JPH09245800A - Fuel cell and electrode for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve water discharge property of generated water and supply property for an electrolyte layer and ensure gas transmission in a fuel call anode. SOLUTION: An electron base material constituting a cathode 23 is made of carbon cross to which hydrophilic treatment is applied, and a hydrophilic part 60 is formed. The cathode 23 is provided with an electrolyte film side water repellent part 62 on the surface of the side of an electrolyte film and is provided with a gas flow route side water repellent part 64 on the surface of the side of a gas flow route. Part of the generated water generated by means of battery reaction is repelled by the electrolyte film side water resistance part 62 and is pushed back to the electrolyte film, and the electrolyte film is prevented from being dried. The residual generated water is absorbed by the hydrophilic part 60, is guide to the gas flow route side, and evaporates in gas oxide. In addition, gas divergence of the gas oxide is improved by water repellency provided with the electrolyte film side water repellent part 62.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell and an electrode for a fuel cell, and more particularly to a fuel cell and an electrode for a fuel cell provided with an electrode having conductivity and gas permeability.

[0002]

2. Description of the Related Art A fuel cell is a device that directly converts chemical energy of fuel into electrical energy without passing through thermal energy or mechanical energy, and is known as a device capable of obtaining high power generation efficiency. There is. In a fuel cell, a fuel gas containing hydrogen is supplied to an anode, an oxidizing gas containing oxygen is supplied to a cathode, and an electromotive force is obtained by an electrochemical reaction that occurs at both electrodes. The following shows an equation representing an electrochemical reaction occurring in a fuel cell. The equation (1) shows the reaction at the anode, the equation (2) shows the reaction at the cathode, and the equation (3) shows the reaction occurring in the entire battery.

H ₂ → 2H ⁺ + 2e ⁻ (1) (1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2) H ₂ + (1/2) O ₂ → H ₂ O (3) )

In order for such a cell reaction to proceed continuously and the fuel cell to generate power stably, it is necessary to continue to efficiently supply the fuel gas and the oxidizing gas to each electrode.
Therefore, as a fuel cell electrode, an electrode plate made of a carbon-based material having gas diffusivity and conductivity has been conventionally used. Specifically, the electrodes are formed of carbon cloth woven from threads made of carbon fibers, carbon felt or carbon paper which is also made of carbon fibers.

In a fuel cell, when power is generated by the electrochemical reaction represented by the above equation, water is produced at the cathode as shown in equation (2). If the water thus generated stays at the cathode as it is, it blocks the gas diffusion path, hinders the gas diffusion at the electrodes, and lowers the cell reaction. Therefore, it is necessary to quickly drain the water generated by the battery reaction from the electrodes.

Therefore, conventionally, water repellent carbon was prepared by mixing carbon powder and polytetrafluoroethylene (trade name: Teflon, hereinafter referred to as PTFE), and the water repellent carbon was pasted into both sides of the carbon cloth. It was used as an electrode after it was applied to and fired to make the surface of the carbon cloth water repellent. In the electrode thus manufactured, the generated water is repelled by the water-repellent carbon applied to the carbon cloth, so that the generated water is easily discharged.
Further, the water repellent carbon repels water on the surface of the electrode, which improves gas diffusivity. A solid polymer electrolyte fuel cell is manufactured by using this electrode for both electrodes, and the fuel cell is operated according to the conventional condition shown in FIG.
As shown in the graph, the stable power generation is performed at a high voltage. The electrodes used here are coated with water-repellent carbon on both surfaces of both the anode and the cathode.

[0007]

However, FIG.
When the fuel cell is operated under the conventional conditions shown in (1), 65% of the power generated by the fuel cell consumes energy for operating the fuel cell, which is difficult to employ. That is, depending on the fuel cell,
When generating kW of electric power, under the above-mentioned conventional conditions, it is necessary to add 5 to humidify the fuel gas and the oxidizing gas supplied to each electrode.
kW is consumed, and 8 kW is consumed to pressurize the oxidizing gas supplied to the anode. In order to improve power generation efficiency, it is necessary to reduce the amount of power consumed during power generation.

First, the humidification of gas and the power consumed by it will be described. At the anode, a proton is generated by the reaction represented by the formula (1), and the proton moves in the electrolyte membrane toward the cathode in a state of being bound with water molecules. As described above, since water is consumed on the anode side of the electrolyte membrane, it is necessary to prevent the electrolyte membrane from drying by humidifying the fuel gas. In the reaction at the cathode, water is generated as in the equation (2), but since the oxidizing gas supplied to the cathode is pressurized, the surface of the electrolyte membrane may be partially dried. Therefore, conventionally, the oxidizing gas is actively humidified together with the fuel gas.
The fuel cell was operated under the conventional conditions shown in FIG. In order to humidify the fuel gas and the oxidizing gas in this way, when generating 20 kW by the fuel cell, about 5 kW of electric power is consumed. Here, we stopped actively humidifying the fuel gas and oxidizing gas as described above,
If energy is not consumed for humidifying the gas, the oxidizing gas has a humidity of 0%, and the fuel gas is humidified when the raw fuel methanol is steam-reformed to generate the fuel gas. Humidity is about 60%.

Next, the pressurization of the oxidizing gas and the power consumed by it will be described. In a fuel cell, a cell reaction, which is a chemical reaction, is promoted by increasing the pressure of the gas supplied to each electrode. Therefore, an oxidizing gas such as air is pressurized by a pump or the like. FIG. 14 shows a fuel cell output of 2
It is a graph which shows the magnitude | size of the electric power consumed by pressurization, when it sets it as 0 kW. As shown in FIG. 14, the amount of electric power consumed by pressurization is determined by the pressurizing pressure and the excess air ratio. The excess air ratio refers to the ratio of the amount of air actually supplied to the amount of air theoretically required to operate the fuel cell and obtain a predetermined electric power. Normally, it is necessary to supply an excessive amount of air when performing power generation by a fuel cell. If only the theoretically required amount of air is supplied, the concentration of oxygen supplied to the terminal portion inside the fuel cell becomes low, and the efficiency of the cell reaction decreases. Therefore, an excessive amount of air is supplied to the fuel cell so that a sufficient amount of oxygen is also supplied to the terminal portion.

Under the conventional conditions, the supply pressure is 0.15 MPa.
And the excess air ratio was 6. Under such conditions, when generating 20 kW by the fuel cell, about 8 kW of electric power is consumed to drive the pressurizing pump. As shown in FIG. 14, if the excess air ratio or the supply pressure is lowered, the power consumption by the pump is reduced, but the pressure of the oxidizing gas cannot be lowered so much to maintain the power generation efficiency. Here, when the supply pressure is set to 0.15 MPa and the pressurization condition is set such that the electric power consumed by the pressurization pump is 10% of the power generation amount, the excess air ratio becomes 2 as in the conventional condition. FIG. 13 shows conditions under which the power consumption by pressurization is 10% of the power generation and the humidification of the gas is not actively performed. The supply pressure and excess rate of the fuel gas may be set in consideration of the balance with the oxidizing gas, and may be adjusted by a pressure adjusting valve provided in the fuel gas supply path connecting the reformer and the fuel cell.

When the fuel cell is operated according to the setting conditions of FIG. 13 set in this way, in order to confirm whether or not the fuel cell can actually be operated with an efficiency of 10%, the water-repellent carbon A polymer electrolyte fuel cell was prepared by using an electrode having the surface coated with (a conventionally used electrode). When the fuel cell is operated according to the set conditions of FIG. 13, as shown by the graph of reference numeral b in FIG. 15, the high voltage is not obtained and the voltage is reduced in a short time with the passage of time. It will cause a descent.

