Conductive titanium oxide, metal-supported conductive titanium oxide, film electrode assembly, polymer electrolyte fuel cell, method for producing conductive titanium oxide, and method for producing metal-supported conductive titanium oxide

Abstract

The present invention addresses the problem of suppressing any lowering of durability in a carrier of a catalyst layer. This electroconductive titanium oxide has an electroconductivity of 0.1 S / cm or greater as measured under a pressure of 10 MPa.

Description

[Technical Field]

[0001] The present invention relates to conductive titanium oxide, metal-supported conductive titanium oxide, membrane electrode assembly, polymer electrolyte fuel cell, method for producing conductive titanium oxide, and method for producing metal-supported conductive titanium oxide. [Background technology]

[0002] A polymer electrolyte fuel cell comprises a membrane electrode assembly having a polymer electrolyte layer and a pair of catalyst layers bonded to the polymer electrolyte layer. Furthermore, the polymer electrolyte fuel cell comprises a pair of gas diffusion layers and a pair of separators.

[0003] Generally, the gas diffusion layer is composed of a porous carbon material, and the separator is composed of a metallic material. The catalyst layer has a structure in which noble metal nanoparticles, such as Pt, are supported on the surface of a support. Carbon materials are commonly used as the support.

[0004] Patent Document 1 describes using a fluorine-based polymer such as Nafion® in the solid polymer electrolyte layer of a membrane electrode assembly. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2016-219179 [Overview of the project] [Problems that the invention aims to solve]

[0006] Incidentally, since fluorinated polymers are superacidic solid acids, membrane electrode assemblies using fluorinated polymers may be used under superacidic conditions. Also, while the cell voltage of a polymer electrolyte fuel cell is 0.4 to 1.0V during normal operation, the cell voltage may rise to 1.5V during startup and shutdown. Therefore, there was a risk that the carbon material in the catalyst layer would be electrochemically oxidized and decomposed into CO2. This decomposition reaction of the carbon material could reduce the durability of the support material. [Means for solving the problem]

[0007] To solve the above problem, the conductive titanium oxide must have an electrical conductivity of 0.1 S / cm or higher, as measured under a pressure of 10 MPa. Regarding the conductive titanium oxide mentioned above, the specific surface area is 100 m². 2 It is preferable that the amount is 1 / g or more.

[0008] The essence of the metal-supported conductive titanium oxide for solving the above problems is that it comprises the conductive titanium oxide and metal particles supported on the conductive titanium oxide. The membrane electrode assembly for solving the above problems comprises a solid polymer electrolyte layer and a pair of catalyst layers bonded to the solid polymer electrolyte layer, wherein at least one of the pair of catalyst layers contains the metal-supported conductive titanium oxide.

[0009] The polymer electrolyte fuel cell designed to solve the above problems comprises the membrane electrode assembly, a pair of gas diffusion layers, and a pair of separators. The method for producing conductive titanium oxide to solve the above problems comprises a gelation step of gelling a solution containing a titanium source and a carbon source; a drying step of drying the gel obtained in the gelation step at a temperature of 105°C to 200°C to produce a dried body; and a heating step of heating the dried body at a temperature of 800°C to 1200°C in a hydrogen-containing atmosphere.

[0010] The manufacturing method of the metal-supported conductive titanium oxide for solving the above problems includes a dispersion step of dispersing the conductive titanium oxide produced by the manufacturing method of the above conductive titanium oxide and a metal solution in an organic solvent having a hydroxyl group to prepare a dispersion liquid, and a supporting step of heating the dispersion liquid to support the metal contained in the metal solution on the conductive titanium oxide. The gist is that it has these steps.

Effects of the Invention

[0011] According to the present invention, it is possible to suppress a decrease in durability in the carrier of the catalyst layer.

Brief Description of the Drawings

[0012] [Figure 1] It is an exploded perspective view of the solid polymer fuel cell of the present embodiment. [Figure 2] It is an X-ray diffraction pattern of the conductive titanium oxide of the present embodiment. [Figure 3] It is an X-ray diffraction pattern of another conductive titanium oxide of the present embodiment. [Figure 4] It is an X-ray diffraction pattern of yet another conductive titanium oxide of the present embodiment. [Figure 5] It is a graph showing the measurement results of the powder conductivity of the conductive titanium oxide. [Figure 6] It is an adsorption isotherm of the conductive titanium oxide of the present embodiment. [Figure 7] It is a graph showing the power generation characteristics of a single cell using a membrane electrode assembly. [Figure 8] It is a graph showing the power generation characteristics of a single cell using another membrane electrode assembly. [Figure 9] It is a graph showing the results of an accelerated degradation test of a single cell using the membrane electrode assembly of the present embodiment.

