JP4684935B2 - Cathode electrode for fuel cell and fuel cell - Google Patents

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.

Until now, attempts have been made to reduce the activation overvoltage by using a platinum-based alloy as a catalyst for the cathode electrode, but a sufficient effect has not been obtained.
Therefore, a method has been proposed in which polydimethylsiloxane having excellent oxygen permeability is used as a 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. Therefore, in a fuel cell in which polydimethylsiloxane is added to the cathode electrode, the oxygen permeability of polydimethylsiloxane gradually increases as the operating time becomes longer or the operating temperature becomes higher (120 ° C. to 150 ° C.). There has been a problem that the output voltage gradually decreases due to a drop.
In addition, the use of a fluorine-containing polymer excellent in oxygen solubility and heat resistance as a binder resin has been studied. However, since most of the fluorine-containing polymers are insoluble in a solvent, it is difficult to form an electrode.

  The present invention has been made in view of the above circumstances, and includes a resin material that is excellent in oxygen permeability, heat resistance, and oxidation resistance and that can be dissolved in a solvent as a binder resin to reduce activation overvoltage and durability. An object of the present invention is to provide a cathode electrode for a fuel cell capable of improving the performance and a fuel cell using the same.

In order to achieve the above object, the present invention employs the following configuration.
The fuel cell cathode electrode of the present invention does not contain a catalyst, a fluorine-containing substituted acetylene polymer represented by the following [Chemical Formula 1] , and a silicon-containing substituted acetylene polymer represented by the following [Chemical Formula 2]. The mixing ratio of the fluorine-containing substituted acetylene polymer and the silicon-containing substituted acetylene polymer is a monomer unit in the range of fluorine-substituted acetylene polymer: silicon-containing substituted acetylene polymer = 1: 4 to 1: 100, and The blending ratio of the fluorine-containing substituted acetylene polymer is in the range of 0.01% to 5% by mass, and the blending ratio of the silicon-containing substituted acetylene polymer to the catalyst is in the range of 1% to 20% by mass. and wherein the der Rukoto. However, in the following [Chemical Formula 1] , R ₁ and R ₂ are independently hydrogen, a fluorine group, an alkyl group having 1 to 5 carbon atoms, a fluorine-substituted alkyl group having 1 to 5 carbon atoms , or a fluorine-substituted phenyl group. It is any one of, _{n 1} is Ri integer der of 100 to 10,000, in the following [Chemical Formula _2], R 3 ~R ₅ are each independently alkyl groups of 1 to 5 carbon atoms, carbon atoms Is any one of 1 to 5 fluorine-substituted alkyl groups and fluorine-substituted phenyl groups, and n ₂ is an integer of 100 or more and 10,000 or less.

In the cathode electrode for a fuel cell of the present invention, the oxygen permeability coefficient _{P O2-containing} silicon-substituted acetylene polymer represented by the general formula (2) is 1 × ¹⁰ -11 [cm ³ (standard state) · cm / Cm ² · s · Pa] or more .
Moreover, in the cathode electrode for a fuel cell of the present invention, the fluorine-containing substituted acetylene polymer is preferably poly (2-trifluoromethylphenylacetylene).
Moreover, in the cathode electrode for a fuel cell of the present invention, the silicon-containing substituted acetylene polymer is preferably poly (1-trimethylsilylpropyne).
Moreover, in the cathode electrode for a fuel cell of the present invention, the blending ratio of the fluorine-containing substituted acetylene polymer with respect to the catalyst is preferably in the range of 0.03% to 3% by mass%.
Moreover, in the cathode electrode for a fuel cell of the present invention, the blending ratio of the silicon-containing substituted acetylene polymer with respect to the catalyst is preferably in the range of 3% to 10% by mass%.

  Next, a fuel cell according to the present invention is characterized by including the cathode electrode for a fuel cell as described above.

As described above, according to the cathode electrode for a fuel cell of the present invention, the fluorine-containing substituted acetylene polymer represented by the general formula (1) and the silicon-containing substituted acetylene represented by the general formula (2). Since this fluorine-containing substituted acetylene polymer is excellent in oxygen solubility and heat resistance with respect to the polymer itself, it is possible to increase the oxygen concentration inside the cathode electrode and reduce the activation overvoltage, In addition, sufficient durability can be exhibited even for a long time operation of the fuel cell.
Moreover, this fluorine-containing substituted acetylene polymer can be dissolved in various solvents, and the cathode electrode can be easily formed.

