JP2006324140A - Cathode electrode for fuel cell and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cathode electrode for a fuel cell capable of lowering activation overvoltage and sufficiently durable to the long operation of the fuel cell and to provide fuel cell using it. <P>SOLUTION: The cathode electrode for the fuel cell contains a catalyst and oxygen transmitting resin represented by general formula (1). In the general formula (1), R<SP>1</SP>-R<SP>4</SP>independently represent a group selected from an alkyl group, a fluorine substituted alkyl group, and an alkylated silyl group, and n represents an integer of 100-10,000. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a cathode electrode for a fuel cell and a fuel cell, and more particularly to a cathode electrode capable of reducing activation overvoltage at the cathode and a fuel cell using the cathode electrode.

  There are various types of fuel cells. Recently, a polymer electrolyte type fuel cell having an operating temperature of about 80 ° C. to 100 ° C., or a phosphoric acid type having an operating temperature of about 150 ° C. to 200 ° C. Fuel cells are in practical use. The basic structure of these solid polymer type or phosphoric acid type fuel cells is roughly composed of an anode electrode and a cathode electrode, and an electrolyte inserted between these electrodes. The anode electrode and the cathode electrode are porous bodies formed by mixing catalyst powder and a binder resin and solidifying and forming into a sheet shape. An electrolyte is in contact with one side of the cathode electrode, and an oxygen supply channel is provided on the other side. At the time of power generation, oxygen is supplied from the oxygen supply channel to the cathode electrode and hydrogen ions are supplied from the electrolyte side, and electrons from an external circuit are supplied to the electrode itself. On the catalyst surface, oxygen is reduced by hydrogen ions and electrons to form water.

  By the way, since the activation overvoltage is relatively high in the oxygen reduction reaction at the cathode electrode, the reaction rate of the reduction reaction itself is slower than the hydrogen oxidation reaction at the anode electrode. For this reason, there is a problem that the output voltage of the fuel cell is also lowered due to the effect of the activation overvoltage. In order to reduce the activation overvoltage, it is necessary to improve the oxygen concentration on the catalyst surface.

  In order to improve the oxygen concentration on the catalyst surface, there is a method of increasing the porosity of the cathode electrode itself and supplying more oxygen to the catalyst surface. However, in this method, moisture is easily retained by making the electrode porous, and the catalyst surface may be covered with water, and the oxygen reduction reaction may not proceed.

Thus, a method is disclosed in which polydimethylsiloxane having excellent oxygen permeability is used as the binder resin for solidifying and molding the catalyst powder, and the activation overvoltage is reduced by increasing the amount of oxygen supplied to the catalyst surface (Patent Document 1). ).
JP 2002-289202 A

  However, although polydimethylsiloxane is excellent in oxygen permeability, it has a problem of low thermal stability and oxidation resistance. Accordingly, in the fuel cell in which polydimethylsiloxane is added to the cathode electrode, there is a problem in that the oxygen permeability of the polydimethylsiloxane gradually decreases and the output voltage gradually decreases as the operation time becomes longer. .

As a result of intensive studies by the present inventors in view of the above circumstances, an oxygen permeable material having excellent oxygen permeability and excellent heat resistance and oxidation resistance was discovered, thereby completing the present invention.
Accordingly, an object of the present invention is to provide a cathode electrode for a fuel cell that can reduce the activation overvoltage and sufficiently withstand long-term operation of the fuel cell, and a fuel cell using the same.

ただし、上記一般式（１）において、Ｒ^１〜Ｒ^４は独立して、アルキル基、フッ素置換アルキル基、アルキル化シリル基から選択されたものを表し、ｎは１００以上１００００以下の整数を表す。
また本発明の燃料電池用のカソード電極においては、上記酸素透過性樹脂の酸素透過係数Ｐ_Ｏ２が１×１０^−１１［ｃｍ^３（標準状態）・ｃｍ／ｃｍ^２・ｓ・Ｐａ］以上であることが好ましい。
また本発明の燃料電池用のカソード電極においては、前記酸素透過性樹脂がポリ（１−トリメチルシリルプロピン）であることが好ましい。
次に本発明の燃料電池は、先のいずれかに記載の燃料電池用のカソード電極を備えたことを特徴とする。 In order to achieve the above object, the present invention employs the following configuration.
The cathode electrode for a fuel cell according to the present invention is characterized by containing a catalyst and an oxygen-permeable resin represented by the following general formula (1).

