JP4052932B2 - Fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell, and more particularly to a fuel cell having a gas diffusion layer.
[0002]
[Prior art]
In recent years, fuel cells that have high energy conversion efficiency and do not generate harmful substances due to power generation reactions have attracted attention. As one of such fuel cells, a polymer electrolyte fuel cell that operates at a low temperature of 100 ° C. or lower is known.
[0003]
The polymer electrolyte fuel cell has a basic structure in which a polymer electrolyte membrane, which is an electrolyte membrane, is arranged between a fuel electrode and an air electrode. By supplying hydrogen to the fuel electrode and oxygen to the air electrode, Power is generated by the electrochemical reaction.
Fuel ^{_{electrode: H 2 → 2H + + 2e}} - (1)
Air electrode: 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
The fuel electrode and the air electrode have a structure in which a catalyst layer and a gas diffusion layer are laminated. The catalyst layers of the electrodes are arranged opposite to each other with the solid polymer film interposed therebetween, thereby constituting a fuel cell. The catalyst layer is a layer formed by binding carbon particles carrying a catalyst with an ion exchange resin. The gas diffusion layer becomes a passage for oxygen and hydrogen. The power generation reaction proceeds at a so-called three-phase interface of the catalyst, ion exchange resin and hydrogen in the catalyst layer.
[0004]
In the fuel electrode, hydrogen contained in the supplied fuel gas is decomposed into hydrogen ions and electrons as shown in the above formula (1). Among these, hydrogen ions move inside the solid polymer electrolyte membrane toward the air electrode, and electrons move to the air electrode through an external circuit. On the other hand, in the air electrode, oxygen contained in the supplied air reacts with hydrogen ions and electrons that have moved from the fuel electrode, and water is generated as shown in the above equation (2). Thus, electric power can be taken out by moving electrons from the fuel electrode toward the air electrode in the external circuit.
[0005]
In such a polymer electrolyte fuel cell, the gas diffusion layer supplies hydrogen gas or air supplied to the catalyst layer and plays a role of conducting electrons between the electrode and the external circuit. Therefore, the gas diffusion layer is preferably composed of a porous substrate having electrical conductivity, and is generally composed of a woven fabric, a nonwoven fabric, or paper made of conductive fibers such as carbon and metal. Although these are structurally different, they are basically a product in which a large number of fibers are stacked in the thickness direction, and electrical conduction in the thickness direction is performed through contact between the fibers. However, it has been pointed out that such a gas diffusion layer has a fiber that is not fixed to each other, so that electrical contact is unstable and stable electrical conductivity may not be obtained.
[0006]
Further, in order to improve the gas diffusibility of the gas diffusion layer, it is preferable to increase the space between the fibers and make them bulky, but this naturally reduces the contact points between the fibers. The gas diffusion layer is compressed by the compression process at the time of manufacturing the cell unit composed of the gas diffusion layer, the catalyst layer, and the electrolyte membrane, and tightening by the fuel cell stack, and the contact point between the fibers increases. In order to maintain gas diffusibility in the presence of water such as condensed water and product water, the carbon fiber surface is generally treated with water repellent treatment with fluororesin, and the carbon fiber surface is an insulator. Since it is partially covered, the effect of improving electrical conductivity due to compression decreases as the amount of water repellent treatment increases, which may lead to a decrease in electrical conductivity.
[0007]
In order to solve such problems, Japanese Patent Application Laid-Open No. 7-105957 discloses carbon fibers oriented in the thickness direction by mixing carbon fibers shorter than the electrode thickness into carbon fibers constituting the gas diffusion layer. A technique is described that improves the electrical conductivity.
[0008]
[Patent Document 1]
JP-A-7-105957
[Problems to be solved by the invention]
However, in the method described in Japanese Patent Laid-Open No. 7-105957, the carbon fibers oriented in the thickness direction are caused to assemble with the catalyst layer and the electrolyte membrane, tighten with the flow path substrate, operate, reduce the electrode thickness due to creep, etc. There is a risk of breaking through the catalyst layer and piercing the electrolyte membrane, generating pinholes in the electrolyte membrane. When pinholes are generated in the electrolyte membrane, the supplied oxygen gas and hydrogen gas react directly, and the power generation characteristics as a fuel cell are degraded.
