JP5026814B2 - Polymer electrolyte membrane, membrane electrode assembly and fuel cell using the same - Google Patents

Description

  The present invention relates to a novel polymer electrolyte membrane, a membrane electrode assembly using the same, and a fuel cell using the same.

  In recent years, global warming and environmental pollution problems due to mass consumption of fossil fuels have become serious problems. As a means for coping with this problem, a fuel cell using hydrogen as a fuel such as a polymer electrolyte fuel cell (PEFC) is attracting attention instead of an internal combustion engine that burns fossil fuel. In addition, with the advancement of electronic technology, information terminal devices and the like have been downsized year by year, and are rapidly spreading as portable electronic devices. Currently, a fuel cell using methanol as a fuel and a direct methanol fuel cell (DMFC) have been developed as a next-generation power source that compensates for an increase in the amount of information in portable electronic devices and an increase in power consumption associated with high-speed processing.

  Such a fuel cell is mainly composed of a membrane electrode assembly in which electrode catalyst layers serving as an anode and a cathode are arranged on both surfaces of a solid polymer electrolyte membrane. Here, the electrolyte membrane has a role of conducting protons generated by a chemical reaction at the anode to the cathode and a role of separating hydrogen or methanol as a fuel and oxygen as an oxidant. Here, a fluorine-based electrolyte typified by perfluorosulfonic acid has a C—F bond, and therefore has very high chemical stability. For this reason, the fluorine-based electrolyte is applied to the above-mentioned solid polymer electrolyte membrane for fuel cells.

  However, the fluorine-based electrolyte is very expensive because it is specially manufactured. In addition, the halogen compound needs to be adequately addressed to environmental pollution at the time of synthesis and disposal. Therefore, a non-fluorine polymer electrolyte has been desired as an inexpensive and environmentally friendly proton conductor.

  In recent years, as a non-fluorine polymer electrolyte membrane, a resin in which a sulfonic acid group is introduced into an aromatic ring of polysulfone having a specific repeating unit as a proton conductive aromatic polymer membrane that can be produced at low cost is disclosed in Patent Document 1. Proposed.

Patent Document 2 describes a fuel cell and a proton conductive member for a fuel cell using a hybrid electrolyte membrane in which SiO ₂ or P ₂ O ₅ is mixed with a polymer material as an inorganic proton conductive material. Patent Document 3 discloses a hybrid electrolyte containing heteropolyphosphoric acid such as tungstophosphoric acid or molybdophosphoric acid as a proton conductivity imparting agent.

JP-A-9-245818 JP 2002-15742 A JP 2005-89682 A

  When the amount of sulfonic acid introduced is increased in order to increase proton conductivity, the proton-conducting aromatic polymer membrane of Patent Document 1 absorbs water supplied together with water and gas generated by the reaction in the fuel cell power generation environment. As a result, the electrolyte membrane swells and the strength is reduced, and a so-called crossover in which the fuel cross-leaks to the cathode side is caused to greatly reduce the power generation performance. In addition, there is a problem in chemical stability in the fuel cell power generation environment, particularly oxidation resistance on the cathode electrode side, and the durability of the membrane electrode assembly is insufficient.

  An object of the present invention is to provide an electrolyte membrane, a membrane electrode assembly, and a fuel cell using the same, which have improved proton conductivity and oxidation resistance by containing polycarbosilane and a solid inorganic acid in a proton conductive aromatic polymer membrane Is to provide.

  The present invention relates to an ion conductive polymer electrolyte membrane, an ion conductive polymer electrolyte membrane characterized by containing a polymer electrolyte, polycarbosilane dispersed in the polymer electrolyte, and a solid inorganic acid. Comprising an anode electrode having a catalyst layer on one side and a cathode electrode having a catalyst layer on the other side, wherein the ion conductive polymer electrolyte membrane comprises a polymer electrolyte, polycarbosilane dispersed in the polymer electrolyte, and A membrane electrode assembly comprising a solid inorganic acid, and an anode electrode having a catalyst layer on one side of the ion conductive polymer electrolyte membrane and a cathode electrode having a catalyst layer on the other side And a membrane electrode assembly containing polycarbosilane and a solid inorganic acid is used as the ion conductive polymer electrolyte membrane.

  ADVANTAGE OF THE INVENTION According to this invention, the electrolyte membrane and membrane electrode assembly which improved proton conductivity and oxidation resistance, and a fuel cell using the same can be provided.

  It is preferable that the polycarbosilane and the solid inorganic acid are a reaction product in which at least some of them react with each other.