However, in the above general formula ^(1), R 1 ~R ⁴ are independently an alkyl group, fluorine-substituted alkyl group, those selected from alkylated silyl group, n is an integer of 100 to 10,000 .
In the cathode electrode for the fuel cell of the present invention, the oxygen permeable coefficient P _O2 of the oxygen permeable resin is 1 × 10 ⁻¹¹ [cm ³ (standard state) · cm / cm ² · s · Pa] or more. It is preferable.
In the cathode electrode for a fuel cell of the present invention, the oxygen permeable resin is preferably poly (1-trimethylsilylpropyne).
Next, a fuel cell according to the present invention is characterized by including the cathode electrode for a fuel cell as described above.

  The oxygen permeable resin represented by the general formula (1) is excellent in oxygen permeability, can withstand a high temperature of about 200 ° C., and has excellent oxidation resistance. By using a material having such properties for the cathode electrode, it becomes possible to increase the oxygen concentration on the catalyst surface in the cathode electrode and reduce the activation overvoltage. Moreover, even when used as an electrode of a fuel cell that is continuously operated at a high temperature of 80 ° C. to 200 ° C. for a long period of time, it is possible to maintain a high output voltage without reducing the oxygen permeation capability.

Among the oxygen permeable resins represented by the general formula (1), those having an oxygen permeability coefficient PO ₂ of 1 × 10 ⁻¹¹ [cm ³ (standard state) · cm / cm ² · s · Pa] or more. By using it, the oxygen concentration on the catalyst surface can be further increased and the activation overvoltage can be reduced.

  According to the cathode electrode for a fuel cell of the present invention, it is possible to provide a cathode electrode for a fuel cell that can reduce the activation overvoltage and can sufficiently withstand long-term operation of the fuel cell, and a fuel cell using the same.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the fuel cell of this embodiment includes a cathode electrode 2 and an anode electrode 3 according to the present invention, an electrolyte 4 sandwiched between the cathode electrode 2 and the anode electrode 3, and an outer side of the cathode electrode 2. The oxidant distribution plate 5 having the oxidant flow path 5a disposed on the anode electrode 3 and the fuel flow distribution plate 6 having the fuel flow path 6a disposed outside the anode electrode 3 are formed at a temperature of 80 ° C. to 200 ° C. It works.

  The oxidant distribution plate 5 and the fuel distribution plate 6 are made of a conductive metal or the like, and function as a current collector by being joined to the cathode electrode 2 and the anode electrode 3, respectively. Oxygen and fuel are supplied to the electrode 3. That is, hydrogen, which is fuel, is supplied to the anode electrode 3 through the fuel flow path 6 a of the fuel flow distribution plate 6, and the cathode electrode 2 is oxidized through the oxidant flow path 5 a of the oxidant flow distribution plate 5. Oxygen as an agent is supplied. Note that hydrogen supplied as fuel may be hydrogen generated by reforming hydrocarbons or alcohols, and oxygen supplied as oxidant may be supplied in a state of being contained in air.

  In this fuel cell, hydrogen is oxidized on the anode electrode 3 side to generate protons (hydrogen ions), which are conducted through the electrolyte 4 and reach the cathode electrode 2. Further, as hydrogen at the anode electrode 3 is oxidized, electrons flow from the anode electrode 3 to the external circuit, and the electrons flow into the cathode electrode. In the cathode electrode 2, hydrogen ions, oxygen and electrons react electrochemically, oxygen is reduced to produce water, and electric energy is generated.