Modes for Carrying Out the Invention

[0013] This document describes embodiments of the conductive titanium oxide, metal-supported conductive titanium oxide, film electrode assembly, polymer electrolyte fuel cell, method for producing conductive titanium oxide, and method for producing metal-supported conductive titanium oxide according to the present invention.

[0014] [Polymer electrolyte fuel cell] As shown in Figure 1, the polymer electrolyte fuel cell (hereinafter also referred to as "PEFC") 20 comprises a membrane electrode assembly (hereinafter also referred to as "MEA") 10 having a solid polymer electrolyte layer 11 and a pair of catalyst layers 12 bonded to the solid polymer electrolyte layer 11. One of the pair of catalyst layers 12 constitutes the anode-side electrode catalyst layer 12A, and the other constitutes the cathode-side electrode catalyst layer 12C.

[0015] Furthermore, the PEFC20 comprises a pair of gaskets 13, a pair of gas diffusion layers (hereinafter also referred to as "GDL") 21, and a pair of separators 22. The catalyst layer 12 has a structure in which an electrode catalyst is supported on the surface of a support. The conductive titanium oxide of the present invention can be used as a support for the catalyst layer 12. The metal-supported conductive titanium oxide of the present invention can be used as the anode-side electrode catalyst layer 12A of the pair of catalyst layers 12 described above. Alternatively, it can be used as the cathode-side electrode catalyst layer 12C. It can also be used as both the anode-side electrode catalyst layer 12A and the cathode-side electrode catalyst layer 12C.

[0016] The following describes each component that makes up PEFC20. [Solid polymer electrolyte layer] As shown in Figure 1, the solid polymer electrolyte layer 11 is a solid polymer film that has proton conductivity.

[0017] The material of the solid polymer electrolyte layer 11 is not particularly limited, and fluorine-based polymer electrolytes or hydrocarbon-based polymer electrolytes can be used. Specific examples of fluorine-based polymer electrolytes include, for example, Nafion® manufactured by DuPont, FLMION® manufactured by Asahi Glass Co., Ltd., ACIPLEX® manufactured by Asahi Kasei Corporation, and GORE-SELECT® manufactured by Gore.

[0018] Examples of hydrocarbon polymer electrolyte membranes include sulfonated polyether ketones, sulfonated polyethersulfones, sulfonated polyetherethersulfones, sulfonated polysulfides, and sulfonated polyphenylenes.

[0019] As shown in Figure 1, the solid polymer electrolyte layer 11 has a pair of surfaces. An anode-side electrode catalyst layer 12A is bonded to one of these surfaces. A cathode-side electrode catalyst layer 12C is bonded to the other surface. In other words, a pair of catalyst layers 12, consisting of an anode-side electrode catalyst layer 12A and a cathode-side electrode catalyst layer 12C, are bonded to both sides of the solid polymer electrolyte layer 11. The MEA 10 is formed by bonding the pair of catalyst layers 12 to both sides of the solid polymer electrolyte layer 11.

[0020] In the solid polymer electrolyte layer 11, the surface to which the cathode-side electrode catalyst layer 12C is bonded is the cathode surface, and the surface to which the anode-side electrode catalyst layer 12A is bonded is the anode surface. [Catalyst layer] As shown in Figure 1, the pair of catalyst layers 12 consists of an anode-side electrode catalyst layer 12A and a cathode-side electrode catalyst layer 12C. Each of the pair of catalyst layers 12 has a support and an electrode catalyst supported on the surface of the support.

[0021] (carrier) The support is composed of conductive titanium oxide. Specifically, the support is formed in a film-like structure by the aggregation of multiple particulate conductive titanium oxide particles.

[0022] Conductive titanium oxide exhibits an electrical conductivity of 0.1 S / cm or higher when measured under a pressure of 10 MPa. The conductive titanium oxide is preferably of a conductivity of 1 S / cm or higher, as measured under a pressure of 10 MPa.