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 general formula (3) as the basic polymer. The average molecular weight of the basic polymer is preferably 1,000 to 1,000,000. 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 fluorine-containing substituted acetylene polymer represented by the formula (4) and the silicon-containing substituted acetylene polymer represented by the following general formula (5) are contained at least. In this catalyst layer 2a, it is desirable that the fluorine-containing substituted acetylene polymer is not in the form of a film but in a form in which the fluorine-containing substituted acetylene polymer is dispersed in the catalyst. Thereby, the fluorine-containing substituted acetylene polymer functions as a binder for the catalyst.

In the following general formula (4), R ₁ and R ₂ are independently any one of hydrogen, a fluorine group, an alkyl group, a fluorine-substituted alkyl group, and a fluorine-substituted phenyl group, and n ₁ is 100 or more. It is an integer of 10,000 or less. R ₁ and R ₂ are independently hydrogen, a fluorine group, an alkyl group having 1 to 5 carbon atoms, a fluorine-substituted alkyl group having 1 to 5 carbon atoms, or 5 hydrogen atoms of a phenyl group. More preferably, it is any one of fluorine-substituted phenyl groups in which one or two of them are substituted with fluorine atoms, R ₁ is hydrogen, and R ₂ is a trifluoromethyl group (CF ₃ group). 2-trifluoromethylphenylacetylene) is most preferred.

The fluorine-containing substituted acetylene polymer represented by the general formula (4) is a resin obtained by replacing the hydrogen of polyacetylene with a phenyl group having an R ₁ group and an R ₂ group. Since this fluorine-containing substituted acetylene polymer has a main chain of a polyacetylene structure, it has high heat resistance and oxidation resistance. For example, it does not decompose even in an oxidizing atmosphere of 150 ° C. or higher.
Further, this fluorine-containing substituted acetylene polymer has a high solubility of oxygen in the polymer, and particularly has a property of selectively dissolving oxygen in the air. Therefore, by containing the fluorine-containing substituted acetylene polymer in the cathode electrode, the oxygen concentration in the catalyst layer 2a is improved, and the activation overvoltage is reduced. Furthermore, even though the fluorine-containing substituted acetylene polymer is a fluorine-based resin, it exhibits solubility in solvents such as toluene, so that a uniform slurry is formed by mixing with a solvent together with a catalyst. By forming the cathode electrode, the fluorine-containing substituted acetylene polymer can be uniformly dispersed in the catalyst layer 2a.
From the above, the fluorine-containing substituted acetylene polymer is suitable as an electrode constituent material for a fuel cell.

The silicon- containing substituted acetylene polymer is desirably contained in the cathode electrode in a state of being dispersed in the catalyst in the same manner as the fluorine-containing substituted acetylene polymer. Thus, the silicon-containing substituted acetylene polymer also functions as a catalyst binder.

In the following general formula (5), R _{3 to} R ₅ are independently any one of an alkyl group, a fluorine-substituted alkyl group, and a fluorine-substituted phenyl group, and n ₂ is an integer of 100 or more and 10,000 or less. is there. R _{3 to} R ₅ are independently 1 to 2 of 5 hydrogen atoms of an alkyl group having 1 to 5 carbon atoms, a fluorine-substituted alkyl group having 1 to 5 carbon atoms, or a phenyl group. more preferably the are those selected from fluorine-substituted phenyl group substituted with a fluorine atom, more preferably R ₃ to R ₅ are independently a carbon number of 1 to 3 alkyl groups, R ₃ ~ Particularly preferred is poly (1-trimethylsilylpropyne) in which all R ₅ are methyl groups.