The electrolyte 4 has proton conductivity and is preferably a solid polymer electrolyte that operates at 80 ° C. to 100 ° C. or a phosphoric acid electrolyte that operates at 150 ° C. to 200 ° C. In the present invention, an electrolyte that operates between 100 ° C. and 150 ° C. may be used.
As a material of the solid polymer electrolyte, for example, a perfluorocarbon sulfonic acid type ion exchange membrane or a hydrocarbon type polymer electrolyte membrane is preferable.
Moreover, as a material of the phosphoric acid electrolyte, for example, a material obtained by impregnating a basic polymer with one or more acids of phosphoric acid, polyphosphoric acid, phosphonic acid, and sulfuric acid is preferable. Among the acids, phosphoric acid is preferably impregnated in an 85% orthophosphoric acid aqueous solution, and is preferably set to a doping amount of about 200 to 1000 mol% per one functional group of the basic polymer. When the basic polymer holds phosphoric acid or the like, hydrogen ions such as phosphoric acid are partially dissociated, and ion conductivity is imparted to the electrolyte membrane 4 by the hydrogen ions. Examples of basic polymers that retain phosphoric acid include polybenzimidazole, poly (pyridine), poly (pyrimidine), polyimidazole, polybenzothiazole, polybenzoxazole, polyoxadiazole, polyxylone, polyquinoxaline, and polyriadiazole. , Poly (tetrazabilene), polyoxazole, polyvinyl pyridine, polyvinyl imidazole, and derivatives thereof, or one or more thereof. In particular, it is preferable to use polybenzimidazole represented by the following [Chemical Formula 2] as the basic polymer. The average molecular weight of the basic polymer is preferably 1000 to 100,000. Further, a phosphoric acid electrolyte obtained by impregnating a porous silicon carbide body with phosphoric acid may be used.

Next, the cathode electrode 2 according to the present invention is roughly composed of a porous catalyst layer 2a and a porous carbon sheet (carbon porous body) 2b holding the catalyst layer 2a. The catalyst layer 2a is composed of an electrode catalyst (catalyst) in which any one of platinum, an alloy of platinum and other noble metal (for example, ruthenium) or an alloy of platinum and a base metal (for example, cobalt) is supported on activated carbon, and the following general The oxygen permeable resin represented by the formula (2) is contained at least. In the catalyst layer 2a, it is desirable that the oxygen permeable resin is not in the form of a film but in a form in which the oxygen permeable resin is dispersed in the catalyst. In the following general formula (2), R ^{1 to} R ⁴ independently represent an alkyl group, a fluorine-substituted alkyl group, or an alkylated silyl group, and n represents an integer of 100 or more and 10,000 or less. .

In the general formula (2), R ^{1 to} R ⁴ are independently selected from an alkyl group having 1 to 5 carbon atoms, a fluorine-substituted alkyl group having 1 to 5 carbon atoms, and a trimethylated silyl group. More preferably, R ^{1 to} R ⁴ are independently independently an alkyl group having 1 to 3 carbon atoms, and R ^{1 to} R ⁴ are all methyl groups. Pin) is particularly preferable.

The oxygen permeable resin represented by the general formula (2) is a resin in which hydrogen of polyacetylene is substituted with the R ¹ group and the R ^{2 to} R ⁴ substituted silyl group. Since this oxygen-permeable resin has a main chain of a polyacetylene structure, the molecular chain has high rigidity, so that the distance between the main chains is wider than that of a general glassy polymer. Further, in this oxygen permeable resin, R ^{2 to} R ⁴ substituted silyl groups having high mobility exist between the extended main chains. The oxygen permeable resin having such a molecular structure has an oxygen permeability of 10 times or more compared to conventional polydimethylsiloxane and the like. In addition, since the polyacetylene chain constituting the main chain is excellent in heat resistance and oxidation resistance, the oxygen-permeable resin according to the present invention is suitable as an electrode constituent material of a fuel cell. In particular, the oxygen-permeable resin according to the present invention is not decomposed even in an oxidizing atmosphere of 200 ° C. or higher, and can be suitably used as an electrode constituent material of a fuel cell.
The oxygen permeability coefficient P _{O2 that} is preferable as the oxygen permeable resin according to the present invention is 5 × 10 ⁻¹¹ [cm ³ (standard state) · cm / cm ² · s · Pa] or more, and more preferably 1 × 10 9. ^-10 [cm ³ (standard state) · cm / cm ² · s · Pa] or more. The oxygen permeability coefficient P _O2 of poly (1-trimethylsilylpropyne) most preferable as the oxygen permeable resin is 1 × 10 ⁻¹⁰ to 1 × 10 ⁻⁹ [cm ³ (standard state) · cm / cm ² · s · Pa. ] By using a resin having an oxygen permeability coefficient P _O2 of 1 × 10 ⁻¹¹ [cm ³ (standard state) · cm / cm ² · s · Pa] or more, activation overvoltage in the cathode electrode 2 can be reduced. .