[0023] Because the conductivity of the conductive titanium oxide falls within the above numerical range, the conductive titanium oxide exhibits conductivity comparable to that of graphite. Therefore, it can be used as a substitute for carbon materials, which are commonly used as supports for the catalyst layer 12. Since conductive titanium oxide has excellent durability, using it as a support for the catalyst layer 12 effectively suppresses the deterioration of the support's durability. The method for measuring conductivity will be described later.

[0024] Conductive titanium oxide has a specific surface area of ​​100 m². 2 It is preferable that the amount be 1 / g or more, and the specific surface area be 150 m². 2 It is more preferable that the amount be 1 / g or more. Because the specific surface area is within the above numerical range, the amount of electrode catalyst that can be supported can be relatively increased. Therefore, when used in the catalyst layer 12 of a polymer electrolyte fuel cell 20, it can contribute to improving the power generation performance.

[0025] The method for measuring the specific surface area is not particularly limited, but for example, it can be measured by a gas adsorption method, also known as the BET method, using nitrogen (N2) as the adsorbed molecule. The particle size of the conductive titanium oxide is not particularly limited, but it is preferable that the average particle size be 500 nm or less, and more preferably 100 nm or less.

[0026] By having the average particle size of conductive titanium oxide within the above numerical range, the specific surface area of ​​the carrier can be relatively increased. The method for measuring the average particle size of conductive titanium oxide is not particularly limited, but for example, it can be measured by observing multiple particles with an electron microscope, measuring their particle sizes, and calculating the average value.

[0027] The crystal structure of the conductive titanium oxide is not particularly limited, and may be, for example, the rutile type structure of TiO2 or the corundum type structure of Ti2O3. Also, Ti n O 2n-1 (n = 4 to 9) may have a Magnéli phase having a composition, or may have a composition of Ti3O5. Among these, those having a Magnéli phase or a composition of Ti3O5 are preferable because a high conductivity is easily obtained. Further, those having a Magnéli phase are preferable because a higher conductivity is easily obtained.

[0028] Also, the conductive titanium oxide is preferably composed of a single phase. The method for measuring the crystal structure of the conductive titanium oxide is not particularly limited, but can be measured, for example, by using a known X-ray diffractometer (hereinafter also referred to as "XRD diffractometer").

[0029] [3]] The carrier may contain a material other than the above conductive titanium oxide within a range where the effects of the present invention can be achieved. Examples of the material other than the conductive titanium oxide include carbon materials such as graphite.

[0030] (Electrode catalyst) The electrode catalyst is a catalyst for promoting the oxidation-reduction reaction in each catalyst layer 12. At the cathode, it promotes the oxygen reduction reaction represented by the following formula (1). At the anode, it promotes the hydrogen oxidation reaction represented by the following formula (2).

[0031] ? 4H + +O2+4e - →2H2O ··· Formula (1) H2→2H + +2e - ··· Formula (2) Note that the above oxidation-reduction reaction is also referred to as an electrochemical reaction.

[0032] The type of the electrode catalyst is not particularly limited, and any of noble metal-based catalysts and non-noble metal-based catalysts can be used as long as they have electrochemical catalytic activity. Specific examples of electrode catalysts include precious metals such as platinum (Pt), ruthenium (Ru), iridium (Ir), palladium (Pd), rhodium (Rh), osmium (Os), gold (Au), and silver (Ag), as well as alloys containing these precious metals. Other examples include tantalum (Ta), zirconium (Zr), titanium (Ti), molybdenum (Mo), chromium (Cr), cobalt (Co), and iron (Fe).

[0033] The amount of electrode catalyst supported is not particularly limited, but it is preferably 10% by mass or more, and more preferably 15% by mass or more, relative to the sum of the mass of the electrode catalyst and the mass of the catalyst support. [gasket] As shown in Figure 1, the cathode-side electrode catalyst layer 12C and the anode-side electrode catalyst layer 12A are configured to be slightly smaller than the solid polymer electrolyte layer 11 and are bonded to the inside of the outer edge of the solid polymer electrolyte layer 11.