The silicon-containing substituted acetylene polymer represented by the above general formula (5) is a resin in which hydrogen of polyacetylene is substituted with the above R _{3 to} R ₅ substituted silyl group. Since this silicon-containing substituted acetylene polymer has a main chain of a polyacetylene structure, it has high heat resistance and oxidation resistance, and does not decompose even in an oxidizing atmosphere of 200 ° C. or higher. That is, this silicon-containing substituted acetylene polymer has an excellent heat resistance with a weight reduction starting temperature of 200 ° C. or higher when the weight reduction starting temperature is measured by thermogravimetric analysis. In particular, poly (1-trimethylsilylpropyne) has a weight reduction starting temperature of 300 ° C. or higher, and has heat resistance suitable as an electrode constituent material of a fuel cell operating at about 80 ° C. to 200 ° C.

In addition, this silicon-containing substituted acetylene polymer has R _{3 to} R ₅ substituted silyl groups having high mobility between the extended main chains. The silicon-containing acetylene polymer having such a molecular structure has an oxygen permeability of 10 times or more compared to conventional polydimethylsiloxane and the like. Therefore, by containing the silicon-containing substituted acetylene polymer in the cathode electrode, the oxygen concentration on the catalyst surface is improved, and the activation overvoltage is reduced.
Furthermore, since the silicon-containing substituted acetylene polymer has high solubility in a solvent such as toluene, it can be uniformly dispersed in the catalyst layer 2a as in the case of the fluorine-containing substituted acetylene polymer.
From the above, the silicon-containing substituted acetylene polymer is suitable as an electrode constituent material of a fuel cell, like the fluorine-containing substituted acetylene polymer.

The oxygen-containing coefficient P _O2 of the silicon-containing substituted acetylene polymer is 1 × 10 ⁻¹¹ [cm ³ (standard state) · cm / cm ² · s · Pa] or more, more preferably 1 × 10 ⁻¹⁰ [cm. ³ (standard state) · cm / cm ² · s · Pa] or more. The most preferable poly (1-trimethylsilylpropyne) as the silicon-containing substituted acetylene polymer has an oxygen permeability coefficient P _O2 of 1 × 10 ⁻¹⁰ to 1 × 10 ⁻⁹ [cm ³ (standard state) · cm / cm ² · s · Pa] grade. 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. .

By the way, since the fluorine-containing substituted acetylene polymer has a relatively high oxygen / nitrogen separation coefficient (P _O2 / P _N2 ), the selective solubility of oxygen in the polymer is high, but the oxygen permeability coefficient P _O2 itself. Is lower than that of silicon-containing substituted acetylene polymers, and therefore has a property that the permeation amount of oxygen itself is small.
Therefore, in the cathode electrode according to the present invention, in addition to the fluorinated substituent acetylene polymers, the oxygen permeability coefficient P _O2 is Ru contain a relatively high silicon-containing substituted acetylene polymer. As a result, the oxygen permeability coefficient P _O2 and the oxygen / nitrogen separation coefficient (P _O2 / P _N2 ) of the binder in the cathode electrode are improved, so that the oxygen concentration in the catalyst layer can be improved and the oxygen concentration on the catalyst surface is also improved. This can further reduce the activation overvoltage.

The mixing ratio of the fluorine-containing substituted acetylene polymer and the silicon-containing substituted acetylene polymer in the cathode electrode is preferably in the range of monomer units and fluorine-substituted acetylene polymer: silicon-containing substituted acetylene polymer = 1: 4 to 1: 100. When the mixing ratio of the two polymers is 1: 4 or more, the content of the silicon-containing substituted acetylene polymer is sufficient, and the oxygen permeability coefficient _PO2 of the binder in the cathode electrode can be improved. Further, when the mixing ratio of the two polymers is 1: 100 or less, the content of the fluorine-containing substituted acetylene polymer becomes a sufficient amount, and the oxygen / nitrogen separation factor ( _PO2 / _PN2 ) of the binder in the cathode electrode can be improved. .

Further, the blending ratio of the fluorine-containing substituted acetylene polymer with respect to the catalyst is preferably in the range of 0.01% to 5% by mass%, more preferably in the range of 0.03% to 3%. Furthermore, the blending ratio of the silicon-containing substituted acetylene polymer with respect to the catalyst is preferably in the range of 1% to 20% by mass, more preferably in the range of 3% to 10%.
If the blending ratio of each polymer with respect to the catalyst is not less than the lower limit value, a sufficient amount of oxygen can be supplied to the catalyst surface. If the blending ratio is equal to or less than the upper limit value, the resistivity of the cathode electrode 2 itself can be kept low, and the internal resistance of the cathode electrode can be reduced.