  The polymer electrolyte having a cation exchange group is particularly effective since it has high ion conductivity and is excellent in miscibility or dispersibility with a solid inorganic substance.

  The polymer electrolyte is preferably an aromatic polymer or contains the aromatic polymer. When the aromatic polymer is contained, flexibility and mechanical strength as an electrolyte membrane are improved.

The polycarbosilane is represented by the general formula [(CR ₁ R ₂ ) n-Si (H) R ₃ ] m (wherein R ₁ , R ₂ and R ₃ are hydrocarbon groups having 1 to 20 carbon atoms, n , M is an integer of 1 or more). It is particularly effective to use one or more of polymethylcarbosilane, polyethylcarbosilane, and polyisopropylcarbosilane as the polycarbosilane.

  As the solid inorganic acid, one or more selected from zirconium oxide, tungsten oxide, tungstophosphoric acid, titanium oxide, molybdophosphoric acid, silicon dioxide, phosphoric anhydride, derivatives thereof and precursors thereof can be used. The outermost surface of the solid inorganic acid is considered to have a hydroxyl group or crystal water, and these protons dissociate to show acidity. The solid inorganic acid is dispersed in the polymer and chemically reacts with the polycarbosilane to improve the strength of the matrix of the polymer and impart proton conductivity to the polymer. The solid inorganic acid and polycarbosilane react with each other to form an M—O—Si bond, and thus have proton conductivity. Of the above solid inorganic acids, heteropolyacids are particularly effective.

  In the ion conductive polymer electrolyte membrane, polycarbosilane and an inorganic acid are preferably chemically bonded. The ion conductive polymer electrolyte membrane may contain an aromatic polymer for reinforcing the strength of the electrolyte membrane, and the aromatic polymer may contain an ion exchange group for improving ion conductivity. Furthermore, when an ion exchange group is contained, the dispersibility with the solid inorganic acid is improved.

  Furthermore, as the aromatic polymer according to the present invention, polyethersulfone, polyetheretherketone, polysulfone, polyphenylene sulfide, polyphenylene oxide, polyphenylene and the like excellent in acid hydrolysis resistance are suitable. One or more of these may be mixed and used. Here, the acid hydrolysis resistance means that protons (acids) generated by the reaction in the solid polymer fuel cell are conducted in the electrolyte membrane, and water is generated at the air electrode. Say resistance.

  Moreover, you may mix the said aromatic polymer and another type polymer. In addition, various polycarbosilanes are known as described in JP-A No. 2006-117717, JP-A No. 2006-152063, JP-A No. 2004-359816, and the like. A material in which Si (H) contained therein can react with the solid inorganic acid is used.

  The solid polymer electrolyte preferably has a blending ratio of 1 to 30% by weight of a polymer substance, 1 to 20% by weight of polycarbosilane, and 30 to 95% by weight of a solid inorganic acid. It is particularly preferable that the composition is 20% by weight, 3 to 10% by weight of polycarbosilane, and 60 to 90% by weight of the solid inorganic acid. A mixture of the above composition is dispersed in water or an organic solvent to prepare a varnish.

  The solvent used for electrode formation can be used without particular limitation as long as it can be removed after forming the electrode catalyst layer and does not hinder the dispersion of the carbon support. For example, in addition to water, alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, n-propanol, iso-propyl alcohol, t-butyl alcohol, etc. Alcohol, tetrahydrofuran and the like.

  The catalyst used in the present invention may be any catalyst that promotes the oxidation reaction of the fuel and the reduction reaction of the oxidizing gas. Platinum, gold, silver, palladium, iridium, rhodium, ruthenium, iron, cobalt, nickel, chromium, Metals such as tungsten, manganese, vanadium, alloys, or compounds can be used. Among these, platinum and its alloys are preferable because they are excellent in the effect of promoting the oxidation reaction of fuel and the reduction reaction of oxidizing gas.

  The anode catalyst is preferably a carbon-based powder carrier in which platinum and ruthenium mixed fine particles or platinum-ruthenium alloy fine particles are dispersed and supported, and the cathode catalyst is preferably a carbon-based carrier in which platinum fine particles are dispersed and supported. In addition, the anode and cathode catalysts of the fuel cell of the present invention should use a catalyst to which a third component selected from iron, tin, rare earth elements and the like is further added in order to stabilize and extend the life of the electrode catalyst. preferable.

