JP2004259463A - Manufacturing method of gas diffusion layer of solid polymer type fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a gas diffusion layer of a solid polymer type fuel cell capable of stably carrying out sufficient smoothing of a gas diffusion layer surface on the side adjacent to a catalyst layer, and thereby allowing a stable long-time continuous operation of the fuel cell. <P>SOLUTION: In this manufacturing method of the gas diffusion layer of the solid polymer type fuel cell provided with the catalyst layers disposed on both principal surfaces by interposing a solid polymer electrolyte film, and the porous gas diffusion layers disposed on both outer sides of the catalyst layer, each gas diffusion layer is formed of a conductive porous base material such as carbon paper or carbon cloth; the base material is formed into a predetermined size; thereafter the base material surface on the side adjacent to the catalyst layer is smoothed by arc heat of discharge. For instance, the base material 11 is used as a positive electrode; a graphite electrode 15 is used as a negative electrode; a pulse voltage is applied between both the electrodes in a working solution 16 from an arc generator 17; and thereby the arc heat of discharge is generated to smooth the base material surface by melting carbon fibers projecting rom the base material surface. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a gas diffusion layer in a polymer electrolyte fuel cell.
[0002]
[Prior art]
A fuel cell is a device that uses hydrogen and oxygen to generate power through an electrolyte. The polymer electrolyte fuel cell uses a resin membrane that exhibits ionic conductivity when the polymer membrane contains water as an electrolyte. FIG. 4 shows a perspective view of the configuration of the fuel cell, and FIG. FIG. 3 is an enlarged sectional view.
[0003]
3 and 4, a catalyst layer 2 and a porous gas diffusion layer 3 are provided on both sides of the solid polymer electrolyte membrane 1, and one of the gas diffusion layers contains a fuel containing hydrogen as a reaction gas. A separator 5 having a fuel gas flow path for supplying and discharging a gas and having an oxidizing gas flow path for supplying and discharging an oxidizing gas as a reaction gas to the other diffusion layer is provided. In FIG. 4, the separator has a reaction gas flow path on both sides of one separator. However, for manufacturing reasons, a separator having a flow path on one side is stacked back to back as shown in FIG. In some cases. A stack of many of the above cells is called a stack.
[0004]
As the solid polymer electrolyte membrane 1, for example, a perfluorosulfonic acid polymer membrane (Dupont, USA, trade name: Nafion membrane) is used. This membrane exhibits specific resistance of 20 Ω · cm or less at room temperature by being saturated with water, and functions as a proton conductive electrolyte. The saturated water content of the membrane changes reversibly with temperature.
[0005]
By supplying hydrogen from one side of the gas diffusion layer 3 bonded to both sides of the polymer electrolyte membrane 1 and oxygen or air from the other side, oxidation of hydrogen at the interface between the polymer electrolyte membrane 1 and the catalyst layer 2 is performed. Proton and electron transfer occur by the reaction and the reduction reaction of oxygen, and electricity can be obtained.
[0006]
The catalyst layer 2 is formed from particulate platinum black or platinum-carrying carbon and a water-repellent fluororesin. As the catalyst layer 2, a catalyst with an electrolyte resin having a configuration in which a solid polymer electrolyte resin is mixed in the catalyst layer is often used in order to increase the reaction area of the catalyst.
[0007]
As the gas diffusion layer 3, conductive carbon paper or carbon cloth is used. Usually, after forming a joined body of the solid polymer electrolyte membrane 1 and the catalyst layer 2, the gas diffusion layer 3 is joined by hot pressing. After the catalyst layer 2 is applied on the gas diffusion layer 3 and joined, In some cases, a joined body with the solid polymer electrolyte membrane 1 is formed.
[0008]
The gas diffusion layer 3 will be described in more detail. In order to obtain high power generation efficiency, when the reaction gas (H ₂ , O ₂ ) moves from the reaction gas flow path to the catalyst layer 2 by diffusion and reacts on the platinum surface in the catalyst layer, the reaction gas (H ₂ , O ₂ ) It is necessary to supply the reaction gas evenly to For this purpose, the gas diffusion layer 3 is provided between the reaction gas flow path and the catalyst layer 2 as described above. The gas diffusion layer 3 is made of a conductive porous material, and is generally formed of cloth or paper having a thickness of several hundred μm made of carbon fibers of several μm.
[0009]
FIG. 2 shows a schematic configuration diagram of the gas diffusion layer. The gas diffusion layer is formed by using only a conductive porous substrate such as carbon paper or carbon cloth (FIG. 2A), or when a carbon water repellent layer is formed on the substrate (FIG. 2A). 2 (b)).
[0010]
In the case of FIG. 2A, a large number of carbon fibers 13 are entangled to form a conductive porous base material 11, and this base material is formed into a predetermined size to form a gas diffusion layer. In order to reduce the contact resistance between the catalyst layer and the gas diffusion layer, the gas diffusion layer shown in FIG. 2B has a carbon water repellent layer 12 made of carbon particles and a water repellent, for example, having a thickness of several tens μm. , Formed on the surface of the base material 11 on the catalyst layer side.