[0034] On the anode surface of the solid polymer electrolyte layer 11, the anode-side gasket 13A is positioned as one of a pair of gaskets 13 in the outer periphery not covered by the anode-side electrode catalyst layer 12A.

[0035] On the cathode surface of the solid polymer electrolyte layer 11, the cathode-side gasket 13C is positioned as the other of a pair of gaskets 13 in the outer periphery not covered by the cathode-side electrode catalyst layer 12C.

[0036] The material constituting the gasket 13 is not particularly limited, but for example, a fluororesin can be used. Specifically, a fluororesin film can be used. The placement of the cathode-side gasket 13C and the anode-side gasket 13A suppresses gas leakage from the outer periphery of the solid polymer electrolyte layer 11.

[0037] [GDL] As shown in Figure 1, a pair of GDLs 21 are arranged on both sides of the MEA 10. The cathode-side gas diffusion layer (hereinafter also referred to as "cathode-side GDL") 21C is positioned in contact with the cathode-side electrode catalyst layer 12C of the MEA 10. The anode-side gas diffusion layer (hereinafter also referred to as "anode-side GDL") 21A is positioned in contact with the anode-side electrode catalyst layer 12A of the MEA 10.

[0038] A pair of GDL21s are composed of a material that has gas diffusivity and conductivity. The material constituting the GDL21 is not particularly limited, but examples include porous carbon materials such as carbon cloth, carbon paper, and nonwoven fabrics.

[0039] The cathode electrode catalyst layer 12C and the cathode GDL 21C form the cathode 20C, also called the air electrode. The anode electrode catalyst layer 12A and the anode GDL 21A form the anode 20A, also called the fuel electrode. A single cell is formed by arranging the cathode GDL 21C and the anode GDL 21A in the MEA 10.

[0040] [Separator] As shown in Figure 1, the pair of separators 22 are positioned outside the GDL21 located on both sides of the MEA10. The separator 22 located on the cathode side GDL21C is called the cathode side separator 22C. The separator 22 located on the anode side GDL21A is called the anode side separator 22A.

[0041] Each pair of separators 22 has multiple grooves on both sides. The groove 22Cg on the GDL21C side of the cathode-side separator 22C functions as a passage for oxidizing gases such as air. The groove 22Cw on the opposite side from the GDL21 side functions as a passage for cooling water.

[0042] The groove 22Ag on the GDL21A side of the anode-side separator 22A functions as a passage for fuel gases such as hydrogen or hydrogen-containing gases. The groove 22Aw on the opposite side from the GDL21A side functions as a passage for cooling water.

[0043] The oxidizing gas flowing through groove 22Cg of the cathode-side separator 22C is supplied to the cathode 20C, and the fuel gas flowing through groove 22Ag of the anode-side separator 22A is supplied to the anode 20A, causing the above electrochemical reaction to occur. As a result, a DC voltage is generated between the cathode 20C and the anode 20A.

[0044] The material that makes up the separator 22 is not particularly limited, but examples include metallic materials such as stainless steel and carbon materials such as graphite. The PEFC20 is composed of the above-mentioned components.

[0045] Because PEFC20 can efficiently convert the chemical energy of hydrogen into electrical energy, widespread adoption of power generation systems utilizing PEFC20 is expected. Furthermore, because it is easier to miniaturize compared to conventional fuel cells, it is expected to be introduced as a small-scale fixed power source, such as in-vehicle power supplies and household power supplies.

[0046] The following describes methods for producing conductive titanium oxide, metal-supported conductive titanium oxide, MEA10, and PEFC20. [Method for producing conductive titanium oxide] A method for producing conductive titanium oxide includes a gelation step in which a solution containing a titanium source and a carbon source is gelled. It also includes a drying step in which the gel obtained in the gelation step is dried at a temperature of 105°C to 200°C to produce a dried body. Furthermore, it includes a heating step in which the dried body is heated at a temperature of 800°C to 1200°C in a hydrogen-containing atmosphere.

[0047] The titanium source is not particularly limited, and known titanium compounds can be used. Among the known titanium compounds, those that are easily soluble in solvents such as water are preferred. Specific examples of titanium compounds include titanium sulfate and titanium fluoride. Titanyl sulfate and titanium fluoride are relatively stable in the atmosphere, making them easy to handle.