  The catalyst is preferably used in the form of particles alone or dispersed on a carrier represented by a carbon material. The average particle size of the catalyst at that time is preferably about 1 to 30 nanometers. Examples of the carbon material include carbon black such as furnace black, channel black, and acetylene black, fibrous carbon such as carbon nanotubes, activated carbon, graphite, and the like, and these can be used alone or in combination. .

  The present invention relates to a fuel supply means for supplying fuel to the anode electrode, an oxidizing gas supply means for supplying oxidizing gas to the cathode electrode, a combustion exhaust gas discharging means for discharging combustion gas of the fuel, and an oxidation for discharging exhaust gas of the oxidizing gas In a fuel cell having an exhaust gas discharge means, an ion conductive polymer electrolyte membrane is provided with an anode electrode having a catalyst layer on one surface and a cathode electrode having a catalyst layer on the other surface, the ion conductive polymer electrolyte membrane is A fuel cell using a membrane / electrode assembly containing polycarbosilane and a solid inorganic acid is provided.

  Examples of the fuel supplied to the fuel cell using the membrane electrode assembly according to the present invention include an aqueous methanol solution and hydrogen gas. Examples of the oxidizing gas include oxygen and air containing the same.

  Hereinafter, the present invention will be described in detail by embodiments with reference to the drawings. FIG. 1 is a cross-sectional view of a polymer electrolyte fuel cell to which the present invention is applied. The fuel cell is mainly composed of a membrane electrode assembly according to the present embodiment having an anode electrode 11, a cathode electrode 13, and a proton conductive aromatic polymer membrane 12 sandwiched between them. A fuel 15 mainly composed of hydrogen gas or methanol aqueous solution or the like is supplied to the anode electrode 11 side, and unreacted fuel or exhaust gas 16 is discharged. An oxidizing gas 17 such as oxygen or air is supplied to the cathode electrode 13 side, and an exhaust gas 18 containing unreacted gas in the introduced gas and water is discharged. The anode electrode 11 and the cathode electrode 13 are connected to the external circuit 14.

  The ion conductive electrolyte membrane of Example 1 was produced as follows. As polymethylcarbosilane, SMP-10 manufactured by Starfire was used. Zirconium oxide hydrate, a solid inorganic acid, was synthesized by hydrolyzing zirconium oxychloride in sodium hydroxide. The synthesized zirconium oxide was 2.5 hydrate. This zirconium oxide is dispersed in dimethyl sulfoxide, and polymethylcarbosilane is added thereto and stirred sufficiently. The varnish was produced by dissolving the sulfonated polyethersulfone resin. The varnish was applied and dried at 100 ° C. to 150 ° C. to obtain an electrolyte membrane. As a result, it was confirmed that polymethylcarbosilane and zirconium oxide hydrate, which is a solid inorganic acid, reacted.

  The composition of each material in the electrolyte membrane is polymethylcarbosilane: 5% by weight, zirconium oxide hydrate: 85% by weight, and sulfonated polyethersulfone resin: 10% by weight. This electrolyte membrane was used after being treated in a 1M sulfuric acid aqueous solution at 80 ° C. for 1 hour. This treatment is performed to remove alkali and alkaline earth metal ions such as NaK and Ca due to impurities contained in the electrolyte or invading from the outside, and convert the ion exchange groups into proton bodies.

The membrane electrode assembly of the example was manufactured as follows. 30 g of an Aldrich 5 wt% Nafion solution and 3.0 g of 50 wt% platinum / ruthenium-supported carbon were mixed to form an anode electrode catalyst slurry, which was stirred for 24 hours. The anode electrode catalyst slurry was applied to one surface of the ion conductive electrolyte membrane 12 so that the weight of platinum / ruthenium was 2 mg / cm ² and dried. Similarly to the anode electrode manufacturing method, 30 g of a 5% by weight Nafion solution and 3.0 g of 50% by weight platinum-supported carbon were mixed to form an electrode catalyst slurry for a cathode and stirred for 24 hours. This cathode electrode catalyst slurry was applied to the other surface of the ion conductive electrolyte membrane 12 so that the weight of platinum was 1 mg / cm ² and dried. This was hot-pressed at a pressure of 130 MPa and a temperature of 120 ° C. for 4 minutes to obtain a membrane electrode assembly in this example.

  Further, the membrane electrode assemblies of Examples 1 to 6 and Comparative Examples 1 and 2 were assembled as the fuel cell of FIG. 1, an aqueous solution containing 20% by weight of methanol was supplied to the anode electrode side, and air was supplied to the cathode electrode side. The current-voltage characteristics were measured.