[0011]
By the way, as described above, when a cloth or paper made of carbon fibers of several μm and having a thickness of several hundred μm is used for the gas diffusion layer, the carbon fibers may protrude from the surface of the base material. In a fuel cell stack, in order to prevent loss of output due to an increase in contact resistance between electrode members including a gas diffusion layer, each stacked member of the stack is pressurized and tightened in the stacking direction.
[0012]
When the battery stack is tightened, the carbon fiber 13 protruding from the surface of the base material 11 may damage the catalyst layer 2 and the solid polymer electrolyte membrane 1 and cause pinholes. In this case, a cross leak of the reaction gas between the fuel electrode and the air electrode may occur, and stable operation may not be performed. Even when the carbon water repellent layer 12 is formed on the catalyst layer side, the same problem occurs when the carbon fibers 13 protrude from the surface of the carbon water repellent layer 12.
[0013]
In order to solve the above problem, Patent Document 1 discloses the following manufacturing method. That is, the electrode is formed by forming a water-repellent carbon layer on the surface of the carbon cloth and then flattening the surface by hot pressing to form a gas diffusion layer, and then disposing a catalyst layer adjacent to the water-repellent carbon layer. (For details, see Patent Document 1).
[0014]
[Patent Document 1]
JP 2001-85019 A (pages 2-3)
[0015]
[Problems to be solved by the invention]
By the way, according to the method of manufacturing the electrode described in Patent Document 1 described above, mainly, the gas diffusion layer, although the surface of the base material can be flattened to some extent by hot pressing, it protrudes from the base material surface. Since the carbon fiber is warped, the desired flattening or smoothing is not performed, and there is a possibility that the catalyst layer and the solid polymer electrolyte membrane may be damaged.
[0016]
Further, when flattening is performed by hot pressing as in the method of Patent Document 1, at least a part of the gas diffusion layer is plastically deformed by hot pressing. Therefore, appropriate management is required to stably obtain dimensional accuracy. Required.
[0017]
The present invention has been made in view of the above points, and an object of the present invention is to make it possible to stably achieve a sufficient smoothing of the surface of a gas diffusion layer on the side adjacent to a catalyst layer, and to provide a fuel It is an object of the present invention to provide a method for producing a gas diffusion layer of a polymer electrolyte fuel cell which enables stable long-term continuous operation of a battery.
[0018]
[Means for Solving the Problems]
In order to solve the aforementioned problems, the present invention provides a catalyst layer disposed on both main surfaces with a solid polymer electrolyte membrane interposed therebetween, and a porous gas diffusion layer disposed on both outer sides of the catalyst layer. In the method for manufacturing a gas diffusion layer of a polymer electrolyte fuel cell provided, the gas diffusion layer is made of a conductive porous base material such as carbon paper or carbon cloth, and the conductive porous base material is After being formed to a predetermined size, the surface of the base material on the side adjacent to the catalyst layer is subjected to a smoothing treatment by arc heat of discharge (claim 1).
[0019]
According to the above, the carbon fibers protruding from the surface of the gas diffusion layer on the catalyst layer side can be burned off by electric discharge arc thermal processing, whereby the surface of the gas diffusion layer is smoothed. As a result, when the stack is tightened, the catalyst layer and solid polymer membrane are prevented from being damaged due to the gas diffusion layer, the reaction gas cross leak between the air electrode and the fuel electrode is less likely to occur, and the stack is stable for a long time. Continuous operation is possible.
[0020]
As an embodiment of the first aspect of the present invention, the following second to fifth aspects of the present invention are preferable. That is, in the manufacturing method according to claim 1, the smoothing treatment is performed by using the conductive porous base material as one electrode, and the graphite electrode as the other electrode, in an electrically insulating working fluid. Applying a pulse voltage between the two electrodes, thereby generating arc heat of discharge, and by this arc heat, melting and smoothing the carbon fibers protruding from the base material surface of the conductive porous base material; and (The invention of claim 2).
[0021]
As described above, when a metal electrode is used without using a graphite electrode, there is a problem that a melt of the electrode material adheres to the conductive porous substrate and adversely affects the performance of the gas diffusion layer. Although this may occur, the adverse effect is suppressed by using an electrode material of the same system as the conductive porous substrate. In addition, as the electric insulating working fluid, for example, kerosene used in general electric discharge machining can be used.
[0022]
Further, in the manufacturing method according to the second aspect, it is preferable that a gap between both electrode surfaces to which the pulse voltage is applied is 10 to 500 μm (the invention of the third aspect).
[0023]
Further, when a carbon water repellent layer is provided, the following claim 4 or 5 is provided. That is, in the manufacturing method according to any one of claims 1 to 3, after the smoothing treatment, a carbon water repellent layer is formed on the surface of the base material (the invention of claim 4). Alternatively, in the manufacturing method according to any one of claims 1 to 3, after the carbon water repellent layer is formed on the surface of the base material in advance, the smoothing treatment is performed (the invention of claim 5).