The catalyst layer 2a of the cathode electrode 2 has a basic polymer or proton conductive resin capable of retaining a hydrophobic resin, phosphoric acid, etc. in addition to a catalyst, a fluorine-containing substituted acetylene polymer, and a silicon- containing substituted acetylene polymer. Any of these may be added. 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 produce the catalyst layer 2a, for example, a catalyst, a fluorine-containing substituted acetylene polymer, and a silicon- containing substituted acetylene polymer are mixed in an appropriate solvent to form a slurry, and this slurry is formed into the porous carbon sheet 2b. It can be produced by coating and further removing the solvent. A hydrophobic resin, a basic polymer, or a proton conductive resin may be added to the slurry. As the solvent, for example, toluene can be used. By using toluene, at least the fluorine-containing substituted acetylene polymer and the silicon-containing substituted acetylene polymer can be dissolved.
Further, when the hydrophobic resin, basic polymer or proton conductive resin is insoluble in a solvent such as toluene, a catalyst layer is formed with these hydrophobic resin or the like and a catalyst, and then the fluorine-containing substituted acetylene polymer is formed. Simultaneously with the addition, a silicon- containing substituted acetylene polymer may be added. 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 fluorine-containing substituted acetylene polymer and the silicon- containing substituted acetylene polymer are dissolved is prepared, and the mixture is added to the toluene solution and kneaded to form a slurry. The catalyst layer is formed by applying to the sheet 2b and further removing toluene. 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 is further 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 1,000 to 1,000,000. 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 1000000 or more, it is difficult to dissolve in the solvent and mixing with the catalyst becomes difficult.

  The fluorine-containing substituted acetylene polymer contained in the cathode electrode 2 according to the present invention is excellent in selective solubility for selectively dissolving oxygen, can withstand high temperatures of about 200 ° C., and is excellent in oxidation resistance. Is. A part of the oxygen supplied from the oxidant channel 5a to the cathode electrode 2 is absorbed by the porous catalyst layer 2a and reaches the catalyst surface, while the other part permeates the fluorine-containing substituted acetylene polymer. To reach the catalyst surface. As described above, according to the cathode electrode 2 of the present embodiment, by containing the fluorine-containing substituted acetylene polymer, the oxygen concentration in the catalyst layer 2a 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.

Further, by adding a silicon-containing substituted acetylene polymer to the cathode electrode 2 in addition to the fluorine-containing substituted acetylene polymer, the oxygen permeation coefficient P _O2 and oxygen / nitrogen separation coefficient (P _O2 / P _N2 ) of the binder at the cathode electrode Both improve, the oxygen concentration inside the catalyst layer 2a improves, and at the same time the oxygen concentration on the catalyst surface can be increased, and the activation overvoltage can be further reduced.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to this Example.

( Reference Example 1)
The cathode electrode of Reference Example 1 was produced as follows. First, 20 ml of a toluene solution in which poly (2-trifluoromethylphenylacetylene) (hereinafter referred to as PTFMPA) was dissolved at a concentration of 0.3% by mass was prepared, and 2 g of a platinum-supported catalyst was added to the toluene solution. To make a slurry. The mass ratio of catalyst to PTFMPA was catalyst: PTFMPA = 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.
The obtained slurry was applied on carbon paper (SGL Carbon: GDL30BC) having a fine carbon layer. After coating, the solvent was removed by drying in vacuum at 150 ° C. for about 15 minutes. Thus, the cathode electrode of Reference Example 1 in which the catalyst layer was formed on the carbon paper was produced. In addition, the compounding ratio of PTFMPA in the catalyst layer of the cathode electrode was 5% by mass.