[0010]
The present invention has been made in view of such circumstances, and an object thereof is to provide a gas diffusion layer excellent in electrical conductivity and a fuel cell including the gas diffusion layer.
[0011]
[Means for Solving the Problems]
One embodiment of the present invention relates to a fuel cell. This fuel cell is a fuel cell comprising an electrolyte membrane and a first electrode and a second electrode provided on the electrolyte membrane, wherein at least one of the first electrode or the second electrode is a single carbon. A gas diffusion layer including helical carbon fibers is provided, which is wound around the fibers with carbon fibers.
[0012]
Another aspect of the present invention also relates to a fuel cell. This fuel cell is a fuel cell comprising an electrolyte membrane and a first electrode and a second electrode provided on the electrolyte membrane, wherein at least one of the first electrode or the second electrode is a plurality of carbons. A gas diffusion layer including helical carbon fibers is provided, which is wound around the fibers with carbon fibers.
[0013]
The gas diffusion layer may be formed by forming the spiral carbon fiber into a woven fabric shape. The outer diameter of the helical carbon fiber may be 50% or more of the thickness of the gas diffusion layer. In that case, the gas diffusion layer may be formed by forming the helical carbon fibers into a nonwoven fabric or paper. In that case, the outer diameter of the helical carbon fiber may be 30% or more of the thickness of the gas diffusion layer.
[0014]
The above-described fuel cell manufacturing method, fuel cell substrate functioning as a gas diffusion layer, and a representation of the manufacturing method are also effective as the present invention.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 schematically shows a cross-sectional structure of a fuel cell 10 according to an embodiment of the present invention. The fuel cell 10 includes a flat cell 50, and a separator 34 and a separator 36 are provided on both sides of the cell 50. Although only one cell 50 is shown in this example, the fuel cell 10 may be configured by stacking a plurality of cells 50 via the separator 34 or the separator 36. The cell 50 has a solid polymer electrolyte membrane 20, a fuel electrode 22, and an air electrode 24. The fuel electrode 22 and the air electrode 24 may be referred to as “catalyst electrodes”. The fuel electrode 22 has a laminated catalyst layer 26 and a gas diffusion layer 28, and similarly, the air electrode 24 has a laminated catalyst layer 30 and a gas diffusion layer 32. The catalyst layer 26 of the fuel electrode 22 and the catalyst layer 30 of the air electrode 24 are provided so as to face each other with the solid polymer electrolyte membrane 20 interposed therebetween.
[0016]
A gas flow path 38 is provided in the separator 34 provided on the fuel electrode 22 side, and fuel gas is supplied to the cell 50 through the gas flow path 38. Similarly, a gas flow path 40 is also provided in the separator 36 provided on the air electrode 24 side, and an oxidant gas is supplied to the cell 50 through the gas flow path 40. Specifically, during operation of the fuel cell 10, a fuel gas such as hydrogen gas is supplied from the gas flow path 38 to the fuel electrode 22, and an oxidant gas such as air is supplied from the gas flow path 40 to the air electrode 24. . Thereby, a power generation reaction occurs in the cell 50. When hydrogen gas is supplied to the catalyst layer 26 via the gas diffusion layer 28, hydrogen in the gas becomes protons (hydrogen ions), and the protons move through the solid polymer electrolyte membrane 20 toward the air electrode 24. At this time, the emitted electrons move to the external circuit and flow into the air electrode 24 from the external circuit. On the other hand, when air is supplied to the catalyst layer 30 through the gas diffusion layer 32, oxygen in the air combines with protons to become water. As a result, electrons flow from the fuel electrode 22 toward the air electrode 24 in the external circuit, and electric power can be taken out.
[0017]
The solid polymer electrolyte membrane 20 exhibits good ion conductivity in a wet state, and functions as an ion exchange membrane that moves protons between the fuel electrode 22 and the air electrode 24. The solid polymer electrolyte membrane 20 is formed of a solid polymer material such as a fluorine-containing polymer or a non-fluorine polymer. For example, as the fluorine-containing polymer, a sulfonic acid type perfluorocarbon polymer, a polysulfone resin, a phosphonic acid group, or a carboxyl A perfluorocarbon polymer having an acid group can be used, and a sulfonated aromatic polyether ketone, a sulfonated polyether sulfone, or the like can be used as the non-fluorine polymer. Examples of the sulfonic acid type perfluorocarbon polymer include Nafion (manufactured by DuPont: registered trademark) 112.