It is considered that the reason why the voltage does not rise during the power generation of the fuel cell is that the wetting of the electrolyte membrane is insufficient and the internal resistance of the fuel cell is large. In addition, the voltage drop occurs immediately because the water generated by the battery reaction stays inside the electrode and blocks the gas flow path, and the oxidizing gas is not sufficiently supplied to the electrode, resulting in poor operating efficiency. It is thought to be due to the decrease. Under the above set conditions, in particular, the rate of humidification of the fuel gas is low and the flow rate of the gas is small, so it is considered that the water supply to the anode side is not sufficient. In addition, on the cathode side, even if water is generated by the cell reaction, the oxidizing gas is not humidified at all, so there is a possibility that the electrolyte membrane will have a partial water shortage and the resistance value will increase. There is. Further, on the cathode side, it is considered that the generated water is not sufficiently drained due to the small flow rate of the oxidizing gas and the gas flow path is blocked. Therefore, in order to operate the fuel cell under the above set conditions, each electrode is provided with water supply for improving the gas diffusivity and keeping the electrolyte membrane in a sufficiently wet state, and the cathode is drained of the produced water. It is necessary to improve sex.

As a method for improving such water supply, drainage, and gas diffusibility, a method of weaving a warp yarn made of hydrophilic carbon fiber and a weft yarn made of water repellent carbon fiber to form an electrode Have been proposed (for example, JP-A-7-105957). In such a method, it is said that the hydrophilic carbon fibers remove generated water and supply makeup water, and the water-repellent carbon fibers repel water to supply and discharge gas.

However, in such a method, the gas is supplied and discharged by the water-repellent thread woven in parallel with the electrode surface, and the gas flow path in the electrode is parallel with the electrode surface, so that the gas permeation is prevented. The path will be longer. From the viewpoint of gas permeation efficiency, it is desirable that the gas permeation path be short. The result of power generation by a fuel cell produced by using an electrode formed by weaving a warp yarn made of hydrophilic carbon fiber and a weft yarn made of water-repellent carbon fiber is shown in FIG. The state of power generation is improved as compared with the case where an electrode coated with water repellent carbon is used, but under the condition that the power consumption for operation is suppressed to 10%, even if such an electrode is used, an electrolyte membrane is used. It is considered that it may be difficult to maintain the gas diffusivity in the electrode to a sufficient degree while sufficiently maintaining the wet state of.

The fuel cell and the fuel cell electrode of the present invention solve these problems, improve the drainage of the produced water in the cathode and the water supply to the electrolyte layer, and the water supply in the anode, and the gas permeation in the electrode. It was made with the aim of ensuring the security and adopted the following structure.

[0016]

The fuel cell of the present invention is a fuel cell comprising an electrolyte layer and a positive electrode and a negative electrode sandwiching the electrolyte layer. The positive electrode is subjected to hydrophilic treatment. The gist is that a water repellent layer having a water repellent substance is formed on at least the surface of the applied electrode base material on the side of the electrolyte layer.

According to the fuel cell of the present invention as described above, the water droplets generated on the surface of the electrolyte layer on the positive electrode side are absorbed by the electrode base material subjected to the hydrophilic treatment. The generated water absorbed by the electrode base material is guided to the surface of the electrode and vaporized in the gas supplied to the fuel cell, and is discharged outside the fuel cell together with the gas.
As described above, since the generated water is quickly discharged from the positive electrode, the generated water does not stay in the electrode and block the gas flow path. Further, in the positive electrode, water is repelled by the water repellent layer formed on the surface of the electrolyte layer side, so that the generated water is unlikely to block the gas flow path, and the gas involved in the battery reaction flows efficiently. be able to.

In the above-described fuel cell of the present invention, the positive electrode has the water-repellent layer formed on both sides thereof using a water-repellent substance having no conductivity, and the water-repellent layer formed on the side in contact with the electrolyte layer. The water layer may contain a greater amount of the water repellent substance than the water repellent layer formed on the other surface.

In the fuel cell having such a structure, in the positive electrode having the water-repellent layer formed on both surfaces, the water-repellent layer formed on the side in contact with the electrolyte layer is larger than the water-repellent layer formed on the other surface. Since it contains the water-repellent substance, the water-repellent layer formed on the side in contact with the electrolyte layer exhibits strong water repellency. Here, since the water-repellent substance does not have conductivity, simply increasing the amount of the water-repellent substance to enhance the water-repellent property will increase the resistance value of the electrode, which will rather deteriorate the battery performance. Therefore, while suppressing the total amount of the water-repellent substance contained in both water-repellent layers, the amount of the water-repellent substance contained in each water-repellent layer is distributed as described above to enhance the water repellency of the desired surface. The increase in the resistance value of the electrode can be suppressed.

With this structure, the excess water produced in the electrolyte membrane is repelled by the water-repellent layer provided on the surface of the positive electrode that is in contact with the electrolyte layer, and is pushed back into the electrolyte membrane. Since the non-humidified pressurized air is supplied to the partially dried region, the electrolyte membrane can be prevented from drying. Here, since the water-repellent layer formed on the surface in contact with the electrolyte layer contains a large amount of water-repellent substance, the generated water generated in the electrolyte layer is effectively pushed back, and the wet state of the electrolyte membrane is sufficiently maintained. be able to. Further, since the water-repellent layer is formed on the surface of the positive electrode opposite to the surface in contact with the electrolyte layer, water can be repelled even on the surface on the opposite side. Therefore, the generated water that is guided to the electrode surface and remains without being evaporated does not form a water film on the electrode surface and hinders gas diffusion, and excess generated water is easily repelled and drained. .

In the fuel cell of the present invention, the water-repellent layer is formed by mixing the water-repellent substance and carbon powder having a hydrophilic functional group content of not more than a predetermined amount, and then the electrode substrate. It may be configured to be applied to the surface of the material.

In the fuel cell having such a structure, the water repellent layer is formed by coating the surface of the electrode with a mixture of the water repellent substance and carbon powder. Is also affected by. Here, since the carbon powder forming the water repellent layer has a content of the hydrophilic functional group of not more than a predetermined amount, the water repellency of the water repellent layer is further improved. Therefore, in the surface of the positive electrode that is in contact with the electrolyte layer, the generated water is more likely to be pushed back, and the wet state of the electrolyte layer can be maintained well. Further, by improving the water repellency in this way, the gas involved in the battery reaction also diffuses efficiently.

Further, in the fuel cell of the present invention, the negative electrode may be composed of an electrode base material subjected to a hydrophilic treatment. In such a case, in addition to the effects of the present invention described above, the electrode base material forming the negative electrode is also subjected to the hydrophilic treatment, so that the water supply on the negative electrode side is improved. The fuel gas supplied to the negative electrode side is humidified in an amount according to the power generation conditions, and the water vapor in the fuel gas is quickly absorbed by the electrode base material subjected to the hydrophilic treatment. The water vapor absorbed by the negative electrode is supplied to the electrolyte layer as needed, so that the surface of the electrolyte layer on the negative electrode side can be prevented from drying. In this way, the water vapor in the fuel gas can be efficiently guided to the electrolyte layer, so that the amount of humidification of the fuel gas supplied to the negative electrode side can be suppressed.

The fuel cell electrode of the present invention is a fuel cell electrode having a predetermined conductivity and gas permeability, and at least one surface of the hydrophilically treated electrode substrate is provided with a water-repellent substance. The gist is that a water repellent layer is formed.

The fuel cell electrode of the present invention constructed as described above has a predetermined conductivity and gas permeability, and the electrode base material forming the electrode is subjected to hydrophilic treatment to exhibit hydrophilicity,
A water-repellent layer including a water-repellent substance is formed on at least one surface of the electrode base material. When a fuel cell is assembled using such a fuel cell electrode as a positive electrode to generate electricity, the generated electromotive force is transmitted by a predetermined conductivity and the supplied gas is efficiently transmitted by a predetermined gas permeability. Can spread well. Further, due to the hydrophilicity of the electrode base material, excess generated water generated in the battery reaction can be guided to the electrode surface and evaporated. Furthermore, the water repellency of the water repellent layer formed on the electrode surface improves the diffusivity of gas and repels the generated water to accelerate drainage.

In the fuel cell electrode of the present invention as described above, the water repellent layer is formed on both surfaces of the electrode base material using a substance having no conductivity, and the water repellent layer is formed on both surfaces of the electrode base material. Further, the respective water repellent layers may contain different amounts of the water repellent substance.