  In addition, the oxygen-permeable resin represented by the general formula (2) has excellent heat resistance when the weight reduction start temperature is 200 ° C. or higher when the weight reduction start temperature is measured by thermogravimetric analysis. In particular, poly (1-trimethylsilylpropyne), the most preferred oxygen permeable resin, has a weight reduction starting temperature of 300 ° C. or higher, and has a heat resistance suitable as an electrode constituent material for a fuel cell operating at about 80 ° C. to 200 ° C. Have.

  Further, the blending ratio of the oxygen permeable resin to the catalyst is preferably in the range of 0.1% to 10% by mass%, and more preferably in the range of 2% to 8%. If the blending ratio is 0.1% or more, a sufficient concentration of oxygen can be supplied to the catalyst surface. If the blending ratio is 10% or less, the resistivity of the cathode electrode 2 itself can be kept low, and the internal resistance of the anode electrode can be reduced.

In addition to the catalyst and the oxygen permeable resin, the catalyst layer 2a of the cathode electrode 2 may be added with either a hydrophobic polymer, a basic polymer capable of holding phosphoric acid, or a proton conductive resin. . Moreover, you may add hydrophobic resin and a basic polymer simultaneously. Moreover, you may add hydrophobic resin and proton conductive resin simultaneously.
As the hydrophobic resin, for example, a resin having excellent hydrophobicity and heat resistance such as polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene / hexafluoroethylene copolymer, perfluoroethylene, and the like can be used. By adding the hydrophobic resin, it is possible to prevent the catalyst layer 2a from being wetted excessively by the water generated during the power generation reaction, and to prevent the diffusion of oxygen in the cathode electrode 2 from being inhibited. That is, a large number of gas phase (oxygen) -liquid phase (water) -solid phase (catalyst) three-phase interfaces are formed on the surface of the catalyst inside the cathode electrode 2, and the characteristics of the cathode electrode 2 can be improved.
Moreover, as a basic polymer, the basic polymer used for said electrolyte 4 can be utilized. The average molecular weight of the basic polymer is preferably 1000 to 100,000. This is because if the average molecular weight is 1000 or less, the adhesion to the catalyst is poor, and if the average molecular weight is 100,000 or more, it is difficult to dissolve in the solvent and mixing with the catalyst becomes difficult. By adding the basic polymer, phosphoric acid or the like that has oozed out of the electrolyte 4 can be held on the cathode electrode 2. Thereby, hydrogen ions can be efficiently transported to the catalyst surface of the cathode electrode 2, and the reaction rate of the oxygen reduction reaction can be increased.
Further, as the proton conductive resin, a fluorine ion exchange resin such as a perfluorocarbon sulfonic acid type ion exchange resin can be used. In particular, the fluorine-based ion exchange resin has oxygen selective solubility, and oxygen dissolved in the resin can be efficiently transported to the electrode surface. Thereby, hydrogen ions can be efficiently transported to the catalyst surface of the cathode electrode, the reaction rate of the oxygen reduction reaction can be increased, and the activation overvoltage can be further reduced.

The blending ratio of the hydrophobic resin in the catalyst layer 2a is preferably in the range of 1% to 20% by mass%, and more preferably in the range of 2% to 10%. By making the blending ratio of the hydrophobic resin 1% or more, the hydrophobicity of the catalyst layer 2a itself can be increased. Moreover, the internal resistance of the cathode electrode 2 can be reduced by setting the blending ratio of the hydrophobic resin to 20% or less.
Further, the blending ratio of the basic polymer in the catalyst layer 2a is preferably in the range of 0% to 10% by mass%, and more preferably in the range of 2% to 5%. By setting the blending ratio of the basic polymer to 2% or more, the hydrogen ion conductivity in the catalyst layer 2a can be increased and the oxygen reduction reaction can be efficiently advanced. Moreover, the internal resistance of the cathode electrode 2 can be reduced by setting the blending ratio of the basic polymer to 10% or less.
Furthermore, the blending ratio of the proton conductive resin in the catalyst layer 2a is preferably in the range of 0% to 10% by mass%, and more preferably in the range of 2% to 5%. By setting the blending ratio of the proton conductive resin to 2% or more, the hydrogen ion conductivity in the catalyst layer 2a can be increased, and the oxygen reduction reaction can be advanced efficiently. Moreover, the internal resistance of the cathode electrode 2 can be reduced by setting the blending ratio of the proton conductive resin to 10% or less.

