an electron conductive material in the cathode catalyst layer, the carbon is corroded, and the pore structure of the catalyst layer is broken. It is considered that the catalyst layer is thinned, whereby the gas diffusibility and drainage of the catalyst layer are lowered, the concentration overvoltage is increased, and the battery characteristics are lowered. As described above, such a phenomenon occurs in the cathode catalyst layer region facing the upstream side of the anode where hydrogen is present, and also in the cathode catalyst layer during normal power generation, although at a very slow speed. When starting after standing for a relatively long period of time, the difference between the cathode potential, which is the driving force for corrosion, and the electrolyte potential is particularly large in the cathode catalyst layer region in the region facing the air existing portion downstream of the anode. The corrosion reaction rate is increased, and the catalytic activity is decreased and the catalyst layer is thinned in this region. In addition, moisture generated by electrochemical reaction and moisture contained in the gas supplied through the gas flow path provided in the separator are likely to stay in the catalyst layer, and in the catalyst layer, from the inlet side to the outlet side of the gas flow path. However, since the corrosion of the carbon support proceeds using water as an oxidant as is apparent from the above reaction formula, the corrosion of the carbon support, which causes a decrease in the durability of the fuel cell, As the starting / stopping / continuous operation is repeated, the gas flow path is remarkably generated from the inlet side to the outlet side, and accordingly, the thickness of the cathode catalyst layer on the outlet side of the gas flow path is particularly reduced. Variations occur. Thus, even if there is little corrosion of the carbon carrier on the inlet side of the gas flow path in the catalyst layer, the smoothness of the catalyst layer is impaired due to the great corrosion of the carbon carrier on the outlet side, and the battery sealing performance It is considered that the power generation performance of the entire battery is lowered due to the decrease in the battery.

  For this reason, in order to solve the problems described in the background art and the above problems, the present inventor has conducted extensive research on a gas diffusion electrode comprising a gas diffusion layer and a catalyst layer. It has been found that when it is arranged at the interface between the diffusion layer and the catalyst layer, a water electrolysis reaction by catalysis proceeds at this interface, whereby moisture generated in the catalyst layer moves to the gas diffusion layer side by diffusion. Such movement of moisture from the catalyst layer to the gas diffusion layer prevents or prevents water from staying in the catalyst layer, particularly the cathode-side electrode catalyst layer. It was also found that the flooding phenomenon that clogs the pores that were the reaction gas supply path can be effectively suppressed / prevented. In addition to the above knowledge, the present inventor can arrange the catalyst having water electrolysis activity at the interface between the gas diffusion layer and the catalyst layer as described above, thereby improving the efficiency without retaining the water generated in the catalyst layer. Since it can be discharged well, the flooding phenomenon does not occur or does not occur without clogging the pores that were the reaction gas supply path in the catalyst layer (especially cathode side electrode catalyst layer), especially under high current density. I also found it difficult. Based on the above findings, the present invention has been completed.

  That is, the above object is achieved by a gas diffusion electrode comprising a gas diffusion layer and a catalyst layer, wherein a catalyst having water electrolysis activity is disposed at the interface between the gas diffusion layer and the catalyst layer.

  According to the gas diffusion electrode of the present invention, it is possible to suppress / prevent deterioration of the electrode catalyst due to carbon corrosion, and to suppress / prevent flooding phenomenon in the catalyst layer at a high current density, particularly in the cathode side electrode catalyst layer. .

  Embodiments of the present invention will be described below.

The first of the present invention relates to a gas diffusion electrode comprising a gas diffusion layer and a catalyst layer, wherein the catalyst having water electrolysis activity is disposed at the interface between the gas diffusion layer and the catalyst layer. . The present invention is characterized in that a catalyst having water electrolysis activity is disposed at the interface between the gas diffusion layer and the catalyst layer. By adopting such a structure, water electrolysis is performed near the interface between the catalyst layer and the gas diffusion layer, and the water electrolysis reaction proceeds by the action of the catalyst having water electrolysis activity near the interface. Thus, moisture generated in the catalyst layer moves to the gas diffusion layer side by diffusion. Due to such movement of water, the retention of water in the catalyst layer, particularly the cathode-side electrode catalyst layer, which has been a problem in the past, does not occur or hardly occurs. Therefore, it is possible to effectively suppress and prevent the flooding phenomenon that clogs the pores that have become the reaction gas supply path in the catalyst layer, particularly the cathode side electrode catalyst layer, particularly the flooding phenomenon at a high current density. Furthermore, according to the present invention, since water generated in the catalyst layer can be smoothly discharged from the catalyst layer, the reaction of C + 2H ₂ O → CO ₂ + 4H ⁺ + 4e ^{− to} the electron conductive material (carbon support) in the cathode catalyst layer is performed. It can be effectively prevented. Therefore, the gas diffusion electrode of the present invention can effectively suppress and prevent carbon corrosion, particularly corrosion of carbon in the electrode catalyst layer on the cathode side. In addition to the above advantages, in the present invention, since a catalyst having water electrolysis activity is disposed in the vicinity of the interface between the catalyst layer and the gas diffusion layer that is most effective for discharging generated water from the catalyst layer, a small amount of water electrolysis is achieved. A flooding phenomenon and carbon corrosion can be suppressed / prevented with an active catalyst amount.

  In the present invention, the arrangement form of the catalyst having water electrolysis activity is located at the interface between the gas diffusion layer and the catalyst layer and can attract water from the catalyst layer by the water electrolysis reaction in the vicinity of the interface. There is no particular limitation. Specifically, (a) a mode in which a layer having a catalyst having water electrolysis activity is inserted between the gas diffusion layer and the catalyst layer; (a) a mode in which a catalyst having water electrolysis activity is disposed in the gas diffusion layer Etc. are preferred. In the present invention, the catalyst layer does not substantially contain a catalyst having water electrolysis activity.

  In the form (a), a layer having a catalyst having water electrolysis activity is newly provided between the gas diffusion layer and the catalyst layer. By taking this form, it is easy to adjust the amount of the catalyst having water electrolysis activity in the layer, and therefore, it is possible to easily achieve the flooding phenomenon and the effect of suppressing and preventing carbon corrosion to the desired level. it can. In the embodiment (a), the layer having a catalyst having water electrolysis activity is inserted into the above-mentioned layer over the entire interface between the gas diffusion layer and the catalyst layer, or the gas corresponding to the gas outlet portion where the product water is likely to accumulate. It may be inserted between the above-mentioned layers at a part of the interface between the gas diffusion layer and the catalyst layer, such as at the interface part between the diffusion layer and the catalyst layer. It is preferable that a layer having a catalyst having water electrolysis activity is disposed at least in the place where the above is performed. In the latter case, the catalyst having the water electrolysis activity can be obtained even if a layer having a relatively large area is inserted between the gas diffusion layer and the catalyst layer singly or plurally, or the gas is formed in a spot shape having a relatively small area. A plurality may be inserted between the diffusion layer and the catalyst layer.

  Further, the catalyst having water electrolysis activity may be the same or different amount of the catalyst having water electrolysis activity arranged in the layer. In the latter case, it is preferable that a large amount of the catalyst having water electrolysis activity is disposed in the layer on the side in contact with the catalyst layer and / or in the vicinity of the gas outlet, particularly on the side in contact with the catalyst layer. Since the vicinity of the gas outlet is a portion where product water tends to accumulate, by arranging a large amount of a catalyst having water electrolysis activity in such a place, the generated water is efficiently subjected to a water electrolysis reaction, and from the catalyst layer. This is because water can be attracted and retention of water generated in the catalyst layer can be suppressed / prevented. At this time, the catalyst having water electrolysis activity may be disposed only in the vicinity of the gas outlet portion with respect to the plane direction of the layer, or may be disposed so that the blending amount gradually increases from the gas inlet portion to the vicinity of the gas outlet portion. Either is acceptable. In addition, by disposing many catalysts having water electrolysis activity on the side in contact with the catalyst layer, the water generated in the catalyst layer can be efficiently used for the water electrolysis reaction, and the water concentration from the catalyst layer to the gas diffusion layer By the gradient, the generated water can be favorably moved to the gas diffusion layer with less moisture. At this time, the catalyst having water electrolysis activity is arranged in the layer so that the blending amount gradually increases from the gas diffusion layer side to the catalyst layer side, or is arranged at a predetermined thickness in a portion in contact with the catalyst layer. Or either.