[0018]
The gas diffusion layer 28 in the fuel electrode 22 and the gas diffusion layer 32 in the air electrode 24 have a function of supplying the supplied hydrogen gas or air to the catalyst layer 26 and the catalyst layer 30. In addition, it has a function of moving charges generated by the power generation reaction to an external circuit and a function of releasing water, unreacted gas, and the like to the outside. The gas diffusion layer 28 and the gas diffusion layer 32 are preferably composed of a porous substrate having electron conductivity, and are composed of, for example, carbon paper, carbon cloth, carbon nonwoven fabric, or the like.
[0019]
The catalyst layer 26 in the fuel electrode 22 and the catalyst layer 30 in the air electrode 24 are porous membranes and are preferably composed of at least an ion exchange resin and carbon particles supporting the catalyst. Examples of the supported catalyst include a mixture of one or more of platinum, ruthenium, rhodium and the like, and alloys thereof. Examples of the carbon particles supporting the catalyst include acetylene black, ketjen black, furnace black, and carbon nanotube.
[0020]
The ion exchange resin functions as a proton conduction path between the catalyst supported on the carbon particles and the solid polymer electrolyte membrane 20. Therefore, the ion exchange resin is required to have proton conductivity. Moreover, in order to diffuse hydrogen and oxygen to the catalyst, a certain degree of gas permeability is required. The ion exchange resin may be formed of the same polymer material as the solid polymer electrolyte membrane 20.
[0021]
Hereinafter, an example of a method for manufacturing the cell 50 will be described. First, in order to produce the fuel electrode 22 and the air electrode 24, a catalyst such as platinum is supported on the carbon particles by using, for example, an impregnation method or a colloid method. Next, catalyst particles are produced by dispersing carbon particles supporting the catalyst and ion exchange resin in a solvent. On the other hand, the gas diffusion layer may be subjected to a water repellent treatment with a fluororesin or the like, or a treatment in which a mixture of carbon particles or fluororesin is applied to the surface or packed inside. The fuel electrode 22 and the air electrode 24 are produced by applying the catalyst ink to, for example, carbon paper serving as a gas diffusion layer, and heating and drying. As the coating method, for example, techniques such as brush coating, spray coating, screen printing, doctor blade coating, and transfer may be used. Subsequently, the solid polymer electrolyte membrane 20 is sandwiched between the catalyst layer 26 of the fuel electrode 22 and the catalyst layer 30 of the air electrode 24, and is joined by hot pressing. Thereby, the cell 50 is produced. When the solid polymer electrolyte membrane 20 or the ion exchange resin in the catalyst layer 26 and the catalyst layer 30 is composed of a polymer material having a softening point or a glass transition, hot pressing is performed at a temperature exceeding the softening temperature or the glass transition temperature. Is preferred.
[0022]
The following example is given as another method for manufacturing the cell 50. The catalyst layer 26 and the catalyst layer 30 may be formed by directly applying the catalyst ink to the solid polymer electrolyte membrane 20 and heating and drying. The coating method may be a technique such as spray coating. Also good. The cell 50 may be manufactured by disposing a gas diffusion layer outside the catalyst layer 26 and the catalyst layer 30 and performing hot pressing. The following example is given as another method for manufacturing the cell 50. The catalyst layer 26 and the catalyst layer 30 may be formed by applying a catalyst ink on a Teflon (registered trademark) sheet and heating and drying. Examples of the application method include spray coating and screen printing. Technology may be used. Subsequently, the catalyst layer 26 and the catalyst layer 30 formed on the Teflon sheet are sandwiched by facing the solid polymer electrolyte membrane 20, and bonded by hot pressing. Thereafter, the Teflon sheet may be peeled off and a gas diffusion layer may be disposed outside the catalyst layer 26 and the catalyst layer 30.
[0023]
In the present embodiment, at least one of the fuel electrode 22 and the air electrode 24 has a gas diffusion layer 28 or gas containing spiral carbon fibers in which a plurality of linear carbon fibers are wound around other carbon fibers. A diffusion layer 32 is provided. Hereinafter, for convenience of explanation , the gas diffusion layer will be described by using the gas diffusion layer 32 in the air electrode 24 as a representative.