In order to manufacture the catalyst layer 2a, for example, the catalyst and the oxygen permeable resin are mixed with a solvent in which the oxygen permeable resin is soluble to form a slurry, and this slurry is applied to the porous carbon sheet 2b. It can be produced by removing the solvent. A hydrophobic resin, a basic polymer, or a proton conductive resin may be added to the slurry. As a solvent in which the oxygen permeable resin is soluble, for example, toluene can be used.
If the hydrophobic resin, basic polymer, or proton conductive resin is insoluble in a solvent such as toluene, a catalyst layer is formed with the hydrophobic resin and the catalyst, and then an oxygen permeable resin is added. May be. Specifically, the catalyst and the hydrophobic resin are mixed with a solvent in which the hydrophobic resin is soluble to form a slurry, and the solvent is removed from the slurry to obtain a mixture. Next, a toluene solution in which the oxygen permeable resin is dissolved is prepared, and the mixture is added to the toluene solution and kneaded to form a slurry. The slurry is applied to the porous carbon sheet 2b, and toluene is further added. A catalyst layer is formed by removing. Alternatively, the toluene may be removed after applying the toluene solution to the mixture. In this way, a catalyst layer to which a hydrophobic resin or the like and an oxygen permeable resin are added is obtained.

  Next, the anode electrode 3 is roughly composed of a porous catalyst layer 3a and a porous carbon sheet (carbon porous body) 3b for holding the catalyst layer 3a. In the catalyst layer 3a, an electrode catalyst (catalyst) in which any one of platinum, an alloy of platinum and other noble metal (for example, ruthenium) or an alloy of platinum and a base metal (for example, cobalt) is supported on activated carbon, and this electrode And a hydrophobic binder for solidifying and molding the catalyst. As the hydrophobic binder, for example, a resin having excellent hydrophobicity and heat resistance such as polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene / hexafluoroethylene copolymer, perfluoroethylene, or the like can be used. By adding the hydrophobic binder, it is possible to prevent the catalyst layer 3a from being excessively wetted by the water generated by the power generation reaction, and to prevent the diffusion of fuel gas inside the anode electrode 3 from being inhibited. it can. That is, a large number of gas phase (hydrogen) -liquid phase (water) -solid phase (catalyst) three-phase interfaces are formed on the surface of the electrode catalyst inside the anode electrode 3, thereby improving the electrode characteristics. The catalyst layer 3a may contain a basic polymer in addition to the catalyst and the hydrophobic binder. By adding a basic polymer, it is possible to retain phosphoric acid and the like that have oozed out of the electrolyte 4. Thereby, hydrogen ions generated on the catalyst surface can be efficiently transported to the outside of the anode electrode. The basic polymer used for the electrolyte 4 can be used as the basic polymer added to the anode electrode 3. The average molecular weight of the basic polymer is preferably 1000 to 100,000. This is because if the average molecular weight is 1000 or less, the adhesion to the catalyst is poor, and if the average molecular weight is 100,000 or more, it is difficult to dissolve in the solvent and mixing with the catalyst becomes difficult.

  The oxygen permeable resin contained in the cathode electrode 2 according to the present invention is excellent in oxygen permeability, can withstand a high temperature of about 200 ° C., and is excellent in oxidation resistance. Part of the oxygen supplied from the oxidant flow path 5a to the cathode electrode 2 is absorbed by the porous catalyst layer 2a and reaches the catalyst surface, while the other part of the oxygen passes through the oxygen-permeable resin. Reach the catalyst surface. As described above, according to the cathode electrode 2 of the present embodiment, by containing the oxygen permeable resin, the oxygen concentration on the catalyst surface can be increased, and the activation overvoltage can be reduced. In addition, since it has excellent heat resistance and oxidation resistance, even when used as an electrode of a fuel cell that is continuously operated at a high temperature of 80 ° C. to 200 ° C. for a long period of time, the output voltage does not decrease without reducing the oxygen transmission capacity. Can be kept high.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, the effect by the combination along the meaning of this invention is possible, Therefore, this invention is not limited to this Example.