  The amount of the catalyst having water electrolysis activity disposed in the layer is not particularly limited as long as it is an amount capable of satisfactorily suppressing / preventing retention of water generated in the catalyst layer. It differs depending on the arrangement form. For example, when the catalyst having water electrolysis activity is arranged in the same amount in the layer, it is preferably 5 to 50% by mass, more preferably based on the total mass (in terms of solid content) of the components constituting the layer. It is 10-30 mass%. In addition, when the catalyst having water electrolysis activity is arranged in the layer from the gas diffusion layer side to the catalyst layer side or from the gas inlet part to the gas outlet part, the catalyst is in contact with the catalyst layer. The blending amount on the side to be used is preferably 10 to 50% by mass, more preferably 20 to 40% by mass with respect to the total mass (solid content conversion) of the components constituting the layer, and the side in contact with the gas diffusion layer The concentration gradient is preferably 5 to 20% by mass, more preferably 5 to 15% by mass with respect to the total mass (in terms of solid content) of the components constituting the layer. At this time, the concentration gradient may be continuous or stepwise.

  In the form (a), the layer having a catalyst having water electrolysis activity preferably further contains electron conductive particles. Thereby, the electronic conductivity of the layer having the catalyst having water electrolysis activity is increased, and the deterioration of the cell performance accompanying the increase of the insulation resistance (IR) can be significantly suppressed / prevented. The electron conductive particles that can be used in this case are not particularly limited as long as they have electron conductivity. For example, carbon black, acetylene black, activated carbon, graphite, expanded graphite, oil furnace black, channel black, lamp black, thermal Examples thereof include carbon particles such as black. Among these, carbon black, acetylene black, and activated carbon are preferable because of excellent electron conductivity and a large specific surface area. A commercially available product may be used as the electron conductive particles. In such a case, Vulcan XC-72, Vulcan XC-72R, Vulcan P, Black Pearls 880, Black Pearls 1100, Black Pearls 1300, manufactured by Cabot Corporation may be used. Oil furnace black such as Black Pearls 2000, Regal 400, Ketjen Black EC manufactured by Lion, and # 3150 and # 3250 manufactured by Mitsubishi Chemical Co., and acetylene black such as Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd. can be used. In addition to carbon black, artificial graphite or carbon obtained from organic compounds such as natural graphite, pitch, coke, polyacrylonitrile, phenol resin, furan resin, etc. can also be used. The electron conductive particles may be used alone or in the form of a mixture of two or more. Further, the particle diameter of the electron conductive particles is not particularly limited, but considering the drainage property and the contact property with the electrode catalyst layer, the particle size is preferably 10 to 100 nm, more preferably about 30 to 70 nm.

  In addition, the amount of the electron conductive particles disposed in the layer is not particularly limited as long as it does not prevent the catalyst having water electrolysis activity from suppressing and preventing the retention of water generated in the catalyst layer. It varies depending on the type of electron conductive particles. For example, the blending amount of the electron conductive particles is preferably 5 to 80% by mass, more preferably 10 to 75% by mass with respect to the catalyst having water electrolysis activity.

  In the form (a), a layer having a catalyst having water electrolysis activity is newly provided between the gas diffusion layer and the catalyst layer. The method for forming the layer having a catalyst having water electrolysis activity is not particularly limited, and a known method can be applied in the same manner or with modification. Hereinafter, although a preferable method is described, this invention is not limited to the said method. For example, an appropriate amount of a catalyst having water electrolysis activity, electron conductive particles, and a solvent is mixed and dispersed to form a slurry (solution), and this slurry (solution) is applied onto a substrate for a gas diffusion layer and then dried. Let Then, it is preferable to heat-process at 250-400 degreeC using a muffle furnace or a baking furnace, More preferably, about 300-400 degreeC. At this time, the addition amount of the catalyst having water electrolysis activity and the electron conductive particles is as described above. The solvent is not particularly limited, and can be appropriately selected according to the type of the catalyst having water electrolysis activity and the electron conductive particles. For example, alcohol solvents such as water, perfluorobenzene, dichloropentafluoropropane, methanol and ethanol can be used. The catalyst having electrolysis activity and the electron conductive particles may be used as they are or in the form of a solution. The solvent used in the latter case is not particularly limited, and for example, the solvents described above can be used. Also, instead of applying the slurry (solution) on the gas diffusion layer substrate and drying, the slurry (solution) is once dried and pulverized to form a powder, which is then applied onto the gas diffusion layer substrate. A coating method or the like may be used. The slurry may further include a water repellent. As a result, the water repellency can be further increased to prevent the flooding phenomenon. At this time, the water repellent is not particularly limited, but fluorine such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Polymer materials such as polypropylene, polypropylene, and polyethylene. Although the addition amount of a water repellent is not specifically limited, For example, it is about 20-80 mass% with respect to the total mass (solid content conversion) of the component which comprises a layer. In particular, when the water repellent is a fluorine-based polymer material, the content of the polymer containing fluorine atoms in the layer having a catalyst having water electrolysis activity is 1 with respect to the mass 1 of the electron conductive particles. 0.1 to 2.0, more preferably 0.2 to 1.8, and still more preferably 0.3 to 1.5. The layer having a catalyst having water electrolysis activity is preferably 0.1 or more from the viewpoint of water repellency, and preferably 2.0 or less from the viewpoint of conductivity.

Alternatively, in particular, when a catalyst having water electrolysis activity is used in combination with electron conductive particles, a catalyst having water electrolysis activity may be supported on the electron conductive particles in addition to the above method. At this time, the method for supporting the catalyst having water electrolysis activity on the electron conductive particles is not particularly limited, and a known supporting method can be used similarly or modified. For example, when iridium or ruthenium is used as a catalyst having water electrolysis activity, the catalyst particle supporting method described in detail below can be used in the same manner. In addition, when using iridium oxide or ruthenium oxide as a catalyst having water electrolysis activity, in addition to the catalyst particle loading method as described in detail below, there are a solution reduction method, a heating oxidation method, an electrodeposition method, and the like. It can be preferably used. At this time, in the solution reduction method, for example, an aqueous solution of iridium nitrate or iridium chloride is used as an iridium precursor, and a reducing agent such as ethanol, methanol, propanol, formic acid, formaldehyde, ascorbic acid, sodium thiosulfate, citric acid, or the like. An iridium precursor or iridium can be supported on the electron conductive particles by mixing a reducing agent such as an acid and the electron conductive particles, heating and stirring at about 90 ° C. for 4 hours, filtering, and drying. Furthermore, it can carry | support as iridium oxide by heat-processing between 150 degreeC-400 degreeC in oxygen-containing atmosphere. Further, the heating oxidation method is not particularly limited. For example, iridium chloride (IrCl ₄ · H ₂ O), iridium chloride (H ₂ IrCl ₆ · 6H ₂ O), and iridium resin acid are mixed with water, ethanol, An iridium precursor solution is prepared by dissolving in a solvent such as butanol. The iridium precursor solution is applied to the electron conductive particles, and this is applied to an oxygen atmosphere (for example, an oxygen partial pressure of 0.1 to 0.5). A method of heat treatment under conditions of atmospheric pressure) at a temperature of 200 to 800 ° C. for 5 to 120 minutes is preferably used. The electrodeposition method is not particularly limited. For example, a method of electrodepositing iridium oxide (IrO ₂ ) by immersing electron conductive particles in an iridium complex (for example, an aqueous solution of Na ₂ IrO ₄ ). In the above method, the method of supporting iridium oxide on the electron conductive particles as a catalyst having water electrolysis activity was described in detail, but the same applies to other catalysts having water electrolysis activity such as ruthenium oxide. The method can be used.