When such a fuel cell electrode is used as a positive electrode and a fuel cell is assembled so that the side containing a large amount of the water-repellent substance is in contact with the electrolyte membrane to generate electricity, the water produced by the cell reaction is repelled. Since the water repellent layer containing a large amount of the aqueous substance is effectively repelled and pushed back to the electrolyte layer, the electrolyte layer can be prevented from being dried. Further, the water-repellent layer formed on the side not in contact with the electrolyte layer can quickly drain the excess water produced by evaporating and remaining on the electrode surface.

In the fuel cell electrode of the present invention,
The water-repellent layer may be formed by mixing the water-repellent substance and carbon powder having a hydrophilic functional group content of a predetermined amount or less and then applying the mixture on the surface of the electrode base material.

In the fuel cell electrode having such a structure, the water repellent layer is formed by coating the surface of the electrode with a mixture of the water repellent substance and carbon powder. It is also affected by carbon powder. Here, since the carbon powder forming the water repellent layer has a content of the hydrophilic functional group of not more than a predetermined amount, the water repellency of the water repellent layer is further improved. Therefore, when a fuel cell is assembled using such a fuel cell electrode as a positive electrode to generate electric power, the water repellency is improved and the gas involved in the cell reaction is efficiently diffused. Further, when there is a difference in water repellency on both sides of such a fuel cell electrode, if the fuel cell is assembled so that the side having strong water repellency is the electrolyte layer side,
On the surface of the positive electrode that is in contact with the electrolyte layer, the generated water is more likely to be pushed back, and the wet state of the electrolyte layer can be maintained well.

The fuel cell system of the present invention comprises a fuel cell comprising an electrolyte layer and a positive electrode and a negative electrode sandwiching the electrolyte layer, and fuel gas and air are fed to the fuel cell at a predetermined pressure and a predetermined excess air ratio. In a fuel cell system including a gas supply means for supplying, a positive electrode of the fuel cell has a water-repellent layer having a water-repellent substance on at least the surface of the electrode base material subjected to a hydrophilic treatment on the electrolyte layer side. Formed,
The excess air ratio of the air supplied by the gas supply means is 3 or less.

The fuel cell system of the present invention configured as described above comprises an electrolyte layer and a positive electrode and a negative electrode sandwiching the electrolyte layer, and the positive electrode is at least an electrode base material subjected to hydrophilic treatment. Power generation is performed by a fuel cell having a water-repellent layer having a water-repellent substance formed on the surface of the electrolyte layer side. When power is generated in the fuel cell system, the gas supply means supplies the fuel gas and the air to the fuel cell at a predetermined pressure and a predetermined excess air ratio. At this time, the gas supply unit supplies air so that the excess air ratio becomes 3 or less.

According to the fuel cell system of the present invention as described above, when power is generated by the fuel cell, excess water produced by the cell reaction is absorbed by the electrode base of the positive electrode which has been subjected to the hydrophilic treatment. Since it is guided to the electrode surface and evaporates into the oxidizing gas, it can be quickly drained. Further, due to the water repellency of the water repellent layer formed on the electrode surface, the diffusibility of gas in the positive electrode is improved and the generated water is repelled to promote drainage. Furthermore, since the air supplied by the gas supply means has an excess air ratio of 3 or less, a large amount of energy is not consumed to supply the air to the fuel cell.

[0033]

Other Embodiments of the Invention The present invention can also take the following other embodiments. That is, as a first other aspect, in the above-described configuration of the present invention, the electrode base material may be made of carbon.

In such an embodiment, the hydrophilic treatment is applied to the carbon electrode base material, and the water repellent layer is formed on the surface of the carbonized electrode base material, if necessary. . Therefore, the present invention can be applied as it is to an electrode base material made of carbon which has been conventionally used as an electrode base material in a polymer electrolyte fuel cell, a phosphoric acid fuel cell or the like. Conventionally, carbon has been assumed to have a predetermined hydrophilicity, but by further subjecting this carbon to the above-mentioned hydrophilic treatment, the positive electrode has an increased absorption of the generated water and improved drainage. However, in the negative electrode, the water retention of the water vapor supplied together with the fuel gas is improved, and the water supply to the electrolyte layer is enhanced.

As a second other aspect, in the above-mentioned constitution of the present invention, the water-repellent layer has a content of the water-repellent substance and an acidic functional group of 0.3 × 10 ⁻⁴ (mol). /
g) After being mixed with the following carbon powder, it may be applied on the surface of the electrode base material.

In such an embodiment, since the water repellent layer is formed by coating the surface of the electrode with a mixture of the water repellent substance and carbon powder, the water repellent property of the water repellent layer depends on the carbon powder. Is also affected. Here, the carbon powder forming the water repellent layer has an acid functional group content of 0.3 ×.
Although it is 10 ^-4 (mol / g) or less, since the acidic functional group contains a major hydrophilic functional group, the carbon powder having the above acidic functional group content has the above acidic functional group content. Exhibits stronger water repellency than carbon powders that exceed. Therefore, the water repellency of the water repellent layer is further improved. In the water repellent layer on the side of the anode that is in contact with the electrolyte layer, the generated water is more easily pushed back, and the wet state of the electrolyte layer is maintained in a good condition. Further, the water repellency is improved, so that the gas involved in the battery reaction is efficiently diffused.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION In order to further clarify the structure and operation of the present invention described above, the embodiments of the present invention will be described below based on Examples. FIG. 1 is a schematic diagram showing the movement of generated water and oxidizing gas at a cathode 23 in a fuel cell 20 which is a preferred embodiment of the present invention, and FIG. 2 is a fuel provided with the fuel cell 20. Battery system 30
3 is a block diagram showing an outline of FIG. For convenience of explanation,
First, the configuration of the fuel cell system 30 will be described with reference to FIG. The fuel cell system 30 includes a methanol tank 31, a water tank 32, a reformer 3 in addition to the fuel cell 20.
4. The pump 36 is a main component. Hereinafter, each part of the fuel cell system 30 will be described.

The fuel cell 20 is a solid polymer electrolyte type fuel cell, and has a stack structure in which a plurality of unit cells 28, which are constituent units, are laminated. FIG. 3 is a cross-sectional view illustrating the configuration of the single cell 28 that constitutes the fuel cell 20. The unit cell 28 is composed of an electrolyte membrane 21, an anode 22 and a cathode 23, and separators 24 and 25.

The anode 22 and the cathode 23 are gas diffusion electrodes having a sandwich structure with the electrolyte membrane 21 sandwiched from both sides. The separators 24 and 25 sandwich the sandwich structure from both sides, and
A flow path for the fuel gas and the oxidizing gas is formed between the cathode 2 and the cathode 23. A fuel gas passage 24P is formed between the anode 22 and the separator 24, and an oxidizing gas passage 25P is formed between the cathode 23 and the separator 25.
Are formed. In FIG. 3, the separators 24 and 25 each have a flow path formed on only one surface, but in reality, ribs are formed on both surfaces, and one surface forms a fuel gas flow path 24P with the anode 22. On the other side, the oxidizing gas flow channel 25P is formed between the cathode 23 and the cathode 23 of the adjacent single cell.
To form As described above, the separators 24 and 25 form a gas flow path with the gas diffusion electrode and also serve to separate the flows of the fuel gas and the oxidizing gas between the adjacent single cells. Of course, when the unit cells 28 are stacked to form a stack structure, the two separators located at both ends of the stack structure have ribs formed only on one surface in contact with the gas diffusion electrode.

Here, the electrolyte membrane 21 is a proton-conducting ion exchange membrane formed of a solid polymer material, for example, a fluorine resin, and exhibits good electric conductivity in a wet state. In this embodiment, a Nafion membrane (manufactured by DuPont) is used.
It was used. The surface of the electrolyte membrane 21 is coated with platinum as a catalyst or an alloy of platinum and another metal. As a method of applying the catalyst, a carbon powder supporting platinum or an alloy composed of platinum and another metal is prepared, and the carbon powder supporting the catalyst is dispersed in an appropriate organic solvent, and an electrolytic solution (eg, Aldrich Chemi) is used.
Calf Corporation, Nafion Solution) is added in an appropriate amount to form a paste, and the sheet obtained by forming the paste into a film is pressed onto the electrolyte membrane 21.