Example 1
The cathode electrode of Example 1 was manufactured as follows. First, 50 ml of a dimethylacetamide solution in which polybenzimidazole (hereinafter referred to as PBI) was dissolved at a concentration of 10% by mass was prepared, 4 g of platinum-supported catalyst was added and mixed, and then dimethylacetamide was removed. . In this way, a mixture of the catalyst and PBI was obtained. The mass ratio of catalyst to PBI was catalyst: PBI = 1: 0.05. As the platinum-supported catalyst, a platinum-supported catalyst (platinum content 40 mass%) in which platinum was supported on carbon (Valcan XC72) was used.
Next, 20 ml of a toluene solution in which poly (1-trimethylsilylpropyne) (hereinafter referred to as PTMSP) is dissolved at a concentration of 2% by mass is prepared, and a mixture of the catalyst and PBI is added to the toluene solution and kneaded. To give a slurry. At this time, the mass ratio of the catalyst to PTMSP was catalyst: PTMSP = 1: 0.05. The obtained slurry was apply | coated on the carbon paper (E-TEK company_made: GDL30BC) which has a fine carbon layer. After coating, the solvent was removed by drying in vacuum at 150 ° C. for about 15 minutes. In this way, the cathode electrode of Example 1 was manufactured. In addition, the compounding ratio of PBI in the cathode electrode was 5% by mass, and the compounding ratio of PTMSP was 2% by mass. The oxygen permeability coefficient of the poly (1-trimethylsilyl-propyne) _{P O2} is at 0% relative humidity conditions 6.0 × ¹⁰ -10 [cm ³ (standard ^{state) · cm / cm 2 · s} · Pa] The molecular weight measured by gel permeation chromatography was 200,000. Furthermore, when the temperature reduction start temperature was measured in a nitrogen atmosphere at a temperature rising rate of 2 ° C./min by thermogravimetric analysis, the weight reduction started at 300 ° C.
The oxygen permeability coefficient _P02 was measured as follows. Poly (1-trimethylsilylpropyne) was formed into a thin film having a thickness of 100 μm, and a measuring apparatus having two regions using this thin film as a partition was prepared. Each region is provided with a gas inflow passage and a gas outflow passage. Ar gas was circulated at a flow rate of 200 ml / L from one inflow passage, and air was circulated at a flow rate of 200 ml / L from the other inflow passage. The oxygen permeation coefficient _P02 was measured by performing a gas component analysis on the region on the side where the Ar gas was flowed using a gas chromatograph.

  Next, a commercially available platinum-supported gas diffusion electrode (Electrochem catalyst electrode EC-20-10-7 manufactured by Electrochem) was prepared as an anode electrode. As an electrolyte, PBI was prepared by doping phosphoric acid with 250 mass% with respect to the basic group of PBI. Then, the fuel cell of Example 1 as shown in FIG. 1 was manufactured by superimposing the cathode electrode, the electrolyte, and the anode electrode, and further disposing the oxidant distribution plate and the fuel distribution plate outside each electrode.

(Example 2)
Next, the cathode electrode of Example 2 was manufactured as follows. First, 10 ml of an N-methylpyrrolidone solution in which polyvinylidene fluoride (hereinafter referred to as PVdF) was dissolved at a concentration of 5% by mass and PBI was dissolved at a concentration of 3% by mass was prepared. 2 g of the same platinum-supported catalyst was added and mixed to prepare a slurry. The mass ratio of the catalyst, PVdF, and PBI was catalyst: PVdF: PBI = 1: 0.05: 0.05.
Next, the obtained slurry was applied on the same carbon paper as in Example 1. After the application, N-methylpyrrolidone was removed by drying in vacuum at 150 ° C. for about 15 minutes. In this way, an electrode layer was formed.
Next, 1 ml of a toluene solution in which PTMSP was dissolved at a concentration of 3 mass% was applied to the obtained electrode layer, and then dried at 150 ° C. for about 15 minutes in vacuum to remove toluene.
In this way, the cathode electrode of Example 2 was manufactured. In addition, the blending ratio of PVdF in the cathode electrode was 5 mass%, the blending ratio of PBI was 3 mass%, and the blending ratio of PTMSP was 2 mass%.
Then, in the same manner as in Example 1, a fuel cell of Example 2 was manufactured using the obtained cathode electrode.