  The gas diffusion layer used in the form (a) can be used without particular limitation as long as it is a conventionally known one. Specifically, a sheet-like material having conductivity and porosity such as a carbon woven fabric, a paper-like paper body, a felt, and a non-woven fabric; a metal mesh, and the like can be given. More specifically, carbon cloth, carbon paper (carbon paper), carbon cloth, carbon non-woven fabric, and metal mesh can be preferably used, and carbon cloth, carbon paper (carbon paper), carbon non-woven fabric, and metal mesh are more preferable. These materials have high electronic conductivity, and can significantly suppress / prevent a decrease in cell performance accompanying an increase in insulation resistance (IR). Moreover, a commercial item can also be used for a gas diffusion layer, for example, carbon paper TGP series by Toray Industries, Inc., carbon cloth by E-TEK, etc. are mentioned.

  The gas diffusion layer preferably contains a water repellent in the base material for the purpose of further improving water repellency and preventing a flooding phenomenon. Although it does not specifically limit as said water repellent, It is fluorine-type, such as a polytetrafluoroethylene (PTFE), a polyvinylidene fluoride (PVDF), a polyhexafluoropropylene, a tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Examples thereof include polymer materials, polypropylene, and polyethylene. When a water repellent is contained in the gas diffusion layer, a general water repellent treatment method may be used. For example, after immersing the base material used for a gas diffusion layer in the dispersion liquid of a water repellent agent, the method of heat-drying with oven etc. is mentioned.

  In the form (a), the thickness of the layer having a catalyst having water electrolysis activity is not particularly limited as long as it can sufficiently suppress and prevent the flooding phenomenon. Specifically, the total thickness of the gas diffusion layer and the layer having a catalyst having water electrolysis activity is 100 to 500 μm, more preferably 200 to 500 μm, still more preferably 200 to 400 μm, and most preferably 200 to 300 μm. Preferably there is. With such a thickness, both the mechanical strength and drainage of the gas diffusion layer can be sufficiently secured. Among these, the thickness of the gas diffusion layer is preferably 199 to 400 μm, more preferably 199 to 350 μm, and most preferably 199 to 290 μm. With such a thickness, both the mechanical strength and drainage of the gas diffusion layer can be sufficiently secured. The thickness of the layer having a catalyst having water electrolysis activity is preferably 1 to 100 μm, more preferably 1 to 50 μm, and most preferably 1 to 10 μm. With such a thickness, the flooding phenomenon and the deterioration of the catalyst layer can be sufficiently suppressed and prevented.

  Next, the form of said (a) arrange | positions the catalyst which has water electrolysis activity in a gas diffusion layer. By taking this form, there is no extra layer between the catalyst layer and the gas diffusion layer, so the gas diffusion electrode can be made thin, and the gas diffusion layer side in contact with the catalyst layer Since the catalyst having water electrolysis activity can be highly dispersed, the water electrolysis reaction proceeds here, and the water produced in the catalyst layer can be discharged smoothly. Can control and prevent flooding and carbon corrosion. In the embodiment (a), the catalyst having water electrolysis activity may be disposed over the entire contact surface between the catalyst layer and the gas diffusion layer, or the catalyst layer and the gas diffusion layer corresponding to the gas outlet portion where product water is likely to accumulate. It may be arranged at a part of the interface between the gas diffusion layer and the catalyst layer, such as on the contact surface with the catalyst, but at least in a place corresponding to a portion where the generated water is likely to accumulate, such as near the gas outlet, water electrolysis It is preferable to arrange a catalyst having activity. In the latter case, the catalyst having water electrolysis activity may be a catalyst having a relatively large area or a spot having a relatively small area even if it is disposed on the contact surface between the plurality of catalyst layers and the gas diffusion layer. A plurality of them may be arranged on the contact surface between the gas diffusion layer and the gas diffusion layer.

  Furthermore, the catalyst having water electrolysis activity may be arranged in the same amount or in different amounts in the contact surface direction between the catalyst layer and the gas diffusion layer. In the latter case, the catalyst having water electrolysis activity is present on the contact surface between the catalyst layer and the gas diffusion layer on the side in contact with the catalyst layer and / or near the gas outlet, particularly on the side in contact with the catalyst layer. In particular, it is preferable to arrange many. Since the vicinity of the gas outlet is a portion where product water tends to accumulate, by arranging a large amount of a catalyst having water electrolysis activity in such a place, the generated water is efficiently subjected to a water electrolysis reaction, and water is retained. This is because it can be suppressed / prevented. At this time, the amount of the catalyst having water electrolysis activity is gradually increased from the gas inlet portion to the gas outlet portion even if it is arranged only near the gas outlet portion with respect to the contact surface direction between the catalyst layer and the gas diffusion layer. Any of these may be arranged. In addition, by arranging a large amount of a catalyst having water electrolysis activity on the contact surface between the catalyst layer and the gas diffusion layer, the water generated in the catalyst layer can be efficiently used for the water electrolysis reaction. The water concentration gradient up to is rapidly formed, and the produced water can be favorably transferred to the gas diffusion layer with less moisture. At this time, the catalyst having water electrolysis activity may be arranged so that the blending amount gradually increases from the side not contacting the catalyst layer of the gas diffusion layer toward the side contacting the catalyst layer in the thickness direction of the gas diffusion layer. Alternatively, it may be arranged at a predetermined thickness in the gas diffusion layer portion in contact with the catalyst layer. In the latter case, the catalyst having water electrolysis activity is preferably arranged in an amount of 1 to 20%, more preferably about 1 to 10% with respect to the thickness of the gas diffusion layer. If it exists in such a range, the catalyst which has water electrolysis activity can discharge | emit the water produced | generated in a catalyst layer efficiently by water electrolysis reaction.

  The amount of the catalyst having water electrolysis activity placed in the layer is not particularly limited as long as it is an amount capable of satisfactorily suppressing / preventing retention of water generated in the catalyst layer, and the type of catalyst having water electrolysis activity and gas diffusion are not limited. It varies depending on the arrangement form in the layer. For example, in the case where the catalyst having water electrolysis activity is arranged in the same amount in the gas diffusion layer, the total mass of components constituting the layer portion (in terms of solid content) in the portion having the catalyst having water electrolysis activity Preferably, it is 5-50 mass%, More preferably, it is 10-30 mass%. In addition, when the catalyst having water electrolysis activity is arranged in the layer from the gas diffusion layer side to the catalyst layer side or from the gas inlet part to the gas outlet part, the catalyst is in contact with the catalyst layer. The catalyst having water electrolysis activity is preferably 10 to 50% by mass, more preferably 20 to 40% by mass, based on the total mass (in terms of solid content) of the components constituting the layer. Among the gas diffusion layers that are arranged, the blending amount in the part farthest from the catalyst layer is preferably 1 to 20% by mass with respect to the total mass (in terms of solid content) of the components constituting the layer, More preferably, the concentration gradient can be 5 to 15% by mass. At this time, the concentration gradient may be continuous or stepwise.