The anode 22 and the cathode 23 are both made of carbon cloth (GF-20-P7, plain weave manufactured by Nippon Carbon Co., Ltd.) woven with threads made of carbon fibers. Here, the anode 22 and the cathode 23 are subjected to hydrophilic treatment at their bases, and a water-repellent portion provided with a water-repellent substance is formed on the surface thereof. These configurations are essential parts of the present invention. This will be described later in detail. In the present embodiment, the anode 22 and the cathode 23 are formed of carbon cloth, but a configuration formed of carbon paper or carbon felt made of carbon fiber is also suitable.

In this embodiment, as described above, the carbon powder carrying the catalyst was prepared, and the sheet obtained by film-forming the paste containing the carbon powder was pressed onto the electrolyte membrane 21. By using such a method, a small amount of catalyst can be uniformly pressure-bonded on the electrolyte membrane 21, and in the fuel cell 20 including such an electrolyte membrane 21, an effective catalytic effect can be obtained with a small amount of catalyst. . Alternatively, the above catalyst-supporting carbon may be kneaded into the anode 22 and the cathode 23 made of carbon cloth. The surface on which the catalyst-supporting carbon is kneaded is, of course, the surface on the side in contact with the electrolyte membrane 21.

The separators 24 and 25 are formed of a gas impermeable conductive member, for example, dense carbon that is made gas impermeable by compressing carbon. Separator 2
Nos. 4 and 25 have a plurality of ribs arranged in parallel on both surfaces thereof. As described above, the fuel gas flow path 24P is formed with the surface of the anode 22, and the cathode 23 of the adjacent single cell 23 is formed. An oxidizing gas flow path 25P is formed with the surface of the. Here, the ribs formed on the surface of each separator need not be formed in parallel on both surfaces, and may be at a predetermined angle such as perpendicular to each surface. The ribs do not have to be parallel grooves, but may be any as long as a fuel gas or an oxidizing gas can be supplied to the gas diffusion electrode.

The configuration of the single cell 28, which is the basic structure of the fuel cell 20, has been described above. When the fuel cell 20 is actually assembled, the separator 24, the anode 2
2. A plurality of sets of single cells 28, which are composed of the electrolyte membrane 21, the cathode 23, and the separator 25 in this order, are stacked (75 sets in this embodiment), and a collector plate formed of dense carbon or copper plate on both ends thereof. A stack structure is formed by arranging 26 and 27.

The reformer 34 receives supply of methanol and water from the methanol tank 31 and the water tank 32. In the reformer 34, the supplied methanol is used as a raw fuel for reforming by a steam reforming method to generate a hydrogen-rich fuel gas. The reforming reaction performed in the reformer 34 is shown below.

CH ₃ OH → CO + 2H ₂ (4) CO + H ₂ O → CO ₂ + H ₂ (5) CH ₃ OH + H ₂ O → CO ₂ + 3H ₂ (6)

In the reforming reaction of methanol carried out in the reformer 34, the decomposition reaction of methanol represented by the formula (4) and the shift reaction of carbon monoxide represented by the formula (5) simultaneously proceed, and Then, the reaction of the equation (6) occurs. Such a reforming reaction is an endothermic reaction as a whole. The generated hydrogen-rich fuel gas is supplied to the fuel cell 20 through the fuel supply passage 38, and in each fuel cell 20, in each single cell 28, it is guided to the fuel gas flow path 24P and is guided to the anode 22.
In the battery reaction in. When fuel gas is generated by the above-described steam reforming in the reformer 34 of the present embodiment using methanol as a raw fuel, steam in an amount more than the amount necessary for the reforming reaction is supplied in the reformer 34. The fuel gas transmitted to the No. 20 has a humidity of about 60%.

The pump 36 pressurizes and supplies the air taken in from the outside to the fuel cell 12. The air taken in by the pump 36 and pressurized is supplied to the fuel cell 20 through the air supply passage 39, and in the fuel cell 20, each single cell 2 is supplied.
At 8, the gas is introduced into the oxidizing gas flow path 25P and is used for the cell reaction in the cathode 23. In general, in a fuel cell, the reaction speed increases as the pressure of the gas supplied to both electrodes increases, so that the cell performance improves. Therefore, the air supplied to the cathode 23 is pressurized by the pump 36 in this manner. The pressure of the fuel gas supplied to the anode 22 can be easily adjusted by controlling the open state of the pressure regulating valve 37 provided in the fuel supply passage 38 described above. Further, in the present embodiment, the air supplied to the cathode 23 by the pump 36 is not humidified according to the above-mentioned setting conditions of FIG.

In the fuel cell system 30 including the fuel cell 20 of this embodiment, the fuel exhaust gas after being used for the cell reaction at the anode 22 and a part of the air compressed by the pump 36 are reformed. Is supplied to the container 34. As described above, since the reforming reaction in the reformer 34 is an endothermic reaction and requires external heat supply, a burner (not shown) is provided inside the reformer 34 for heating. The fuel gas and compressed air are used for the combustion of this burner. The spent fuel exhaust gas is guided to the reformer 34 by the exhaust gas passage 41, and the compressed air is guided to the reformer 34 by the branch air passage 40 branched from the air supply passage 39. The hydrogen remaining in the fuel exhaust gas and the oxygen in the compressed air are used for burner combustion and supply the heat required for the reforming reaction.

The configuration of the fuel cell system 30 including the fuel cell 20 of this embodiment has been described above.
The structure of the electrode corresponding to the main part of the present invention will be described in detail. The cathode 23, which is a positive electrode of the fuel cell 20, is a gas diffusion electrode made of carbon cloth as described above. In this example, the cathode 23 was subjected to hydrophilic treatment for the purpose of improving the drainage of the generated water in the cathode 23. The hydrophilic treatment of the cathode 23 was performed by immersing the carbon cloth used as the cathode 23 in a solution containing a hydrophilic treatment agent. Si as a hydrophilic treatment agent
O ₂ was adopted. The amount of the hydrophilic treatment agent attached to the carbon cloth can be adjusted by the concentration of the solution containing the hydrophilic treatment agent (Atron NSi-500 manufactured by Nisso Kasei Co., Ltd.). If the hydrophilic treatment agent to be attached is increased, the drainage property of the cathode 23 will be improved, but since SiO ₂ has no conductivity, the resistance value of the cathode 23 will be increased, which will rather reduce the battery performance. Therefore, we investigated how much hydrophilicity is possible within a range that does not deteriorate the battery performance.

The method for evaluating the drainage property of the gas diffusion electrode will be described below. FIG. 4 is a schematic diagram showing the configuration of an evaporation rate measuring device 50 used for investigating the drainage property of the gas diffusion electrode 58 subjected to the hydrophilic treatment.
Gas diffusion electrode 58 installed in evaporation rate measuring device 50
Has its one surface in contact with water stored in the water tank 51, and its other surface in contact with a nitrogen flow path 56 supplied with nitrogen from a nitrogen cylinder 52 provided outside. The water in the water tank 51 communicates with the water level gauge 54, and a change in the amount of water in the water tank 51 is observed as a change in the water level in the water level gauge 54. A heater 55 is provided in the evaporation rate measuring device 50 to keep the internal temperature of the evaporation rate measuring device 50 at a predetermined temperature corresponding to the operating temperature of the fuel cell. Here, 75
It was decided to keep it at ℃. A flow rate adjusting unit 57 is provided between the nitrogen cylinder 52 and the nitrogen channel 56, and the nitrogen channel 5
The flow rate of nitrogen gas supplied to No. 6 can be adjusted.
The amount of nitrogen gas supplied to the surface 58 of the gas diffusion electrode in the nitrogen flow path 56 corresponds to the excess air ratio during fuel cell operation, and the fuel at each excess air ratio is adjusted by adjusting the flow rate adjusting unit 57. The state of the gas diffusion electrode in the battery can be reproduced. However, for convenience of the experiment, the pressure at the time of measurement was atmospheric pressure.