[0024]
FIG. 2 shows an example of a helical carbon fiber in which a plurality of straight carbon fibers are wound around another carbon fiber. When the gas diffusion layer 32 is constituted by a woven fabric, a nonwoven fabric, or paper made of a spiral carbon fiber, the electrical conduction in the thickness direction, in addition to the electrical conduction path by the contact of the carbon fiber bundle inside the spiral, An electric conduction path is formed by the carbon fibers wound around the periphery. Thereby, the electrical conductivity in the thickness direction can be improved. In addition, since it has a structure in which a carbon fiber bundle is wound with other carbon fibers, it has strength compared to a hollow coiled carbon fiber, and the outer coiled carbon fiber is crushed and gas diffusible. Occurrence of phenomena such as a decrease, a decrease in strength of the gas diffusion layer, and a decrease in electrical conductivity can be suppressed. In addition, by winding and restraining the carbon fiber bundle with other carbon fibers, the gap between the carbon fibers inside the helix is narrowed and stabilized, so water management such as water absorption, water retention, moisture release, etc. by capillary action. Can be improved.
[0025]
The helical carbon fiber can be produced, for example, by the method described in JP-A-5-247759 or JP-A-10-317243. Japanese Patent Application Laid-Open No. 5-247759 discloses a method for producing a multilayer composite spun yarn having a structure in which a filament yarn is a core and a short fiber bundle A and a short fiber bundle B are wound around the filament yarn. In the embodiment, an example is described in which a polyester wooly yarn is used as the filament yarn, polyester is used as the short fiber bundle A, and cotton is used as the short fiber bundle B. In order to manufacture the helical carbon fiber of the present embodiment, for example, using polyacrylonitrile as the filament yarn and the short fiber bundle A, a two-layer composite spun yarn is manufactured, and a woven fabric, a non-woven fabric, Or after forming paper, it may be baked and carbonized. Japanese Patent Application Laid-Open No. 10-317243 discloses a method of manufacturing a constraining fiber bundle in which a presser thread is wound around a roving fiber bundle in a spiral shape. The helical carbon fiber of the present embodiment is produced by producing a constrained fiber bundle of polyacrylonitrile by the method of this publication, forming a woven fabric, non-woven fabric, or paper from the constrained fiber bundle, and then firing and carbonizing it. Can be manufactured.
[0026]
The gas diffusion layer 32 may be formed of only spiral carbon fibers, or may be formed by mixing spiral carbon fibers and linear carbon fibers. Specifically, the gas diffusion layer 32 is made of a carbon fiber bundle (mixed yarn or mixed fiber) in which only a spiral carbon fiber or a mixture of a spiral carbon fiber and a linear carbon fiber at a predetermined ratio. It may be formed in a woven fabric shape, or may be formed in a nonwoven fabric shape or a paper shape by mixing only a spiral carbon fiber or a mixture of a spiral carbon fiber and a linear carbon fiber at a predetermined ratio. .
[0027]
When forming the gas diffusion layer 32 by forming the helical carbon fiber in a woven fabric shape, the outer diameter (indicated by r in the drawing) of the helical carbon fiber is 50% or more of the thickness of the gas diffusion layer 32. Is preferred. For example, when the thickness of the gas diffusion layer 32 is 180 μm, the outer diameter of the helical carbon fiber is preferably 90 μm or more. At this time, the lamination in the thickness direction of the helical carbon fiber is about two layers, and compared with the gas diffusion layer 32 formed by laminating a large number of linear carbon fibers, the contact resistance is reduced and the electric conductivity in the thickness direction is reduced. Can be improved. The upper limit of the outer diameter of the helical carbon fiber is not particularly limited, but may be, for example, equal to or less than the thickness of the gas diffusion layer 32.
[0028]
The length of the helical carbon fiber in the longitudinal direction (indicated by 1 in the figure) is preferably longer than the thickness of the gas diffusion layer 32. Thereby, when forming the gas diffusion layer 32, the phenomenon that the helical carbon fiber shorter than the thickness is oriented in the thickness direction and breaks through the electrolyte membrane can be suppressed.