  In the form (a), the gas diffusion layer may further include electron conductive particles. Thereby, the electronic conductivity of the layer having the catalyst having water electrolysis activity is further increased, and the deterioration of the cell performance accompanying the increase of the insulation resistance (IR) can be significantly suppressed / prevented. The electron conductive particles that can be used in this case are not particularly limited as long as they have electron conductivity, and the same particles as those listed in the form (a) can be used. The particle size of the electron conductive particles is not particularly limited, but considering the drainage property and the contact property with the electrode catalyst layer, it is preferably about 10 to 100 nm, more preferably about 30 to 70 nm. In addition, the amount of the electron conductive particles disposed in the layer is not particularly limited as long as it does not prevent the catalyst having water electrolysis activity from suppressing and preventing the retention of water generated in the catalyst layer. It varies depending on the type of electron conductive particles. For example, the compounding amount of the electron conductive particles is preferably 5 to 80% by mass, and more preferably 10 to 75% by mass with respect to the total mass (in terms of solid content) of the components constituting the layer.

  In the form (a), a catalyst having electrolytic activity is disposed in the gas diffusion layer. The method for disposing the catalyst having electrolytic activity in the gas diffusion layer is not particularly limited, and a known method can be applied in the same manner or with modification. Hereinafter, although a preferable method is described, this invention is not limited to the said method. For example, a catalyst having water electrolysis activity is dispersed in a solvent to form a slurry (solution). Next, after the base material used for the gas diffusion layer is immersed in this slurry (solution) to a predetermined depth, it is taken out and heated and dried in an oven or the like. At this time, the addition amount of the catalyst having water electrolysis activity is as described above and was not described in the above method, but in addition to the catalyst having water electrolysis activity, electron conductive particles may be further added, The addition amount of the electron conductive particles at this time is also the same as described above. The solvent is not particularly limited, and can be appropriately selected according to the catalyst having water electrolysis activity and, if necessary, the type of electron conductive particles. For example, alcohol solvents such as water, perfluorobenzene, dichloropentafluoropropane, methanol and ethanol can be used. In the above method, the depth of immersing the base material used in the gas diffusion layer in the slurry is not particularly limited as long as the water generated in the catalyst can be efficiently subjected to the water electrolysis reaction. Is such a depth that the catalyst having water electrolysis activity is disposed about 1 to 30 μm, more preferably about 1 to 10 μm from the side of the gas diffusion layer in contact with the catalyst layer. If the blending amount of the catalyst having water electrolysis activity as described above is not reached, the above steps may be repeated a plurality of times until the predetermined amount is reached. Further, in the above method, the immersion conditions are not particularly limited as long as the catalyst having a desired water electrolysis activity can be disposed in the gas diffusion layer. Usually, the gas diffusion is performed at 60 to 120 ° C. for about 10 to 180 minutes. It is preferable to immerse the substrate used for the layer in the slurry. The slurry may further include a water repellent. Thereby, since high water repellency is provided to the gas diffusion layer, flooding phenomenon and the like can be more effectively prevented. At this time, the water repellent is not particularly limited, and those similar to those listed in the form (a) can be used, and the amount of the water repellent added is not particularly limited. Is about 5 to 80% by mass with respect to the total mass (in terms of solid content) of the components constituting the.

  Alternatively, the catalyst having electrolysis activity may be disposed in the gas diffusion layer by applying a slurry (solution) in which a catalyst having water electrolysis activity is dispersed in a solvent to the base material used for the gas diffusion layer. . At this time, the method for applying the slurry onto the base material used for the gas diffusion layer is not particularly limited, and a known method such as a screen printing method, a deposition method, or a spray method can be similarly applied. Unless otherwise specified, the application part, the solvent, and the like in such a method are the same as those described above.

Or, in particular, when a catalyst having water electrolysis activity is used in combination with electron conductive particles, a catalyst having water electrolysis activity is supported on the electron conductive particles in the gas diffusion layer as described above. Things may be arranged. This can be achieved by a method similar to that described above. For example, an aqueous solution of iridium nitrate or iridium chloride is used as an iridium precursor, and a reducing agent such as ethanol, methanol, propanol, formic acid, formaldehyde, ascorbic acid, sodium thiosulfate, citric acid, or the like is used. The liquid particles are mixed to prepare a mixed solution, and the base material used for the gas diffusion layer is immersed in the mixed solution at the temperature and time as described above, then taken out and heated at about 90 ° C. for 4 hours and dried. Thus, it is possible to use a solution reduction method in which iridium supported at least partially on the electron conductive particles is disposed in the gas diffusion layer. At this time, by carrying out heat treatment between 150 ° C. and 400 ° C. in an oxygen-containing atmosphere, it is possible to dispose iridium oxide supported in the form of electron conductive particles in the gas diffusion layer. Alternatively, a catalyst having water electrolysis activity prepared in the same manner as described above is supported on electron conductive particles; iridium chloride (IrCl ₄ · H ₂ O), iridium chloride (H ₂ IrCl ₆ · 6H _2). O) and iridium resin acid are dissolved in a solvent such as water, ethanol, or butanol to prepare an iridium precursor solution. The iridium precursor solution is applied to electron conductive particles, and this is applied to an oxygen atmosphere ( For example, heat treatment under conditions of oxygen partial pressure of 0.1 to 0.5 atm and temperatures of 200 to 800 ° C. for 5 to 120 minutes; iridium complexes (for example, Na ₂ IrO _In the method of applying the slurry, an electrode obtained by immersing electron conductive particles in the aqueous solution ₄ and electrodepositing iridium oxide (IrO ₂ ) is used as a catalyst having water electrolysis activity. May be used.

  As a base material used for the gas diffusion layer used in the form (a) above, any conventionally known base material can be used without particular limitation. Specifically, a sheet-like material having conductivity and porosity such as a carbon woven fabric, a paper-like paper body, a felt, and a non-woven fabric; a metal mesh, and the like can be given. More specifically, carbon cloth, carbon paper (carbon paper), carbon cloth, carbon non-woven fabric, and metal mesh can be preferably used, and carbon cloth, carbon paper (carbon paper), carbon non-woven fabric, and metal mesh are more preferable. These materials have high electronic conductivity, and can significantly suppress / prevent a decrease in cell performance accompanying an increase in insulation resistance (IR). Moreover, the base material used for a gas diffusion layer can also use a commercial item, for example, carbon paper TGP series by Toray Industries, Inc., carbon cloth by E-TEK, etc. are mentioned. The thickness of the substrate is not particularly limited as long as it can sufficiently suppress and prevent the flooding phenomenon. Specifically, the thickness of the substrate used for the gas diffusion layer is preferably 100 to 500 μm, more preferably 150 to 400 μm, and most preferably 200 to 350 μm. With such a thickness, both the mechanical strength and drainage of the gas diffusion layer can be sufficiently secured.

  The gas diffusion layer preferably contains a water repellent in the base material for the purpose of further improving water repellency and preventing a flooding phenomenon. Although it does not specifically limit as said water repellent, It is fluorine-type, such as a polytetrafluoroethylene (PTFE), a polyvinylidene fluoride (PVDF), a polyhexafluoropropylene, a tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Examples thereof include polymer materials, polypropylene, and polyethylene. When a water repellent is contained in the gas diffusion layer, a general water repellent treatment method may be used. For example, after immersing the base material used for a gas diffusion layer in the dispersion | distribution aqueous solution or alcohol dispersion solution of a water repellent, the method of heat-drying in oven etc. is mentioned. In view of ease of exhaust gas treatment during drying, it is preferable to use a dispersed aqueous solution of a water repellent.