As shown in FIG. 4, when the evaporation rate measuring device 50 is assembled and the inside of the device is kept at the above predetermined temperature, the water tank 51
The water stored in is gradually vaporized, diffuses in the gas diffusion electrode 58, reaches the nitrogen flow path 56, and is discharged to the outside together with the nitrogen gas. Therefore, by measuring the water level of the water level gauge 54 every predetermined time, the amount of water evaporated through the gas diffusion electrode can be known. As shown in FIG. 5, by obtaining the slope of the graph with the horizontal axis as the measurement time and the vertical axis as the amount of evaporated water, the evaporation rate specific to each gas diffusion electrode can be calculated. In this example, the evaporation rate thus examined was used as a measure of the drainage property of the gas diffusion electrode.

FIG. 6 shows the results of comparing the gas diffusivities using the evaporation rate measuring device 50 for the gas diffusion electrodes in which the amount of SiO ₂ to be deposited is changed by changing the treatment time when performing the hydrophilic treatment. Represent. Fuel cell 20
The target is to operate under the set conditions of FIG. 13, but in the case of the excess air ratio 2 according to the set conditions, the S added to the weight of the gas diffusion electrode subjected to the hydrophilic treatment is adhered.
It can be seen that when the ratio of iO ₂ amount is 0.5% or more, the required drainage amount is satisfied. Here, the required drainage is
When the fuel cell generates power at a predetermined output, the amount of water molecules generated on the cathode 23 side of the electrolyte membrane 21 and the amount of water molecules inside the electrolyte membrane 21 that move from the anode 22 side to the cathode 23 side together with the protons. It is the amount calculated based on the sum with the amount of incoming water molecules.

On the other hand, when the relationship between the amount of deposited SiO ₂ and the resistance value of the gas diffusion electrode was examined, as shown in FIG. 7, the gas diffusion ratio which was conventionally used was up to 0.5% of SiO _2. It was found that the resistance value did not change much from that of the electrode, but the resistance value rapidly increased when SiO ₂ was further deposited. From the above results, in this embodiment, the S
The cathode 23 was produced with the amount of iO _{2 set} to 0.5% of the weight of the gas diffusion electrode.

At the time of manufacturing the cathode 23, the prepared carbon cloth is subjected to the above-mentioned hydrophilic treatment to adhere SiO ₂ of 0.5% of the weight of the carbon cloth, and further, the gas diffusion electrode which has been conventionally used. Water-repellent carbon was applied in the same manner as in. The water-repellent carbon is produced and applied as follows. First, carbon powder (furnace black, manufactured by Cabot Co., Ltd., trade name VALCAN XC72) is used as a water repellent substance such as polytetrafluoroethylene (trade name Teflon, hereinafter referred to as PTFE) and polyethylene glycol mono-P-isooctylphenyl ether ( Below, T
It is suspended in water and mixed well with a dispersant such as Ritton X-100). At this time, PTFE and carbon powder were mixed in equal amounts. The carbon powder having PTFE adhering to its surface is separated from water by suction filtration or pressure filtration of this suspension.

At this point, the water-repellent carbon may be produced by treating the carbon powder having PTFE adhered to its surface at about 280 ° C. to evaporate the dispersant and the like, but this step can be omitted. . Hereinafter, the mixture of carbon powder and PTFE prepared for coating on the surface of the carbon cloth, including those obtained by omitting the baking step, will be referred to as water-repellent carbon. The water-repellent carbon thus produced is suspended in ethanol, uniformly dispersed by ultrasonic treatment or the like, and then applied to the surface of the carbon cloth. Water-repellent carbon is 4 mg / cm on both sides of the carbon cloth, excluding the dispersant.
² was applied. After applying the water-repellent carbon, the carbon cloth is fired at about 320 ° C. By this firing process, P
TEF is bound to the surrounding carbon, and the ethanol and dispersant are evaporated to complete the cathode 23. Even when the water-repellent carbon is not baked before applying the water-repellent carbon to the carbon cloth, the dispersant can be evaporated in this way by finally performing the baking.

The fuel cell 20 was assembled using the cathode 23 thus manufactured, and the constant current discharge result of 1 A / cm ² when power generation was performed according to the set conditions of FIG. 13 is shown in FIG. Show. The carbon cloth is subjected to a hydrophilic treatment in which 0.5% by weight of SiO ² is adhered, and then the above water-repellent carbon is applied to both surfaces of 4 mg / cm 2.
^When the cathode 23 applied at a ratio of ² is used, when the conventional cathode not subjected to the hydrophilic treatment is used (graph b), the cathode in which the hydrophilic warp yarn and the hydrophobic weft yarn described above are woven is used. As compared with the case (graph c), a high voltage could be stably obtained.

The movement of the produced water and the oxidizing gas at the cathode 23 in the fuel cell 20 of this embodiment has already been shown in FIG. The cathode 23 has a hydrophilic portion 60 formed by hydrophilically treating carbon cloth, and an electrolyte membrane-side water repellent portion 6 formed by coating water repellent carbon on the surface of the hydrophilic portion 60 on the electrolyte membrane side.
2 and a gas channel side water repellent portion 64 which is also formed by applying water repellent carbon to the surface of the hydrophilic portion 60 on the gas channel side.

According to the fuel cell 20 of this embodiment, since the electrode base material forming the cathode 23 is subjected to the hydrophilic treatment to form the hydrophilic portion 60, the water produced by the cell reaction on the cathode 23 side is not generated. , The hydrophilic portion 60 is easily absorbed, and passes through the gas diffusion electrode to form the oxidizing gas flow path 25P.
It is effectively drained by transpiration to the side. As a result, the generated water does not remain in the cathode 23 and condense to block the gas passage. Therefore, it is possible to prevent the battery reaction from decreasing due to the lack of gas, and it is possible to output a stable voltage. Further, according to the fuel cell 20 of this embodiment, since the electrolyte membrane-side water repellent portion 62 formed by applying water repellent carbon to the surface of the cathode 23 on the side of the electrolyte membrane 21 is formed, a cell reaction occurs. It is possible to repel the generated water and push it back to the electrolyte layer 21. In this way, the generated water is passed through the electrolyte membrane 2
By pushing back to 1, it becomes easier to keep the wet state of the electrolyte membrane 21, and it is possible to prevent an increase in battery resistance due to drying of the electrolyte membrane 21. Further, the water repellent portion 64 on the gas flow path side
By forming the, it is possible to prevent the generated water remaining after being evaporated from remaining on the electrode surface and hindering gas diffusion.

In this embodiment, SiO _{2 is} used as the hydrophilic treatment agent.
In addition to these, TiO ₂ , In ₂ O ₃ , Zr
O ₂ , Ta ₂ O ₅ or the like can be used. The hydrophilic treatment agent thus attached to the electrode base material may be selected from those that do not interfere with the operation of the fuel cell 20 and can withstand the conditions of the manufacturing process of the cathode 23 and the operating conditions of the fuel cell 20. In particular, when the hydrophilic substance does not have conductivity or has an effect of inhibiting the battery reaction, when the hydrophilic agent in an amount necessary for making the electrode base material hydrophilic is attached, It is desirable that the decrease in performance be within an allowable range. Of course, if a hydrophilic agent having sufficient conductivity is used, it is possible to determine the ratio of the hydrophilic agent to be attached without considering the increase in resistance value.

As described above, when a substance having hydrophilicity is attached to the surface of the electrode base material as the hydrophilic treatment applied to the electrode base material, the electrode base material is immersed in a liquid containing the hydrophilic treatment agent. It can be easily achieved by dipping. In addition to the above method of making the electrode base material hydrophilic, a method of chemically treating the electrode base material to change the surface chemical structure of the electrode base material to improve hydrophilicity Can also be taken. Also in this case, if the battery performance is deteriorated by performing the above treatment, it is preferable that the deterioration of the battery performance is within an allowable range as compared with the effect obtained by the hydrophilic treatment.

Further, in this embodiment, PTFE was used for producing the water repellent carbon, but as the water repellent substance,
A sufficient amount of water repellency can be added to the cathode 23 with a usage amount such that the increase in the resistance value due to the provision of the water repellent layer on the surface of the gas diffusion electrode is within an allowable range, and the carbon powder can be uniformly mixed. Any substance that is possible and can withstand the manufacturing process conditions of the cathode 23 and the operating conditions of the fuel cell 20 may be used. Furthermore, in this example, as a dispersant, Trit was used.
Although onX-100 is used, other kinds of surfactants may be used as long as they can help the carbon powder and the water-repellent substance to be uniformly dispersed. However, it is desirable that it can be finally removed by firing or the like.