The oxygen permeability coefficient _{P O2} of PTFMPA is at 0% relative humidity conditions 2.5 × ¹⁰ -9 [cm ³ (standard ^{state) · cm / cm 2 · s} · Pa], the oxygen diffusion coefficient (D) Is 4.0 × 10 ⁻⁷ [cm ² / s], the oxygen solubility coefficient (S) is 4.73 × 10 ⁻⁶ [cm ³ (standard state) / cm ³ · Pa], and oxygen / nitrogen The separation factor ( _PO2 / _PN2 ) was 3.4, and the molecular weight measured by gel permeation chromatography was 160000.
The oxygen permeability coefficient _P02 was measured as follows. PTFMPA 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. Further, as an electrolyte, a PBI film in which phosphoric acid was doped with 300% by mass with respect to a basic group of polybenzimidazole (hereinafter referred to as PBI) was prepared. Then, a fuel cell of Reference Example 1 as shown in FIG. 1 was manufactured by superimposing the cathode electrode, the electrolyte, and the anode electrode, and disposing an oxidant distribution plate and a fuel distribution plate outside each electrode.

(Example 2)
The cathode electrode of Example 2 was manufactured as follows. First, toluene obtained by dissolving PTFMPA and poly (1-trimethylsilylpropyne) (hereinafter referred to as PTMSP) at a monomer unit ratio (PTFMPA: PTMSP) of 1: 4 and a concentration of 0.5% by mass. 20 ml of a solution was prepared, and 2 g of a platinum-supported catalyst was added to the toluene solution and mixed to form a slurry. The mass ratio of the catalyst, PTFMPA, and PTMSP was catalyst: (PTFMMPA + PTMSP) = 1: 0.05. The same platinum-supported catalyst as in Reference Example 1 was used.
The obtained slurry was applied on the same type of carbon paper as in Reference Example 1. 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 2 was manufactured.
A fuel cell of Example 2 was manufactured in the same manner as Reference Example 1 except that the cathode electrode of Example 2 was used. In addition, the compounding rate of PTFMPA in the catalyst layer of a cathode electrode was 1 mass%, and the compounding rate of PTMSP was 4 mass%.

The oxygen permeability coefficient P _O2 of PTMSP is 7.9 × 10 ⁻⁷ [cm ³ (standard state) · cm / cm ² · s · Pa] under the condition of 0% relative humidity, and the oxygen diffusion coefficient (D) Is 4.0 × 10 ⁻⁵ [cm ² / s], the oxygen solubility coefficient (S) is 1.5 × 10 ⁻⁵ [cm ³ (standard state) / cm ³ · Pa], and oxygen / nitrogen The separation factor (P _O2 / P _N2 ) was 1.6, and the molecular weight measured by gel permeation chromatography was 180000. The oxygen permeability coefficient PO ₂ was measured in the same manner as in Reference Example 1.

(Example 3)
A cathode electrode of Example 3 was produced in the same manner as in Example 2 except that the monomer unit ratio of PTFMPA and PTMSP (PTFMMPA: PTMSP) was 1: 100.
A fuel cell of Example 3 was manufactured in the same manner as Reference Example 1 except that the cathode electrode of Example 3 was used. The PTFMPA content in the catalyst layer of the cathode electrode was 0.05% by mass, and the PTMSP content was 5% by mass.

Example 4
A cathode electrode of Example 4 was produced in the same manner as in Example 2 except that the monomer unit ratio of PTFMPA and PTMSP (PTFMMPA: PTMSP) was 1: 200.
And the fuel cell of Example 4 was manufactured like the reference example 1 except having used the cathode electrode of Example 4. FIG. In addition, the compounding rate of PTFMPA in the catalyst layer of the cathode electrode was 0.03% by mass, and the compounding rate of PTMSP was 5% by mass.

(Comparative Example 1)
20 ml of N-methylpyrrolidone solution (NMP solution) in which poly (vinylidene fluoride) (hereinafter referred to as PVdF) is dissolved at a concentration of 0.3% by mass is prepared, and 2 g of a platinum-supported catalyst is added to the NMP solution. And mixed to make a slurry. The mass ratio of catalyst to PVdF was catalyst: PVdF = 1: 0.05. In addition, the platinum supported catalyst similar to the reference example 1 was used for the platinum supported catalyst.
The obtained slurry was applied on the same type of carbon paper as in Reference Example 1. After coating, the solvent was removed by drying in vacuum at 150 ° C. for about 15 minutes. In this way, the cathode electrode of Comparative Example 1 was produced. The blending ratio of PVdF in the catalyst layer of the cathode electrode was 3% by mass.
And the fuel cell of the comparative example 1 was manufactured like the reference example 1 except having used the cathode electrode of the comparative example 1. FIG.