  The present invention is characterized in that a catalyst having water electrolysis activity is disposed at the interface between the gas diffusion layer and the catalyst layer. In this case, the catalyst having water electrolysis activity is not particularly limited as long as it can induce a water electrolysis reaction. For example, a simple metal selected from iridium, rhodium, ruthenium, and titanium; iridium oxide, rhodium oxide, ruthenium oxide, Examples thereof include oxides of the metal such as titanium oxide; and alloys containing the metal such as an alloy of iridium and ruthenium. Among these, a metal selected from iridium, rhodium, ruthenium and titanium, an oxide of the metal, and an alloy containing the metal are preferable. This is because iridium, rhodium, ruthenium, and titanium have a higher water electrolysis activity than other metals such as platinum, and therefore can provide a gas diffusion layer that can effectively suppress the flooding phenomenon. In addition, among the compounds having various metal forms, the simple metal, alloy, and oxide forms have higher water electrolysis activity than other forms, and thus the metal in such form has water electrolysis activity. By using it as a catalyst, a gas diffusion layer capable of suppressing the flooding phenomenon can be provided. More specifically, iridium, ruthenium, iridium oxide, ruthenium oxide, an alloy of iridium and ruthenium is more preferable, and iridium oxide, iridium, ruthenium, and ruthenium oxide are particularly preferable.

  The shape and size of the catalyst having water electrolysis activity are not particularly limited, and the same shape and size as known catalysts can be used. For example, the catalyst having water electrolysis activity includes substantially granular and elliptical shapes. In this case, the average particle diameter of the catalyst having water electrolysis activity in the case of granular is not particularly limited, but the average particle diameter is preferably 1 to 10 nm, more preferably 3 to 5 nm. If it is such a range, the catalyst which has water electrolysis activity can exhibit sufficient water electrolysis activity, and can electrolyze the water produced | generated in the catalyst layer efficiently. The “average particle size of the catalyst having water electrolysis activity” in the present invention is the particle size of the catalyst component determined from the crystallite size or transmission electron microscope image obtained from the half-value width of the diffraction peak of the catalyst component in X-ray diffraction It can be measured by the average value of the diameters.

  As described above, the present invention is characterized in that a catalyst having water electrolysis activity is disposed at the interface between the gas diffusion layer and the catalyst layer. Used. Hereinafter, although the preferable formation method of the gas diffusion electrode of this invention is described, this invention is not limited to the following method.

  In the present invention, the catalyst component used in the cathode catalyst layer is not particularly limited as long as it has a catalytic action for the oxygen reduction reaction, and known catalysts can be used in the same manner. Further, the catalyst component used in the anode catalyst layer is not particularly limited as long as it has a catalytic action for the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. Specifically, it is selected from platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum and the like, and alloys thereof. Is done. Among these, those containing at least platinum are preferably used in order to improve catalyst activity, poisoning resistance to carbon monoxide and the like, heat resistance, and the like. The composition of the alloy is preferably 30 to 90 atomic% for platinum and 10 to 70 atomic% for the metal to be alloyed, depending on the type of metal to be alloyed. The composition of the alloy when the alloy is used as a cathode catalyst varies depending on the type of metal to be alloyed and can be appropriately selected by those skilled in the art, but platinum is 30 to 90 atomic%, and other metals to be alloyed are 10 It is preferable to set it to -70 atomic%. In general, an alloy is a generic term for a metal element having one or more metal elements or non-metal elements added and having metallic properties. The alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any may be used in the present application. At this time, the catalyst component used for the cathode catalyst layer and the catalyst component used for the anode catalyst layer can be appropriately selected from the above. In the following description, unless otherwise specified, the description of the catalyst component for the cathode catalyst layer and the anode catalyst layer has the same definition for both, and is collectively referred to as “catalyst component”. However, the catalyst components for the cathode catalyst layer and the anode catalyst layer do not need to be the same, and are appropriately selected so as to exhibit the desired action as described above.

  The shape and size of the catalyst component are not particularly limited, and the same shape and size as known catalyst components can be used, but the catalyst component is preferably granular. At this time, the smaller the average particle diameter of the catalyst particles used in the catalyst ink, the higher the effective electrode area where the electrochemical reaction proceeds, which is preferable because the oxygen reduction activity is also high, but in practice the average particle diameter is too small. On the other hand, a phenomenon in which the oxygen reduction activity decreases is observed. Therefore, the average particle diameter of the catalyst particles contained in the catalyst ink is preferably 1 to 30 nm, more preferably 1.5 to 20 nm, still more preferably 2 to 10 nm, and particularly preferably 2 to 5 nm. It is preferably 1 nm or more from the viewpoint of easy loading, and preferably 30 nm or less from the viewpoint of catalyst utilization. The “average particle diameter of the catalyst particles” in the present invention is the average value of the particle diameter of the catalyst component determined from the crystallite diameter or transmission electron microscopic image obtained from the half width of the diffraction peak of the catalyst component in X-ray diffraction. Can be measured.

  In the present invention, the catalyst particles described above are included in the catalyst ink as an electrode catalyst supported on a conductive carrier.

  The conductive carrier may have any specific surface area for supporting the catalyst particles in a desired dispersed state and has sufficient electronic conductivity as a current collector. The main component is carbon. Preferably there is. Specific examples include carbon particles made of carbon black, activated carbon, coke, natural graphite, artificial graphite and the like. In the present invention, “the main component is carbon” refers to containing a carbon atom as a main component, and is a concept including both a carbon atom only and a substantially carbon atom. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, being substantially composed of carbon atoms means that mixing of impurities of about 2 to 3% by mass or less is allowed.

The BET specific surface area of the conductive carrier may be a specific surface area sufficient to carry the catalyst component in a highly dispersed state, but is preferably 20 to 1600 m ² / g, more preferably 80 to 1200 m ² / g. Is good. When the specific surface area is in the above range, the dispersibility of the catalyst component and the polymer electrolyte in the conductive support is good, sufficient power generation performance is obtained, and sufficient catalyst component and polymer electrolyte are effective. Utilization rate can be achieved.

  Further, the size of the conductive carrier is not particularly limited, but from the viewpoint of controlling the ease of loading, the catalyst utilization, and the thickness of the electrode catalyst layer within an appropriate range, the average particle size is 5 to 200 nm. The thickness is preferably about 10 to 100 nm.

  In the electrode catalyst in which the catalyst component is supported on the conductive support, the supported amount of the catalyst component is preferably 10 to 80% by mass, more preferably 30 to 70% by mass with respect to the total amount of the electrode catalyst. Good. When the supported amount is in the above range, high dispersibility of the catalyst component on the conductive support, improvement in excellent power generation performance, and satisfactory catalytic activity per unit mass can be obtained. The amount of the catalyst component supported can be examined by inductively coupled plasma emission spectroscopy (ICP).

  The cathode catalyst layer / anode catalyst layer (hereinafter also simply referred to as “catalyst layer”) of the present invention contains a polymer electrolyte in addition to the electrode catalyst. The polymer electrolyte is not particularly limited, and a known one can be used, but any member having at least high proton conductivity may be used. The polymer electrolyte that can be used in this case is roughly classified into a fluorine-based electrolyte that contains fluorine atoms in the whole or a part of the polymer skeleton and a hydrocarbon-based electrolyte that does not contain fluorine atoms in the polymer skeleton.

  Specific examples of the fluorine electrolyte include perfluorocarbon sulfonic acids such as Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.). Polymer, polytrifluorostyrene sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene A preferred example is a fluoride-perfluorocarbon sulfonic acid-based polymer.

  Specific examples of the hydrocarbon electrolyte include polysulfone sulfonic acid, polyaryl ether ketone sulfonic acid, polybenzimidazole alkyl sulfonic acid, polybenzimidazole alkyl phosphonic acid, polystyrene sulfonic acid, polyether ether ketone sulfonic acid, polyphenyl. A suitable example is sulfonic acid.

  The polymer electrolyte preferably contains a fluorine atom because of its excellent heat resistance and chemical stability. Among them, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.) Fluorine electrolytes such as Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) are preferred.

  The catalyst component can be supported on the conductive carrier by a known method. For example, known methods such as impregnation method, liquid phase reduction support method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle (microemulsion method) can be used. Alternatively, a commercially available electrode catalyst may be used.