In the above-described embodiment, the same amount of water-repellent carbon is applied to both surfaces of the cathode 23, but in the second embodiment described below, the amount of water-repellent carbon on the electrolyte membrane 21 side is set to the oxidizing gas flow channel 25P side. The cathode 23a was formed with a larger amount of water repellent carbon. The fuel cell 20a and the fuel cell system 30a were constructed in the same manner as in the first embodiment except that the amount of water repellent carbon applied to each surface of the cathode 23a was changed. Second
Example In the following description, in each part constituting the fuel cell, the same parts as those in the first example except for the cathode are denoted by the same reference numerals as those in the first example.

In the second embodiment, when the amount of water-repellent carbon on the electrolyte membrane 21 side is made larger than that on the oxidizing gas flow channel 25P side, the amount of water-repellent carbon on the electrolyte membrane 21 side is simply increased. If so, the total amount of the water-repellent carbon applied to both surfaces of the cathode 23a will increase. Since PTFE that constitutes the water-repellent carbon does not have conductivity, in such a case, the electrode resistance increases and the battery performance rather deteriorates. Therefore, in the second embodiment, the total amount of water-repellent carbon is set to be the same as in the first embodiment, and only the application ratio is changed on both surfaces of the cathode 23a. The electrolyte membrane 21 side was applied at a rate of 6 mg / cm ^2, the oxidizing gas passage 25P side was applied at a rate of 2 mg / cm ^2.

The result of 1 A / cm ² constant current discharge generated by power generation using the fuel cell 20a configured as described above is shown in FIG. As compared with the case of the first embodiment in which equal amounts of water-repellent carbon were applied to both surfaces of the cathode 23, a high voltage could be stably obtained.

In the cathode 23a of the fuel cell 20a of the second embodiment, the amount of water repellent substance contained in the electrolyte membrane side water repellent part 62 is larger than the amount of water repellent substance contained in the gas channel side water repellent part 64. Since it is formed as described above, in addition to the effect obtained by hydrophilically treating the cathode 23 in the first embodiment, the following effect is obtained. That is, since the water repellency of the electrolyte membrane-side water-repellent portion 62 is improved in the cathode 23a, the action of the generated water being repelled and pushed back to the electrolyte membrane 21 is strengthened, and as an arrow for pushing water back to the electrolyte membrane side in FIG. The power expressed is becoming stronger. Therefore, the wet state of the electrolyte membrane 21 can be more favorably maintained, and it is possible to prevent an increase in battery resistance due to the drying of the electrolyte membrane 21 and obtain a high voltage. Further, in the cathode 23a, the water repellency of the electrolyte membrane side water repellent portion 62 is improved and the generated water is repelled, so that the gas diffusivity at this portion is further improved and the battery reaction is promoted.
It has become possible to output a higher voltage. Of course, if a water-repellent substance having conductivity is used instead of PTFE when producing water-repellent carbon, the cathode 2
It is also possible to increase the total amount of water-repellent carbon applied to 3a.

Further, since the cathode 23a in the fuel cell 20a of the second embodiment has a smaller amount of water-repellent carbon applied to the oxidizing gas passage 25P side than the cathode 23 of the first embodiment, the oxidizing gas passage 25P is formed. Oxidizing gas supplied from the battery is easily permeated, and the battery performance is also improved. By coating the water repellent carbon on the side of the oxidizing gas flow channel 25P, it is possible to prevent the water film of the generated water from being stretched and hindering the diffusion of the gas. The applied water-repellent carbon is
It also prevents the diffusion of gas from the oxidizing gas channel 25P.
On the side of the electrolyte membrane 21 where the generated water is generated, the diffusibility of gas is improved by providing water repellency as described above, but on the side of the oxidizing gas channel 25P to which the dry gas is supplied under pressure, water repellent carbon is generated. The application on the contrary hinders gas diffusion. The cathode 23a of the second embodiment can improve the diffusivity of the oxidizing gas by reducing the water-repellent carbon while maintaining the water repellency that repels excess generated water on the oxidizing gas flow path 25P side. .

As described above, in the second embodiment, the cathode 23
The water repellency on the electrolyte membrane 21 side was enhanced by changing the ratio of the water repellent carbon applied to both surfaces of a. By strengthening the water repellency on the electrolyte membrane 21 side of the cathode 23a, it is possible to prevent the electrolyte membrane 21 from drying and improve the gas diffusibility at the cathode 23a, and it is possible to increase the output voltage. In addition, when using a water repellent material that does not have sufficient conductivity, there is a problem of electrode resistance. Therefore, there is a limit to the method of increasing the amount of water repellent carbon to be applied to enhance water repellency. Here, in order to improve the water repellency of the electrode surface by a method other than increasing the amount of the water repellent carbon, a method of improving the water repellency of the water repellent carbon itself can be considered.

The water repellency of the water-repellent carbon is given by the water-repellent substance (PTFE in this embodiment) attached to the carbon powder, and the water repellency of the water-repellent carbon is increased by increasing the amount of PTFE attached to the carbon powder. Can be improved. However, in such a case, as in the case of increasing the total amount of water-repellent carbon, PT that does not have conductivity is used.
Since the amount of FE increases, the resistance value of the electrode increases and it is difficult to adopt. FIG. 9 shows the results of measuring the resistance value of the gas diffusion electrode when the gas diffusion electrode was formed by changing the amount of PTFE in the water-repellent carbon. As can be seen from FIG.
PTF, which has been the condition for producing water-repellent carbon in the past
If the PTFE amount is increased to exceed the E amount of 50%, the resistance value of the gas diffusion electrode is greatly increased.

As another method for improving the water repellency of the water-repellent carbon itself, it is considered to improve the water repellency of the carbon powder to which the water-repellent substance is attached. Conventionally, furnace black has been used as the carbon powder for producing the water-repellent carbon. If the resistance value is within the allowable range and carbon that is more water repellent than furnace black is used, the water repellency of the water repellent carbon itself can be improved more than before. Therefore, other carbon species, acetylene black and graphitized black, were compared with furnace black in terms of conductivity and water repellency.

First, water-repellent carbon was prepared by using furnace black, acetylene black, and graphitized black in accordance with the above-described examples, and each water-repellent carbon was applied to carbon cloth to prepare an electrode. .
When the resistance value of each of these electrodes was measured, as shown in FIG. 10, there was no great difference in the resistance value regardless of which carbon species was used to produce the water-repellent carbon. In this case, the amount of PTFE mixed when producing the water-repellent carbon was equal to the amount of carbon regardless of which carbon was used.

Next, the water repellency of these carbon species was compared. It is considered that each carbon contains some functional groups in its structure, but it is considered that the more hydrophilic functional groups are, the lower the water repellency of the carbon is. Therefore, first, the amount of functional groups contained in each carbon was measured. FIG. 11 shows the results of measuring the functional groups of each carbon by the back titration method. The back titration method is a method in which a known amount of the first standard solution is added so that it becomes excessive with respect to the sample, and then this excess amount is titrated with the second standard solution to finally quantify the sample. is there. In particular, it is effective when the reaction rate between the sample and the standard solution is slow, or when the reaction reaches equilibrium and is difficult to proceed. Here, a sodium hydroxide solution was used as the first standard solution, and a hydrochloric acid solution was used as the second standard solution. Thus, FIG. 11 shows the results of measuring only acidic functional groups, but the main hydrophilic group is the carboxyl group,
Since the phenolic group is acidic, it is a measure of hydrophilicity. From the results of FIG. 11, it is expected that acetylene black and graphitized black have stronger water repellency than furnace black.