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0025]
FIG. 1 is a schematic explanatory view of a method for treating a surface of a gas diffusion layer according to an embodiment of the present invention, and shows an example in which the gas diffusion layer shown in FIG. 2A is applied. In FIG. 1, reference numeral 11 denotes a base material, 14 denotes an electric discharge machining reaction tank, 15 denotes a graphite electrode, 16 denotes a working liquid, and 17 denotes an arc generator.
[0026]
The electric discharge machining reaction tank 14 is filled with an electrically insulating machining fluid 6 (for example, kerosene), and the base material 11 and the graphite electrode 15 are arranged facing each other. Using the base material 11 as an anode and the graphite electrode 15 as a cathode, an arc is generated between the base material 11 and the graphite electrode 15 by electric discharge by an arc generator 17 provided with a pulse power supply. Due to the generated arc, the carbon fibers protruding from the surface of the base material 11 are burned out.
[0027]
The surface-to-surface distance between the substrate 11 and the graphite electrode 15 is adjusted according to the state of the carbon fibers protruding from the substrate surface. However, when the graphite electrode 5 comes into contact with the electrode surface, the surface of the substrate 11 may be burned out. If the distance is too long, there is a possibility that the effect of burning out the carbon fibers protruding from the substrate surface may not be obtained. From the above viewpoint, the preferable range of the gap between the two electrodes is 10 to 500 μm.
[0028]
In this embodiment, the surface treatment in the case where the gas diffusion layer is formed only with the base material 11 has been described, but the gas diffusion layer having the carbon water repellent layer shown in FIG. The surface treatment method is the same. Further, as described above, the carbon water repellent layer can be formed after the surface treatment shown in FIG.
[0029]
【The invention's effect】
As described above, according to the present invention, a solid comprising: a catalyst layer disposed on both main surfaces with a solid polymer electrolyte membrane interposed therebetween; and a porous gas diffusion layer disposed on both outer sides of the catalyst layer. In the method for producing a gas diffusion layer of a polymer fuel cell, when the gas diffusion layer is made of only a conductive porous substrate such as carbon paper or carbon cloth, the conductive porous substrate After forming the material to a predetermined size, the base material surface on the side adjacent to the catalyst layer is to be smoothed by arc heat of discharge,
When the gas diffusion layer is provided with a carbon water repellent layer, a carbon water repellent layer is formed after the smoothing treatment, or the smoothing treatment is performed after forming the carbon water repellent layer in advance. I decided to do it,
The surface of the gas diffusion layer adjacent to the catalyst layer can be sufficiently smoothed stably, and the fuel cell can be stably operated for a long time.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory view of a surface treatment method for a gas diffusion layer according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of a gas diffusion layer according to the present invention. FIG. 3 is a polymer electrolyte fuel cell. [FIG. 4] A perspective view of the configuration of a polymer electrolyte fuel cell [Description of symbols]
1: solid polymer electrolyte membrane, 2: catalyst layer, 3: gas diffusion layer, 5: separator, 11: base material, 12: carbon water repellent layer, 13: carbon fiber, 14: electric discharge machining reaction tank, 15: Graphite electrode, 16: working fluid, 17: arc generator.

Claims (5)

The gas diffusion layer of a polymer electrolyte fuel cell, comprising: a catalyst layer disposed on both main surfaces with a solid polymer electrolyte membrane interposed therebetween; and a porous gas diffusion layer disposed on both outer sides of the catalyst layer. In the manufacturing method of
The gas diffusion layer is formed of a conductive porous base material such as carbon paper or carbon cloth, and after forming the conductive porous base material to a predetermined size, the base material on the side adjacent to the catalyst layer is formed. A method for producing a gas diffusion layer of a polymer electrolyte fuel cell, wherein a surface is smoothed by arc heat of discharge. The manufacturing method according to claim 1, wherein the smoothing treatment is performed by using the conductive porous base material as one electrode and a graphite electrode as the other electrode in an electrically insulating working fluid between the two electrodes. A pulse voltage is applied to the conductive porous substrate, thereby generating arc heat of discharge, and the arc heat is used to melt and smooth carbon fibers protruding from the surface of the conductive porous substrate. A method for producing a gas diffusion layer of a polymer electrolyte fuel cell. 3. The method according to claim 2, wherein a gap between both electrode surfaces to which the pulse voltage is applied is set to 10 to 500 μm. 4. 4. The gas diffusion method for a polymer electrolyte fuel cell according to claim 1, wherein a carbon water repellent layer is formed on the surface of the base material after the smoothing treatment. 5. The method of manufacturing the layer. 4. The polymer electrolyte fuel cell according to claim 1, wherein the smoothing treatment is performed after forming a carbon water repellent layer on the surface of the base material in advance. 5. A method for producing a gas diffusion layer.

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