  In the method of the present invention, the catalyst ink comprising the electrode catalyst, the polymer electrolyte and the solvent as described above is applied to the surface of the layer having a catalyst having water electrolysis activity formed on the gas diffusion layer, or the catalyst having water electrolysis activity. Is applied to the surface of the gas diffusion layer previously disposed at a predetermined position (in this case, the catalyst layer is formed on the side where the catalyst having water electrolysis activity is disposed), whereby the catalyst layer is formed. In this case, the solvent is not particularly limited, and usual solvents used for forming the catalyst layer can be used in the same manner. Specifically, water, lower alcohols such as cyclohexanol, ethanol and 2-propanol can be used. Also, the amount of solvent used is not particularly limited, and the same amount as known can be used. In the catalyst ink, the electrode catalyst has a desired action, that is, hydrogen oxidation reaction (anode side) and oxygen reduction reaction. Any amount may be used as long as it can sufficiently exert the action of catalyzing (cathode side). It is preferable that the electrode catalyst is present in the catalyst ink in an amount of 5 to 30% by mass, more preferably 9 to 20% by mass.

  The catalyst ink of the present invention may contain a thickener. The use of a thickener is effective when the catalyst ink cannot be successfully applied onto a transfer mount. The thickener that can be used in this case is not particularly limited, and a known thickener can be used. Examples thereof include glycerin, ethylene glycol (EG), polyvinyl alcohol (PVA), and propylene glycol (PG). The amount of the thickener added when the thickener is used is not particularly limited as long as it does not interfere with the above effect of the present invention, but is preferably 5 to 20 with respect to the total mass of the catalyst ink. % By mass.

  The catalyst ink of the present invention is not particularly limited in its preparation method as long as an electrode catalyst, an electrolyte and a solvent, and if necessary, a water-repellent polymer and / or a thickener are appropriately mixed. For example, a catalyst ink can be prepared by adding an electrolyte to a polar solvent, heating and stirring the mixed solution to dissolve the electrolyte in the polar solvent, and then adding an electrode catalyst thereto. Alternatively, after the electrolyte is once dispersed / suspended in a solvent, the dispersion / suspension may be mixed with an electrode catalyst to prepare a catalyst ink. In addition, a commercially available electrolyte solution (for example, DuPont Nafion solution: Nafion dispersed / suspended at a concentration of 5 wt% in 1-propanol) in which the electrolyte has been prepared in the above-mentioned other solvent in advance is used as it is. May be used in the method.

  The catalyst ink composed of the polymer electrolyte and the solvent as described above is formed on the surface of the layer having a catalyst having water electrolysis activity formed on the gas diffusion layer, or the catalyst having water electrolysis activity is previously disposed at a predetermined position. Each catalyst layer is formed by coating on the surface of the gas diffusion layer (in this case, the catalyst layer is formed on the side where the catalyst having water electrolysis activity is disposed). At this time, the conditions for forming the cathode / anode catalyst layer on the polymer electrolyte membrane are not particularly limited, and can be used in the same manner as known methods or appropriately modified. For example, the catalyst ink is applied onto the polymer electrolyte membrane so that the thickness after drying is 5 to 20 μm, and is 25 to 150 ° C., more preferably 60 to 120 ° C. in a vacuum dryer or under reduced pressure. And drying for 5 to 30 minutes, more preferably for 10 to 20 minutes. In addition, in the said process, when the thickness of a catalyst layer is not enough, the said application | coating and drying process is repeated until it becomes desired thickness.

  The gas diffusion electrode of the present invention thus obtained has a structure in which a catalyst having water electrolysis activity is disposed at the interface between the catalyst layer and the gas diffusion layer. For this reason, since the catalyst having water electrolysis activity catalyzes the water electrolysis reaction in the vicinity of the interface, it is easy to attract water from the catalyst layer, thereby forming a water vapor concentration gradient from the catalyst layer to the gas diffusion layer. Due to such a gradient, the moisture moves from the catalyst layer having a large amount of moisture to the gas diffusion layer having a small amount of moisture, and the movement of such moisture causes the catalyst layer, particularly the cathode-side electrode catalyst layer which has been a problem in the past. Water retention does not occur or is difficult to occur. Therefore, the gas diffusion electrode of the present invention has a flooding phenomenon that clogs pores that have been a reaction gas supply path in the catalyst layer, particularly the cathode side electrode catalyst layer, particularly a flooding phenomenon at a high current density; Particularly, corrosion of carbon in the electrode catalyst layer on the cathode side can be effectively suppressed / prevented. Therefore, the gas diffusion electrode of the present invention can be suitably used for an electrolyte membrane-electrode assembly, particularly an electrolyte membrane-electrode assembly for a fuel cell.

  Accordingly, the second aspect of the present invention includes an electrolyte membrane, a cathode side gas diffusion electrode disposed on one side of the electrolyte membrane, and an anode side gas diffusion electrode disposed on the other side of the electrolyte membrane. The present invention relates to an electrolyte membrane-electrode assembly, wherein at least one of a cathode side gas diffusion electrode and an anode side gas diffusion electrode is the gas diffusion electrode of the present invention. As described above, the present invention intends to solve the problem of flooding phenomenon and carbon corrosion particularly occurring on the cathode side. For this reason, it is preferable to use the gas diffusion electrode of the present invention at least for the cathode side gas diffusion electrode, and more preferably, the gas diffusion electrode of the present invention is used for both the cathode and anode side gas diffusion electrodes.

  The electrolyte membrane-electrode assembly of the present invention uses the first gas diffusion electrode of the present invention as at least one of the cathode side and anode side gas diffusion electrodes, and the other members are the same as in the conventional case. A manufacturing method can be applied. Hereinafter, preferred embodiments of the electrolyte membrane-electrode assembly (MEA) of the present invention will be described. However, the present invention is not limited to the following embodiment. In the following embodiment, the gas diffusion electrodes of both the anode and the cathode are the gas diffusion electrodes of the present invention, but a general gas diffusion layer may be used for any one of the gas diffusion electrodes, In this case, a known gas diffusion layer and its formation method are applied in the same manner.

  The MEA of the present invention can be obtained by forming a laminate by sandwiching the electrolyte membrane with the gas diffusion electrode of the present invention and performing hot pressing on the laminate. At this time, the hot press conditions are not particularly limited as long as the electrode catalyst layer and the electrolyte membrane can be sufficiently closely joined, but are 100 to 200 ° C., more preferably 110 to 170 ° C. It is preferable to carry out at a press pressure of 5 MPa. Thereby, the bondability between the electrolyte membrane and the electrode catalyst layer can be enhanced.

  The electrolyte membrane used for the MEA of the present invention is not particularly limited, and examples thereof include a membrane made of the same polymer electrolyte as that used for the catalyst layer. In addition, various Nafion (registered trademark of DuPont) manufactured by DuPont and perfluorosulfonic acid membranes represented by Flemion, ion exchange resins manufactured by Dow Chemical, ethylene-tetrafluoroethylene copolymer resin membrane, trifluoro Fluoropolymer electrolytes such as resin membranes based on styrene, hydrocarbon resin membranes with sulfonic acid groups, and other commonly available solid polymer electrolyte membranes and polymer microporous membranes A membrane impregnated with a liquid electrolyte, a membrane in which a porous body is filled with a polymer electrolyte, or the like may be used. The polymer electrolyte used for the polymer electrolyte membrane and the polymer electrolyte used for each electrode catalyst layer may be the same or different, but the adhesion between each electrode catalyst layer and the polymer electrolyte membrane From the viewpoint of improving the properties, it is preferable to use the same one.