Further, in FIG. 12, the water repellency of each carbon was compared by measuring the contact angle when ethanol of various concentrations was dropped. Here, for each carbon, water-repellent carbon was prepared according to the above-mentioned example, and a gas diffusion electrode having the surface coated with each water-repellent carbon was prepared, and ethanol of various concentrations was dropped on each gas diffusion electrode. After that, the state was photographed and the contact angle was measured. The contact angle is an angle formed by the surface of the dropped water droplet and the surface on which the droplet is dropped, and the stronger the water repellency is, the stronger the water droplet is repelled and the larger the contact angle. Here, ethanol was used in place of water when investigating the water repellency, but since ethanol has a property of being more easily repelled than water, the contact angle becomes large, and the measurement is easy and the difference is easy to understand. Therefore, it was decided to perform evaluation using various concentrations of ethanol in this way. From the measurement of the contact angle shown in FIG. 12, it was also obtained that the acetylene black and the graphitized black had stronger water repellency than the furnace black.

From the above results, water repellent carbon was produced using acetylene black and graphitized black, which are considered to have stronger water repellency than the conventionally used furnace black, and a fuel cell was assembled. A constant current discharge of 1 A / cm ² was performed on a fuel cell 20b having a cathode 23b coated with water-repellent carbon made of acetylene black and a fuel cell 20c having a cathode 23c coated with water-repellent carbon made of graphitized black. The results obtained are shown in FIG. 8 as a graph of symbols f and g as a third embodiment. In any case, a higher voltage could be stably obtained as compared with the fuel cell 20 using the water repellent carbon made of furnace black. Of course, in the cathodes 23b and 23c, the electrode base material is subjected to the hydrophilic treatment described above.

Fuel cells 20b and 2 of the third embodiment
At 0c, the water repellency of the water-repellent carbon applied to the electrode surface is further improved, so that the generated water generated by the battery reaction is more likely to be pushed back, and the pushed-back generated water is deposited on the dry portion of the electrolyte membrane 21. Since it is transmitted promptly, the wet state of the electrolyte membrane 21 is more favorably maintained. Therefore, it is possible to prevent the voltage from dropping due to the electrolyte membrane 21 drying and the resistance value increasing during the power generation of the fuel cell. Further, since the water repellency of the water repellent carbon is further improved, the cathode 23
The gas diffusivity of b and the cathode 23c was improved, the cell reaction was promoted, and a higher voltage could be obtained.

As described above, the cathodes 23b and 23
When forming c, water-repellent carbon is applied onto the electrode substrate that has been subjected to a hydrophilic treatment, and at this time, in particular, by enhancing the water repellency on the electrolyte membrane 21 side, the oxidizing gas according to the set conditions shown in FIG. Even when power generation is performed under a set condition in which the air is not humidified and the excess air ratio is low, it is possible to maintain the wet state of the electrolyte membrane 21 and realize high gas diffusivity.

In the first to third embodiments, the cathode 23 has a structure in which water repellent carbon is applied to both surfaces thereof. The water-repellent carbon applied to the surface on the oxidizing gas flow path 24P side repels the generated water when it condenses on the oxidizing gas flow path 24P side to promote drainage. However, in the cathode 23, if the performance of the fuel cell 20 is within the allowable range even if there is no water-repellent carbon applied on the oxidizing gas flow path 24P side, the water-repellent carbon is applied on the oxidizing gas flow path 24P side. It may be configured not to. However, cathode 2
When the carbon cloth constituting No. 3 directly contacts the separator 25 without being coated with carbon powder, the contact area of the conventional carbon cloth is insufficient, which may result in poor current collection. Therefore, in the case where the water repellent carbon is not applied to the oxidizing gas flow path 24P side, it is sufficient to secure the current collecting property by using a carbon cloth having a sufficiently fine weave. Further, carbon powder that has not been subjected to a water repellent treatment may be applied to the oxidizing gas flow path 24P side to secure the current collecting property. At this time, if carbon powder having strong water repellency is used, it is possible to impart a predetermined water repellency together with the current collecting property.

In the above embodiment, PTFE having no conductivity is used.
Water-repellent carbon was produced by adhering to the carbon powder, and the surface of the cathode 23 was made water-repellent by applying this water-repellent carbon. The water repellency of the surface of 23 may be improved. In such a case, the conductive water-repellent substance is directly made into a paste to form the cathode 2
3 can be applied to the surface, and the step of attaching the water-repellent substance to the conductive carrier can be omitted.

In the first to third embodiments, as the anode 22, as in the case of the conventionally used gas diffusion electrode, an untreated carbon cloth coated with water-repellent carbon was used. In the fourth example, the fuel cell 20d was assembled by using the cathode 23c used in the third example and the hydrophilically treated anode 22d. This anode 22
d was manufactured similarly to the cathode 22 of the first embodiment. That is, the carbon cloth is hydrophilized to have SiO ₂ adhered at a rate of 0.5%, and the water-repellent carbon with PTFE adhered to both surfaces of the hydrophilically treated carbon cloth is 4 mg / cm ² on each side. Was applied.

A graph h is shown in FIG. 8 as a result of carrying out power generation using such a fuel cell 20d and performing constant current discharge of 1 A / cm ² . Fuel cell 20c of the third embodiment
It was possible to stably generate power at a voltage higher than that in the case of using. The voltage level obtained here is almost the same as the voltage level obtained when the fuel cell using the conventional gas diffusion electrode not subjected to the hydrophilic treatment is operated according to the conventional condition shown in FIG. 13 (see FIG. 15).

According to the fuel cell 20d of the fourth embodiment, since the carbon cloth, which is the electrode base material of the anode 22d, is subjected to the hydrophilic treatment using SiO ₂ , the anode 22d
d can efficiently absorb and pass the steam supplied together with the fuel gas, and the steam thus absorbed can be supplied to the electrolyte membrane 21 which tends to lose water as the cell reaction proceeds. Therefore, the fuel cell 20d
Then, it becomes possible to prevent the drying of the electrolyte membrane 21 more effectively.

Further, in the fuel cell 20d of this embodiment, even if water vapor condenses in the fuel gas passage 24P,
Water droplets are repelled by the water-repellent carbon applied to the surface of the anode 22d on the fuel gas flow path 24P side, and drainage is promoted. Therefore, even if water vapor condenses on the side of the fuel gas flow path 24P, a film of water will not form on the surface of the anode 22d and the diffusion of gas will not be hindered.

Thus, the fuel cell 20d of the fourth embodiment is
In the above, even if the base portion of the anode 22d is subjected to the hydrophilic treatment, even if the fuel gas having a humidity of 60% is supplied as it is based on the setting conditions shown in FIG.
It has become possible to sufficiently maintain the wet state of the electrolyte membrane 21.

In the fuel cell 20d of the fourth embodiment, in the positive electrode, as in the first to third embodiments, the hydrophilicity of the electrode base is strengthened and the water repellency on the electrolyte membrane 21 side is strengthened, and the negative electrode is used. In, the hydrophilicity of the electrode base is enhanced. As a result, even when power generation is performed based on the set conditions of FIG. 13, it is possible to stably obtain a voltage level that is substantially the same as that when power generation is performed according to the conventional conditions by the conventionally used electrodes that have not been subjected to the hydrophilic treatment. It was As described above, the fuel cell 20d of the fourth embodiment has the excellent cell performance of stably outputting a high voltage,
Since it is possible to generate power based on the setting condition that the amount of energy consumed for power generation is 10% of the amount of power generation, there is an excellent effect that the energy efficiency of the entire system can be greatly improved.

The set conditions in FIG. 13 are set so that the energy consumed for power generation in the fuel cell system 30 is 10% of the amount of power generation, and the humidification of the supplied gas is actively performed. Although the excess air ratio is set to 2 because it does not exist, the power generation condition of the fuel cell does not have to be as strict as the set condition as long as the energy consumption is within the allowable range. The fuel gas or the oxidizing gas may be humidified using energy in a predetermined range, or the excess air ratio may be set to a predetermined value of 2 or more. Also in this case, the effects of the first to fourth embodiments of the present invention can be similarly obtained, and the output voltage can be increased and stabilized.
For example, when the energy consumption for power generation allows even 20% of the power generation amount, the excess air ratio can be set to 3, so that the gas diffusivity and the generated water drainage are increased by increasing the supply amount of the oxidizing gas. It is possible to further improve battery performance and improve battery performance. Further, even when the excess air ratio is set to 3, it is possible to suppress a decrease in energy efficiency of the entire system by using a compressor having higher energy efficiency than the pump 36.