  An ion conductive electrolyte membrane was prepared according to the same procedure as in Example 1. The composition of each material in the manufactured electrolyte membrane is 5% by weight of polymethylcarbosilane, 85% by weight of tungstophosphoric acid, and 10% by weight of polyethersulfone resin. This electrolyte membrane was used after being treated in a 1M sulfuric acid aqueous solution at 80 ° C. for 1 hour.

  The ion conductive electrolyte membrane of Example 3 was prepared in the same manner as in Example 1. The composition of each material in the electrolyte membrane was polymethylcarbosilane: 5% by weight, zirconium oxide hydrate: 65% by weight, and sulfonated. Polyether sulfone resin: 30% by weight. This electrolyte membrane was used after being treated in a 1M sulfuric acid aqueous solution at 80 ° C. for 1 hour.

  The ion conductive electrolyte membrane of Example 4 was produced in the same manner as in Example 1. The composition of each material in the electrolyte membrane was 5% by weight of polymethylcarbosilane, 85% by weight of tungsten oxide, and sulfonated polyethersulfone. Resin: 10% by weight. This electrolyte membrane was used after being treated in a 1M sulfuric acid aqueous solution at 80 ° C. for 1 hour.

  The ion conductive electrolyte membrane of Example 5 was produced in the same manner as in Example 1. The composition of each material in the electrolyte membrane was 5% by weight of polymethylcarbosilane, 85% by weight of tungsten oxide, and sulfonated polyethersulfone. Resin: 10% by weight. This electrolyte membrane was used after being treated in a 1M sulfuric acid aqueous solution at 80 ° C. for 1 hour.

  The ion conductive electrolyte membrane of Example 6 was prepared in the same manner as in Example 1. The composition of each material in the electrolyte membrane was 5% by weight of polymethylcarbosilane, 75% by weight of tungstophosphoric acid, and sulfonated polyether. Sulfone resin: 20% by weight. This electrolyte membrane was used after being treated in a 1M sulfuric acid aqueous solution at 80 ° C. for 1 hour.

(Comparative Example 1)
In Comparative Example 1, Nafion 112 manufactured by DuPont was used as an ion conductive electrolyte membrane without containing a solid inorganic acid and polymethylcarbosilane. The membrane electrode assemblies of Comparative Examples 1 and 2 were produced in the same manner as in the Examples (Comparative Example 2).
In Comparative Example 2, a sulfonated polyethersulfone membrane containing no solid inorganic acid and polymethylcarbosilane was used as the ion conductive electrolyte membrane.

FIG. 2 is a graph showing the relationship between the voltage and current density of the fuel cells according to the examples and comparative examples. The fuel cell using the membrane electrode assembly manufactured using the electrolyte membrane containing the sulfonated polyethersulfone resin of Examples 1 and 3 to 6 and the solid inorganic acid had a current density of 50 mA / cm ^{2 and} was 300 mV or 350 mV or more. It had 50 mV or 180 mV or more at 120 mA / cm ² , and showed higher current-voltage characteristics than those of Comparative Examples 1 and 2.

  On the other hand, the fuel cell of Example 2 using a membrane electrode assembly produced from an electrolyte membrane containing a polyethersulfone resin and a solid inorganic acid has considerably lower characteristics than those of Example 1, but the fuel cell of the comparative example High performance compared to.

  As described above, according to the present example, the addition of the solid inorganic acid and the polycarbosilane improves the proton conductivity and has high voltage-current characteristics, and the fuel cell using the membrane electrode assembly And an ion conductive electrolyte membrane used therefor.

  Since the ion conductive polymer electrolyte according to the present invention is excellent in oxidation resistance and low in cost, it is suitable for a fuel cell membrane electrode assembly, water, hydrohalic acid, salt water electrolyzer, oxygen concentrator, gas sensor, etc. Can be used.

  The present invention can be applied to an electronic device equipped with a fuel cell according to an embodiment of the present invention, a mobile body such as an automobile, an aircraft, a railway, and a distributed power source.