  The thickness of the electrolyte membrane used in the MEA of the present invention may be appropriately determined in consideration of the properties of the obtained MEA, but is preferably 5 to 300 μm, more preferably 10 to 200 μm, and particularly preferably 15 to 100 μm. is there. From the viewpoint of strength during film formation and durability during MEA operation, it is preferably 5 μm or more, and from the viewpoint of output characteristics during MEA operation, it is preferably 300 μm or less.

  Further, as the electrolyte membrane, in addition to the above-described fluorine-based polymer electrolyte and a membrane made of a hydrocarbon resin having a sulfonic acid group, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc. You may use what formed the porous thin film impregnated with electrolyte components, such as phosphoric acid and an ionic liquid.

  In the above, the method for manufacturing the MEA of the present invention by the transfer method has been described. First, after forming a catalyst layer on the electrolyte membrane, this is formed on the gas diffusion layer formed as described above. Forming a layer having a catalyst having a water electrolysis activity and further forming a gas diffusion layer on the layer having a catalyst having the catalyst having the water electrolysis activity; or after forming the catalyst layer on the electrolyte membrane, A gas diffusion layer in which a catalyst having water electrolysis activity is previously placed in a predetermined position is laminated so that the catalyst layer and the side on which the catalyst having water electrolysis activity is placed are combined, and this is heated. The MEA of the present invention may be manufactured by bonding with a press or the like. At this time, the method for forming the catalyst layer on the electrolyte membrane is not particularly limited, and a known method can be applied. Specifically, (A) a method of applying the catalyst ink as described above on the electrolyte membrane to form a cathode and an anode catalyst layer, respectively; (B) a transfer mount of the catalyst ink as prepared above. It is preferable to use a method in which a cathode and an anode catalyst layer are respectively formed by coating and drying, and an electrolyte membrane is sandwiched between these catalyst layers, followed by hot pressing of this laminate. In the above method (A), the conditions for forming the cathode / anode catalyst layer on the electrolyte membrane are not particularly limited, and known methods can be used in the same manner or with appropriate modifications. For example, the catalyst ink is applied onto the polymer electrolyte membrane so that the thickness after drying is 5 to 20 μm, and is 25 to 150 ° C., more preferably 60 to 120 ° C. in a vacuum dryer or under reduced pressure. And drying for 5 to 30 minutes, more preferably for 10 to 20 minutes. In addition, in the said process, when the thickness of a catalyst layer is not enough, the said application | coating and drying process is repeated until it becomes desired thickness. In the method (B), a known sheet such as a polyester sheet such as a PTFE (polytetrafluoroethylene) sheet or a PET (polyethylene terephthalate) sheet can be used as the transfer mount. The transfer mount is appropriately selected according to the type of catalyst ink to be used (particularly, a conductive carrier such as carbon in the ink). In the above process, the thickness of the electrode catalyst layer is not particularly limited as long as it can sufficiently exhibit the catalytic action of the hydrogen oxidation reaction (anode side) and the oxygen reduction reaction (cathode side). Thickness can be used. Specifically, the thickness of the electrode catalyst layer is 1 to 30 μm, more preferably 1 to 20 μm. The method for applying the catalyst ink onto the transfer mount is not particularly limited, and a known method such as a screen printing method, a deposition method, or a spray method can be similarly applied. Also, the drying conditions of the applied electrode catalyst layer are not particularly limited as long as the polar solvent can be completely removed from the electrode catalyst layer. Specifically, the catalyst ink coating layer (electrode catalyst layer) is dried in a vacuum dryer at room temperature to 100 ° C., more preferably 50 to 80 ° C., for 30 to 60 minutes. At this time, if the thickness of the catalyst layer is not sufficient, the coating and drying process is repeated until a desired thickness is obtained. Next, after sandwiching the electrolyte membrane between the catalyst layers, the conditions for hot pressing the laminate are not particularly limited as long as the catalyst layer and the electrolyte membrane can be joined sufficiently closely, but the temperature is 100 to 200 ° C. It is preferably performed at 110 to 170 ° C. and a pressing pressure of 1 to 5 MPa with respect to the electrode surface. Thereby, the bondability between the polymer electrolyte membrane and the electrode catalyst layer can be enhanced. After performing the hot press, the MEA composed of the electrode catalyst layer and the polymer electrolyte membrane can be obtained by removing the transfer mount.

  As described above, the electrolyte membrane-electrode assembly of the present invention has a flooding phenomenon that clogs pores that have become reaction gas supply paths in the catalyst layer, particularly the cathode-side electrode catalyst layer, particularly a flooding phenomenon at a high current density; Furthermore, carbon corrosion, particularly corrosion of carbon in the electrode catalyst layer on the cathode side, can be effectively suppressed / prevented. By using such an electrolyte membrane-electrode assembly, a highly reliable fuel cell having excellent durability can be provided. Accordingly, a third aspect of the present invention relates to a fuel cell using the electrolyte membrane-electrode assembly of the present invention. The fuel cell of the present invention has high drainage performance during normal operation while suppressing carbon corrosion, and the catalyst layer does not cause flooding.

  In the fuel cell of the present invention, oxygen, ozone and hydrogen peroxide are produced by the water electrolysis reaction in the gas diffusion electrode of the present invention. These oxygen, ozone and hydrogen peroxide are gas diffusion layer and catalyst layer. There is a possibility of deteriorating the polymer electrolyte inside. For this reason, in the fuel cell of the present invention, it is preferable to instantaneously excessively supply the supply gas during startup, particularly immediately after startup, and purge and remove oxygen, ozone and hydrogen peroxide. Thereby, it is possible to effectively suppress and prevent the catalyst layer and the gas diffusion layer from being adversely affected by the above-mentioned undesirable by-product gases (oxygen, ozone and hydrogen peroxide).

  The type of the fuel cell is not particularly limited. In the above description, the polymer electrolyte fuel cell has been described as an example, but in addition to this, a representative example is an alkaline fuel cell and a phosphoric acid fuel cell. Examples thereof include an acid electrolyte fuel cell, a direct methanol fuel cell, and a micro fuel cell. Among them, a polymer electrolyte fuel cell is preferable because it is small in size, and can achieve high density and high output. The fuel cell is useful as a stationary power source in addition to a power source for a moving body such as a vehicle in which a mounting space is limited. However, the fuel cell is particularly useful for an automobile application in which system start / stop and output fluctuation frequently occur. It can be particularly preferably used.

  The polymer electrolyte fuel cell is useful not only as a stationary power source but also as a power source for a moving body such as an automobile having a limited mounting space. In particular, moving bodies such as automobiles that are susceptible to corrosion of the carbon support due to the high output voltage required after a relatively long shutdown, and deterioration of the polymer electrolyte due to the high output voltage being taken out during operation. It is particularly preferred to be used as a power source.

  The configuration of the fuel cell is not particularly limited, and a conventionally known technique may be used as appropriate. Generally, the fuel cell has a structure in which an MEA is sandwiched between separators.

  The separator can be used without limitation as long as it is conventionally known, such as those made of carbon such as dense carbon graphite and a carbon plate, and those made of metal such as stainless steel. The separator has a function of separating air and fuel gas, and a channel groove for securing the channel may be formed. The thickness and size of the separator, the shape of the flow channel, and the like are not particularly limited, and may be appropriately determined in consideration of the output characteristics of the obtained fuel cell.

  Further, in order to prevent the gas supplied to each catalyst layer from leaking to the outside, a gas seal portion may be further provided at a portion where the catalyst layer is not formed on the gasket layer. Examples of the material constituting the gas seal portion include rubber materials such as fluoro rubber, silicon rubber, ethylene propylene rubber (EPDM), polyisobutylene rubber, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoro. Fluorine polymer materials such as propylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and thermoplastic resins such as polyolefin and polyester. In addition, the thickness of the gas seal portion may be about 50 μm to 2 mm, preferably about 100 μm to 1 mm.