[0029]
When forming the gas diffusion layer 32 by forming the helical carbon fiber into a nonwoven fabric or paper shape, the outer diameter (r in the figure) of the helical carbon fiber is 30% or more of the thickness of the gas diffusion layer 32. Is preferred. For example, when the thickness of the gas diffusion layer 32 is 180 μm, the outer diameter of the helical carbon fiber is preferably 60 μm or more. At this time, the thickness direction of the spiral carbon fibers is about three layers, and compared with the gas diffusion layer 32 formed by laminating a large number of linear carbon fibers, the contact resistance is reduced and the electrical conductivity in the thickness direction is improved. Can be made.
[0030]
(Second Embodiment)
In the present embodiment, at least one of the fuel electrode 22 or the air electrode 24 has a gas diffusion layer 28 or gas containing spiral carbon fibers in which the circumference of one linear carbon fiber is wound with another carbon fiber. A diffusion layer 32 is provided. The overall configuration of the fuel cell of the present embodiment is the same as that of the fuel cell 10 of the first embodiment shown in FIG. Hereinafter, as in the first embodiment, the gas diffusion layer will be described by using the gas diffusion layer 32 in the air electrode 24 as a representative.
[0031]
FIG. 3 shows an example of a spiral carbon fiber in which one straight carbon fiber is wound around another carbon fiber. When the gas diffusion layer 32 is composed of a woven fabric, a nonwoven fabric, or paper made of spiral carbon fibers, the spiral carbon fibers are laminated to form a spiral due to the presence of the outer coiled carbon fibers. A void (shown by a in the figure) is formed between the carbon-like carbon fibers. In order to prevent formation of water in the gas diffusion layer 32 and to ensure smooth gas diffusion, the gas diffusion layer 32 is generally water-repellent treated with a fluororesin. There is a possibility that the fluororesin of the coating coats the contact portion between the carbon fibers and hinders electrical conduction. In this Embodiment, since the space | gap a exists between helical carbon fibers, a fluororesin adheres preferentially to the space | gap a by a capillary phenomenon. Thereby, the increase in the contact resistance between the helical carbon fibers due to the adhesion of the fluororesin can be suppressed.
[0032]
The helical carbon fiber of the present embodiment can be manufactured by applying the same method as that of the first embodiment using one thread inside the spiral. The outer diameter of the helical carbon fiber is the same as that in the first embodiment.
[0033]
The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.
[0034]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the fuel cell provided with the gas diffusion layer which implement | achieves a favorable function can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a cross-sectional structure of a fuel cell according to an embodiment.
FIG. 2 is a view showing an example of a helical carbon fiber in which a plurality of straight carbon fibers are wound around another carbon fiber.
FIG. 3 is a diagram showing an example of a spiral carbon fiber in which a circumference of one straight carbon fiber is wound with another carbon fiber.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Fuel cell, 20 ... Solid polymer electrolyte membrane, 22 ... Fuel electrode, 24
... Air electrode, 26 ... Catalyst layer, 28 ... Gas diffusion layer, 30 ... Catalyst layer,
32 ... Gas diffusion layer, 50 ... Cell.

Claims (6)

A fuel cell comprising an electrolyte membrane, and a first electrode and a second electrode provided on the electrolyte membrane,
At least one of the first electrode and the second electrode includes a gas diffusion layer including a spiral carbon fiber in which a carbon fiber is wound around the carbon fiber. A fuel cell comprising an electrolyte membrane, and a first electrode and a second electrode provided on the electrolyte membrane,
At least one of the first electrode and the second electrode includes a gas diffusion layer including a spiral carbon fiber in which a plurality of carbon fibers are wound around the carbon fiber.   3. The fuel cell according to claim 1, wherein the gas diffusion layer is formed by forming the spiral carbon fiber into a woven fabric shape. 4.   The fuel cell according to claim 3, wherein an outer diameter of the helical carbon fiber is 50% or more of a thickness of the gas diffusion layer.   3. The fuel cell according to claim 1, wherein the gas diffusion layer is formed by forming the helical carbon fibers into a nonwoven fabric or a paper.   6. The fuel cell according to claim 5, wherein an outer diameter of the helical carbon fiber is 30% or more of a thickness of the gas diffusion layer.

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