1 is a schematic cross-sectional view of a polymer electrolyte fuel cell to which the present invention is applied. The diagram which shows the relationship between the voltage and current density of a fuel cell.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Anode electrode, 12 ... Ion conductive aromatic polymer membrane, 13 ... Cathode electrode, 14 ... External circuit, 15 ... Fuel, 16 ... Anode discharge, 17 ... Oxidation gas, 18 ... Cathode discharge gas

Claims (21)

  An ion conductive polymer electrolyte membrane comprising a polymer electrolyte, polycarbosilane dispersed in the polymer electrolyte, and a solid inorganic acid.   2. The ion conductive polymer electrolyte membrane according to claim 1, wherein at least a part of the polycarbosilane and the solid inorganic acid react with each other.   The ion conductive polymer electrolyte membrane according to claim 1, wherein the polymer electrolyte has a cation exchange group.   3. The ion conductive polymer electrolyte membrane according to claim 1, wherein the polymer electrolyte is an aromatic polymer or contains the aromatic polymer. The polycarbosilane is represented by the general formula [(CR ₁ R ₂ ) n-Si (H) R ₃ ] m (wherein R ₁ , R ₂ and R ₃ are hydrocarbon groups having 1 to 20 carbon atoms, n , M is an integer of 1 or more). The ion conductive polymer electrolyte membrane according to claim 1 or 2, wherein   6. The ion conductive polymer electrolyte membrane according to claim 1, wherein the polycarbosilane is at least one of polymethylcarbosilane, polyethylcarbosilane, and polyisopropylcarbosilane.   The solid inorganic acid is at least one selected from the group consisting of zirconium oxide, tungsten oxide, tungstophosphoric acid, titanium oxide, molybdophosphoric acid, silicon dioxide, phosphoric anhydride, derivatives thereof and precursors thereof. 3. The ion conductive polymer electrolyte membrane according to 1 or 2.   An ion conductive polymer electrolyte membrane is provided with an anode electrode having a catalyst layer on one side and a cathode electrode having a catalyst layer on the other side, the ion conductive polymer electrolyte membrane comprising a polymer electrolyte and the polymer electrolyte A membrane / electrode assembly comprising polycarbosilane and a solid inorganic acid dispersed in the composition.   9. The membrane electrode assembly according to claim 8, wherein at least a part of the polycarbosilane and the solid inorganic acid react with each other.   9. The membrane electrode assembly according to claim 8, wherein the polymer electrolyte has a cation exchange group.   The membrane electrode assembly according to claim 8 or 10, wherein the polymer electrolyte is an aromatic polymer or contains the aromatic polymer. The polycarbosilane is represented by the general formula [(CR ₁ R ₂ ) n-Si (H) R ₃ ] m (wherein R ₁ , R ₂ and R ₃ are hydrocarbon groups having 1 to 20 carbon atoms, n , M is an integer of 1 or more). The membrane electrode assembly according to claim 8 or 9, wherein   9. The membrane electrode assembly according to claim 8, wherein the polycarbosilane is one or more selected from the group consisting of polymethylcarbosilane, polyethylcarbosilane, and polyisopropylcarbosilane.   The solid inorganic acid is at least one selected from the group consisting of zirconium oxide, tungsten oxide, tungstophosphoric acid, molybdophosphoric acid, titanium oxide, silicon dioxide, phosphoric anhydride, derivatives thereof and precursors thereof. The membrane electrode assembly according to 8 or 9.   An ion conductive polymer electrolyte membrane is provided with an anode electrode having a catalyst layer on one surface and a cathode electrode having a catalyst layer on the other surface, the ion conductive polymer electrolyte membrane comprising polycarbosilane and solid inorganic acid A fuel cell comprising a membrane electrode assembly containing   16. The fuel cell according to claim 15, wherein at least a part of the polycarbosilane and the solid inorganic acid are reacted with each other.   The fuel cell according to claim 15, wherein the polymer electrolyte has a cation exchange group.   18. The fuel cell according to claim 15, wherein the polymer electrolyte contains an aromatic polymer or the aromatic polymer. The polycarbosilane is represented by the general formula [(CR ₁ R ₂ ) n-Si (H) R ₃ ] m (wherein R ₁ , R ₂ and R ₃ are hydrocarbon groups having 1 to 20 carbon atoms, n , M is an integer equal to or greater than 1, and the fuel cell according to claim 15 or 16.   The fuel cell according to any one of claims 15, 16, and 19, wherein the polycarbosilane is at least one selected from the group consisting of polymethylcarbosilane, polyethylcarbosilane, and polyisopropylcarbosilane.   The solid inorganic acid is at least one selected from the group consisting of zirconium oxide, tungsten oxide, tungstophosphoric acid, molybdophosphoric acid, titanium oxide, silicon dioxide, phosphoric anhydride, derivatives thereof and precursors thereof. The fuel cell according to 15 or 16.

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