  Furthermore, a stack in which a plurality of MEAs are stacked via a separator and connected in series may be formed so that the fuel cell can obtain a desired voltage or the like. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

Example 1
A carbon paper having a thickness of 270 μm (TGP-H-090 manufactured by Toray Industries, Inc.) was immersed in a polytetrafluoroethylene (PTFE) dispersion (polyflon D-1E manufactured by Daikin Industries, 60% by weight) for 30 minutes, and then in an oven. By drying at 80 ° C. for 1 hour, PTFE was dispersed in the carbon paper to prepare a water-repellent gas diffusion layer. At this time, the PTFE content in the gas diffusion layer was 25 wt%.

Next, 5.4 g of Vulcan XC72R (manufactured by CABOT) as the electron conductive particles, 1.0 g of PTFE dispersion (polyflon D-1E, 60% by weight, manufactured by Daikin Industries, Ltd.), 0.5 g of iridium chloride (IV) acid solution Then, 29.6 g of water was mixed and dispersed using a homogenizer for 3 hours to form a slurry. This slurry was applied to one side of the carbon paper treated with water repellency using a bar coater so that the thickness after drying was 50 μm, and then dried in an oven at 80 ° C. for 1 hour, and further muffled. Heat treatment was performed at 350 ° C. for 1 hour in a furnace. As a result, the mass of the formed layer per 1 cm ^{2 of} carbon paper was 3.0 mg. Thereafter, a gas diffusion layer in which a layer having a catalyst having water electrolysis activity was formed by cutting into a square having a side of 6 cm was obtained.

  53.9 g of platinum-supported carbon microparticles (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) (platinum content: 49% by weight) 43.9 g of a commercially available Nafion solution (dispersed / suspended Nafion at a concentration of 5 wt%, manufactured by Aldrich) The mass of the solid polymer electrolyte is 0.86) with respect to the mass 1 of the total conductive carbon in the catalyst layer, 12.5 g of pure water, and 5 g of 2-propanol. A cathode and anode catalyst layer ink was obtained by mixing and dispersing in a glass container for 3 hours using a homogenizer.

  The catalyst ink prepared above was applied onto a Teflon sheet (size: 5 cm × 5 cm) with a screen printer and dried with a vacuum dryer for 1 hour to prepare a transfer sheet. At this time, the above process was repeated until the amount of platinum in the catalyst layer reached 10 mg, and overcoating was performed. The electrolyte membrane (NR-211, manufactured by DuPont, thickness 25 μm) was sandwiched between the two transfer sheets prepared above so that the catalyst layer was in contact with the electrolyte membrane, and hot at 130 ° C. and 2 MPa for 10 minutes. A press was performed. After hot pressing, the Teflon sheet was peeled off to obtain a laminate in which the membrane, the anode catalyst layer, and the cathode catalyst layer were laminated.

The two layers of the gas diffusion layer formed as described above, each having a layer having a catalyst having water electrolysis activity, were formed into a catalyst layer and a layer having a catalyst having water electrolysis activity. As shown in FIG. 1, sandwiching was performed and hot pressing was performed at 130 ° C. and 2 MPa for 10 minutes to produce a small subscale MEA (5 cm × 5 cm: electrode area 25 cm ² ) as shown in FIG.

Comparative Example 1
In Example 1, except for not adding an iridium chloride (IV) acid solution, a comparative sub-scale MEA (5 cm × 5 cm: electrode area 25 cm ² ) was prepared according to the method described in Example 1.

Evaluation Test: Performance Evaluation The current-voltage characteristics of the MEA produced in Example 1 and the comparative MEA produced in Comparative Example 1 were evaluated under the conditions shown in Table 1 under normal pressure. The current-voltage characteristic is a test for observing a change in output voltage at that time by forcibly promoting a reaction by applying a load current from the outside to a cell in a generated state. The output voltage changes because the fuel cell reaction causes an overvoltage to be generated at the cathode and the anode, and a resistance is generated in the battery by causing a current to flow.

  The results are shown in FIG. FIG. 2 shows that when the MEA of Example 1 having the gas diffusion electrode according to the present invention is used, a decrease in output voltage can be significantly suppressed even at a high current density as compared with the comparative MEA of Comparative Example 1. . This is because, in the MEA of Example 1, the catalyst having water electrolysis activity arranged at the interface between the gas diffusion layer and the catalyst layer forms a water concentration gradient, and the generated water in the catalyst layer is smoothly discharged. It is considered that this is because power is generated without causing the flooding phenomenon. On the other hand, in the comparative MEA of Comparative Example 1 in which no catalyst having water electrolysis activity is arranged, the electrode catalyst in the catalyst layer is exposed to a high potential at the cathode, so that the oxide state exists more stably. However, since metal oxides have polarity, they tend to attract moisture, that is, they are hydrophilic, so they tend to attract moisture around them, and the generated water in the catalyst layer is not drained well. It is considered that the output voltage decreases under high current density.

FIG. 3 is a schematic view of the cathode side of the small subscale MEA of Example 1. FIG. It is a graph which shows the current-voltage characteristic in an evaluation test.

Claims (12)

  A gas diffusion electrode comprising a gas diffusion layer and a catalyst layer, wherein a catalyst having water electrolysis activity is disposed at an interface between the gas diffusion layer and the catalyst layer, and the layer having a catalyst having water electrolysis activity comprises the gas diffusion layer and the catalyst A cathode-side gas diffusion electrode, wherein the total thickness of the gas diffusion layer and the layer having a catalyst having water electrolysis activity, which is inserted between the layers, is 100 to 500 μm.   The cathode-side gas diffusion electrode according to claim 1, wherein the layer having a catalyst having water electrolysis activity further includes electron conductive particles. The cathode-side gas diffusion electrode according to claim 2, wherein the electron conductive particles are at least one carbon particle selected from the group consisting of carbon black, acetylene black, and activated carbon . The cathode side gas diffusion electrode according to any one of claims 1 to 3, wherein the gas diffusion layer is a carbon cloth, carbon paper, a nonwoven fabric, or a metal mesh .   The cathode-side gas diffusion electrode according to any one of claims 1 to 4, wherein the catalyst having water electrolysis activity is disposed in a large amount on a side in contact with the catalyst layer in a layer having a catalyst having water electrolysis activity. .   The cathode-side gas diffusion electrode according to any one of claims 1 to 5, wherein the layer having a catalyst having water electrolysis activity does not contain crystalline carbon fibers and carbon whiskers.   A gas diffusion electrode comprising a gas diffusion layer and a catalyst layer, wherein a catalyst having water electrolysis activity is disposed at an interface between the gas diffusion layer and the catalyst layer, and the catalyst having water electrolysis activity is disposed in the gas diffusion layer. The cathode gas diffusion electrode, wherein the gas diffusion layer has a thickness of 100 to 500 μm.   The cathode-side gas diffusion electrode according to claim 7, wherein a large amount of the catalyst having water electrolysis activity is disposed on a side in contact with the catalyst layer in the gas diffusion layer.   The cathode-side gas diffusion electrode according to claim 7 or 8, wherein the gas diffusion layer does not contain crystalline carbon fibers and carbon whiskers.   The catalyst having water electrolysis activity is at least one selected from the group consisting of a metal selected from iridium, rhodium, ruthenium and titanium, an oxide of the metal, and an alloy containing the metal. The cathode-side gas diffusion electrode according to any one of the above. An electrolyte membrane-electrode assembly having an electrolyte membrane, a cathode side gas diffusion electrode disposed on one side of the electrolyte membrane, and an anode side gas diffusion electrode disposed on the other side of the electrolyte membrane, An electrolyte membrane-electrode assembly, wherein the cathode-side gas diffusion electrode is the gas diffusion electrode according to any one of claims 1 to 10.   A fuel cell comprising the electrolyte membrane-electrode assembly according to claim 11.

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