(Comparative Example 1)
A cathode electrode of Comparative Example 1 was produced in the same manner as in Example 2, except that the toluene solution of PTMSP was not applied to the electrode layer. The compounding ratio of PVdF in this cathode electrode was 5% by mass, and the compounding ratio of PBI was 3% by mass. And the fuel cell of the comparative example 1 was manufactured like Example 1 using the obtained cathode electrode.

(Comparative Example 2)
A cathode electrode of Comparative Example 2 was produced in the same manner as in Example 2 except that 1 ml of a toluene solution in which polydimethylsiloxane was dissolved at a concentration of 3% by mass was applied instead of the toluene solution of PTMSP. The blending ratio of PVdF in this cathode electrode was 5 mass%, the blending ratio of PBI was 3 mass%, and the blending ratio of polydimethylsiloxane was 2 mass%. Then, in the same manner as in Example 1, a fuel cell of Comparative Example 2 was manufactured using the obtained cathode electrode. The oxygen permeability coefficient _{P O2} of polydimethylsiloxane was measured in the same manner as in Example 1, the relative humidity of 0% for 6.0 × ¹⁰ -11 [cm ³ (standard state) · cm / cm ² · s · Pa]. The molecular weight measured by gel permeation chromatography was 200,000. Furthermore, when the temperature reduction start temperature was measured in a nitrogen atmosphere at a temperature elevation rate of 2 ° C./min by thermogravimetric analysis, the weight reduction started at 140 ° C.

(Evaluation)
For each fuel cell manufactured as described above, air is supplied to the cathode electrode and hydrogen is supplied to the anode electrode, and the power is generated at an operating temperature of 150.degree. The power generation characteristics were evaluated. Power generation was performed under conditions where the output current density was 0.3 A / cm ² . Table 1 shows the output voltage of each fuel cell when 10 hours, 500 hours, and 1000 hours have elapsed since the start of power generation.

As shown in Table 1, it can be seen that the fuel cells of Examples 1 and 2 maintain a voltage of 0.65 to 0.66 V even after 1000 hours. This is because the activation overvoltage at the cathode is lowered by adding the oxygen permeable resin, and the operating voltage is increased. The output voltage of Example 2 is higher than that of Example 1 because PVdF having oxygen selective solubility is added to the cathode electrode of Example 2, and the oxygen concentration on the catalyst surface becomes higher than that of Example 1. It is thought that it was because of.
On the other hand, in Comparative Examples 1 and 2, since the oxygen permeable resin is not added, the output voltage is reduced to about 0.43 V to 0.63 V after 500 hours. In particular, in Comparative Example 2, measurement is impossible after 1000 hours. This is presumably because the polydimethylsiloxane deteriorated during the continuous operation of the fuel cell because the polydimethylsiloxane had a lower weight starting temperature than poly (1-trimethylsilylpropyne).

It is a schematic diagram which shows the structure of the fuel cell which is embodiment of this invention.

Explanation of symbols

2 ... Cathode electrode, 3 ... Anode electrode, 4 ... Electrolyte, 5 ... Oxidant flow plate, 5a ... Oxidant flow channel, 6 ... Fuel flow plate, 6a ... Fuel flow channel

Claims (4)

A cathode for a fuel cell, comprising a catalyst and an oxygen-permeable resin represented by the following general formula (1).

However, in the above general formula ^(1), R 1 ~R ⁴ are independently an alkyl group, fluorine-substituted alkyl group, those selected from alkylated silyl group, n is an integer of 100 to 10,000 . ^2. The fuel cell according to claim 1, wherein the oxygen permeable resin has an oxygen permeability coefficient PO ₂ of 1 × 10 ⁻¹¹ [cm ³ (standard state) · cm / cm ² · s · Pa] or more. Cathode electrode for use.   The cathode electrode for a fuel cell according to claim 1 or 2, wherein the oxygen permeable resin is poly (1-trimethylsilylpropyne). A fuel cell comprising the cathode electrode for a fuel cell according to any one of claims 1 to 3.

Images