In the fourth embodiment, by using the above-mentioned anode 22d together with the cathode 23c used in the third embodiment, the effect as shown in FIG. 8 can be obtained. Fourth obtained by using the anode 22d
The effect in the embodiment is an effect independent of the cathode side. Therefore, the same effect can be seen when the above-mentioned anode 22d is used together with the cathode 23, the cathode 23a or the cathode 23b used in the above-mentioned first or second embodiment, and in that case, as shown in FIG. It becomes possible to obtain a higher voltage than the results of the first and second embodiments.

In the fourth embodiment, the water-repellent carbon is applied to both surfaces of the anode 22d, but such water-repellent carbon may not be applied to at least one surface. In particular, on the surface that is in contact with the electrolyte membrane 21, water is not generated unlike the cathode side, so the water repellency does not help maintain the wet state of the electrolyte membrane 21. When the water repellent carbon is not applied, the hydrophilized electrode base material comes into direct contact with the electrolyte membrane 21,
The water absorbed by the electrode base material can be directly given to the electrolyte membrane 21, which may be rather advantageous in maintaining the wettability of the electrolyte membrane 21. Therefore, on the surface in contact with the electrolyte membrane 21, if the deterioration of the battery performance when the improvement of the gas diffusivity due to the application of the water-repellent carbon is eliminated is within the allowable range, do not apply the water-repellent carbon. Can be

On the surface on the fuel gas channel 24P side, when the water-repellent carbon is not applied, the water droplets condensed in the channel are directly absorbed by the hydrophilized electrode substrate and supplied to the electrolyte membrane 21. This makes it possible to obtain an effect different from the case where the water repellent carbon repels water droplets to promote drainage. Therefore, it is possible not to apply the water-repellent carbon to the surface on the fuel gas flow path 24P side.
As described above, providing the water-repellent region on each surface of the anode 22d may have contradictory effects in moistening the electrolyte membrane 21 and maintaining gas diffusivity, and thus a water-repellent layer is provided on each surface. Whether or not to decide whether or not to meet the above conditions may be determined according to the operating conditions of the battery.

However, when the water-repellent carbon is not applied, if the gas diffusion electrode is formed of carbon cloth as in the above-mentioned embodiment, the contact area becomes insufficient and the current collecting property becomes insufficient. It is necessary to secure the current collecting property by using a fine carbon cloth. Alternatively, it is possible to apply carbon powder that is not subjected to water repellent treatment to ensure current collection. Further, when the fuel cell is operated under the condition that it is advantageous that the surface of the negative electrode has a strong hydrophilicity, the carbon powder hydrophilized by SiO ₂ or the like is applied to enhance the hydrophilicity of the electrode surface and to collect the particles. You may secure electric property.

Although the solid polymer electrolyte fuel cell has been described in this embodiment, the present invention is applied to the electrodes of other types of fuel cells such as phosphoric acid fuel cells in which wetting of the electrodes is a problem. Even if applied, the same effect can be obtained.

The embodiment of the present invention has been described above.
It is needless to say that the present invention is not limited to these embodiments and can be implemented in various modes without departing from the scope of the present invention.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing how the produced water and oxidizing gas move in a cathode 23 of a fuel cell 20.

FIG. 2 is a block diagram illustrating the configuration of a fuel cell system 30.

FIG. 3 is a schematic sectional view illustrating the configuration of a single cell 28.

FIG. 4 is an explanatory diagram showing a configuration of an evaporation rate measuring device 50 for evaluating hydrophilicity included in a gas diffusion electrode.

FIG. 5 is an explanatory diagram showing a graph of the relationship between the amount of evaporated water measured by the evaporation rate measuring device 50 and the time required for evaporation.

FIG. 6 is an explanatory diagram showing the relationship between the amount of adhesion of a hydrophilic substance and the drainage property of the gas diffusion electrode.

FIG. 7 is an explanatory diagram showing the relationship between the adhesion amount of a hydrophilic substance and the resistance value of a gas diffusion electrode.

FIG. 8 is 1 A / cm ² using the gas diffusion electrode of each example.
It is explanatory drawing which shows the result of performing constant current discharge.

FIG. 9: PT attached when manufacturing a gas diffusion electrode
It is explanatory drawing which shows the relationship between FE amount and electrode resistance.

FIG. 10 is a graph showing carbon species used when producing water-repellent carbon,
It is explanatory drawing which shows the relationship with the resistance value which the electrode which each water-repellent carbon apply | coated has.

FIG. 11 is an explanatory diagram showing the result of quantifying the amount of functional groups contained in each carbon species.

FIG. 12 is an explanatory diagram showing the results of evaluating the water repellency of each carbon species.

FIG. 13 is an explanatory diagram showing conditions for operating the fuel cell.

FIG. 14 is an explanatory diagram showing energy consumed by a pump for pressurizing and supplying air.

FIG. 15 is an explanatory diagram showing a result of constant current discharge of 1 A / cm ² for a conventional fuel cell.

[Explanation of symbols]

 20, 20a, 20b, 20c, 20d ... Fuel cell 21 ... Electrolyte membrane 22 ... Anode 22, 22d ... Cathode 23, 23a, 23b, 23c ... Cathode 24, 25 ... Separator 24P ... Fuel gas channel 25P ... Oxidizing gas channel 26 ... Current collector plate 28 ... Single cell 30, 30a ... Fuel cell system 31 ... Methanol tank 32 ... Water tank 34 ... Reformer 36 ... Pump 37 ... Pressure regulating valve 38 ... Fuel supply passage 39 ... Air supply passage 40 ... Branched air Channel 41 ... Exhaust path 50 ... Evaporation rate measuring device 51 ... Water tank 52 ... Nitrogen cylinder 54 ... Water level gauge 55 ... Heater 56 ... Nitrogen flow path 57 ... Flow rate adjusting section 58 ... Gas diffusion electrode 60 ... Hydrophilic section 62 ... Electrolyte membrane side Water-repellent part 64 ... Water-repellent part on gas flow path side

Claims (8)

[Claims] 1. A fuel cell comprising an electrolyte layer and a positive electrode and a negative electrode sandwiching the electrolyte layer, wherein the positive electrode comprises at least a surface of an electrode base material subjected to a hydrophilic treatment on the electrolyte layer side, A fuel cell comprising a water repellent layer having a water repellent substance. 2. The fuel cell according to claim 1, wherein the positive electrode has the water-repellent layer formed on both sides thereof using a water-repellent substance having no conductivity, and the positive electrode is provided on a side in contact with the electrolyte layer. The formed water-repellent layer is a fuel cell containing more water-repellent substance than the water-repellent layer formed on the other surface. 3. The water-repellent layer is formed by mixing the water-repellent substance and carbon powder having a hydrophilic functional group content of a predetermined amount or less, and then coating the surface of the electrode substrate. The fuel cell according to claim 1 or 2. 4. The fuel cell according to claim 1, wherein the negative electrode is made of an electrode base material subjected to a hydrophilic treatment. 5. A fuel cell electrode having predetermined conductivity and gas permeability, wherein a water-repellent layer including a water-repellent substance is formed on at least one surface of a hydrophilically treated electrode base material. Battery electrode. 6. The electrode for a fuel cell according to claim 5, wherein the water repellent layer is formed on both surfaces of the electrode base material by using a substance having no conductivity, and both surfaces of the electrode base material are formed. The water repellent layers formed on the fuel cell electrode contain different amounts of the water repellent substances. 7. The water-repellent layer is formed by mixing the water-repellent substance and carbon powder having a hydrophilic functional group content of a predetermined amount or less, and then coating the surface of the electrode substrate. The electrode for a fuel cell according to claim 5 or 6. 8. A fuel cell comprising an electrolyte layer and a positive electrode and a negative electrode sandwiching the electrolyte layer, and gas supply means for supplying fuel gas and air to the fuel cell at a predetermined pressure and a predetermined excess air ratio. In the fuel cell system including: a positive electrode of the fuel cell, a water-repellent layer having a water-repellent substance is formed on at least the surface of the electrode base material subjected to hydrophilic treatment on the electrolyte layer side, A fuel cell system, wherein the excess air ratio of the air supplied by the means is 3 or less.