(Comparative Example 2)
A fuel cell of Comparative Example 2 was produced in the same manner as Reference Example 1 except that PTMSP was used instead of PTFMPA.

(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 power generation is performed under conditions where the operating temperature is 150 ° C. and the electrolyte is not humidified (non-humidified condition). 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, the fuel cell of Reference Example 1 maintains a voltage of 0.605 V even after 1000 hours, and maintains a higher output voltage than that of Comparative Example 1. I understand. This is because the oxygen concentration inside the catalyst layer of the cathode electrode is increased and the activation overvoltage is lowered due to the inclusion of PTFMPA having high oxygen solubility, thereby increasing the operating voltage.
In the fuel cells of Examples 2 and 3, it can be seen that the inclusion of PTMSP having high oxygen permeability in addition to PTFMPA increases the oxygen concentration on the catalyst surface and further increases the output voltage.
The fuel cells of Reference Example 1, Example 2, and Example 3 had lower output voltages after 10 hours than Comparative Example 2 that did not contain PTFMPA, but after 500 hours, Reference Example 1 and Example 2 and the output voltage of Example 3 were larger than those of Comparative Example 2, and the output voltage hardly decreased between 500 hours and 1000 hours. This is because inclusion of PTFMPA improved the heat resistance and oxidation resistance of the cathode electrode and improved the long-term stability of the fuel cell.
About Example 4, since the content rate of PTFMPA is low, the output voltage after 500 to 1000 hours is lower than that of Reference Example 1, Example 2, and Example 3 , but the output after 10 hours. It can be seen that the voltage is the highest among Reference Example 1, Example 2, Example 3, and Comparative Examples 1 and 2, and the initial characteristics are excellent.

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 (7)

A catalyst, a fluorinated substituent acetylene polymer represented by the following Formula 1], Ri name contains a silicon-containing substituent acetylene polymer represented by the following Formula 2], wherein said fluorine-substituted acetylene polymer containing The mixing ratio of the silicon-substituted acetylene polymer is in the range of monomer units, fluorine-substituted acetylene polymer: silicon-containing substituted acetylene polymer = 1: 4 to 1: 100, and the blending ratio of the fluorine-containing substituted acetylene polymer with respect to the catalyst is mass. % in the range of less than 5% 0.01%, the fuel cell content ratio of the silicon-containing substituent acetylene polymer to said catalyst and wherein the range der Rukoto 20% less than 1% by weight% Cathode electrode.
However, in the following [Chemical Formula 1] , R ₁ and R ₂ are independently hydrogen, a fluorine group, an alkyl group having 1 to 5 carbon atoms, a fluorine-substituted alkyl group having 1 to 5 carbon atoms , or a fluorine-substituted phenyl group. It is any one of, _{n 1} is Ri integer der of 100 to 10,000, in the following [Chemical Formula _2], R 3 ~R ₅ are each independently alkyl groups of 1 to 5 carbon atoms, carbon atoms Is any one of 1 to 5 fluorine-substituted alkyl groups and fluorine-substituted phenyl groups, and n ₂ is an integer of 100 or more and 10,000 or less.

The oxygen permeation coefficient P _O2 of the silicon-containing substituted acetylene polymer represented by the above [Chemical Formula 2] is 1 × 10 ⁻¹¹ [cm ³ (standard state) · cm / cm ² · s · Pa] or more. The cathode electrode for a fuel cell according to claim 1 . The cathode electrode for a fuel cell according to claim 1 or 2 , wherein the fluorine-containing substituted acetylene polymer is poly (2-trifluoromethylphenylacetylene). 4. The cathode electrode for a fuel cell according to any one of claims 1 to 3 , wherein the silicon-containing substituted acetylene polymer is poly (1-trimethylsilylpropyne). 5. The fuel cell according to claim 1, wherein a blending ratio of the fluorine-containing substituted acetylene polymer with respect to the catalyst is in a range of 0.03% to 3% by mass%. Cathode electrode. 6. The cathode electrode for a fuel cell according to claim 1, wherein a blending ratio of the silicon-containing substituted acetylene polymer to the catalyst is in a range of 3% to 10% by mass%. .   A fuel cell comprising the cathode electrode for a fuel cell according to any one of claims 1 to 6.

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