[0048] The carbon source is not particularly limited, and known carbon-containing compounds can be used. Among known carbon-containing compounds, those that are easily soluble in solvents such as water are preferred. Furthermore, to function as a reducing agent for the titanium source, those with a relatively high carbon content are preferred. Examples of carbon-containing compounds with a relatively high carbon content include polymers in which carbon-carbon bonds form the main chain.

[0049] Specific examples of the above polymers include polyethylene glycol and polyvinyl alcohol. (Gelation process) In the gelation process, a solution containing a titanium source and a carbon source is first prepared using a solvent.

[0050] The solvent is not particularly limited, and any known solvent can be used. Examples of known solvents include water and alcohol. There are no particular restrictions on the type of water used; for example, distilled water, pure water, ultrapure water, purified water, tap water, etc., can be used.

[0051] There are no particular restrictions on the type of alcohol; for example, methanol, ethanol, propanol, etc., can be used. A mixture of water and alcohol in any proportion may also be used.

[0052] When preparing a solution containing a titanium source and a carbon source, it is preferable to add the titanium source and carbon source to the solvent and stir. Stirring can be done using a known stirrer. Alternatively, stirring may be done while heating. The heating temperature when stirring while heating is not particularly limited, but it is preferably between 30°C and 300°C.

[0053] The content of titanium source and carbon source in the above solution is not particularly limited, and the content can be selected as appropriate. The mass ratio of carbon source to titanium oxide (TiO2), assuming that all titanium source becomes titanium oxide (TiO2), is preferably 0.05 to 30, and more preferably 0.1 to 20.

[0054] Next, the solution containing the titanium source and the carbon source is gelled by stirring. Heating while stirring allows for faster and more uniform gelation. The heating temperature for gelation is not particularly limited, but it is preferably between 50°C and 300°C. Gelation may also be carried out without heating the solution. Alternatively, the solution may be heated but without stirring.

[0055] (drying process) In the drying process, the gel obtained in the gelation process is dried at a temperature of 105°C to 200°C to produce a dried product. The drying temperature is more preferably 110°C to 180°C, and even more preferably 110°C to 150°C.

[0056] Here, "dried material" refers to a material in which the solvent content is 20% by mass or less. The dried material can be rephrased as a precursor. By keeping the drying temperature within the above range, the gel can be dried efficiently. Furthermore, when using titanyl sulfate as the titanium source, raising the drying temperature to 105°C or higher allows for efficient removal of sulfur contained in the raw materials, thereby reducing the sulfur content of the dried product.

[0057] The drying time is not particularly limited, but is preferably between 0.5 hours and 40 hours, and more preferably between 3 hours and 30 hours. The drying process can be carried out using a known electric dryer.

[0058] After the drying process, a step of crushing the dried material into a powder may be performed as appropriate. The step of crushing the dried material can be rephrased as the step of grinding the dried material. (Heating process) In the heating step, the dried product obtained in the drying step is heated at a temperature of 800°C to 1200°C in a hydrogen-containing atmosphere. Preferably, the heating temperature is between 900°C and 1050°C.

[0059] By heating in a hydrogen-containing atmosphere at a heating temperature within the above numerical range, the titanium compounds contained in the dried material can be efficiently reduced with a carbon source to produce conductive titanium oxide. The above reduction reaction is also called a carbothermal reduction reaction.

[0060] The atmosphere containing hydrogen is not particularly limited and may be an atmosphere mixed with gases other than hydrogen. Examples of gases other than hydrogen include inert gases. Specific examples of inert gases include nitrogen gas, helium gas, and argon gas.

[0061] The heating time is not particularly limited, but it is preferably between 1 hour and 8 hours. By heating within the above numerical range, conductive titanium oxide can be obtained in a shorter time.

[0062] By following the above steps, conductive titanium oxide with an conductivity of 0.1 S / cm or higher, measured under a pressure of 10 MPa, can be produced. Furthermore, the above method for producing conductive titanium oxide allows for the efficient production of titanium oxide having a Magneli phase or a Ti3O5 composition as a single phase, with an average particle size of 500 nm or less. Specifically, conventional methods for producing titanium oxide having a Magneli phase or a Ti3O5 composition required strict control of the moisture content in the atmosphere and prolonged heating. As a result, it was difficult to produce a single phase, and there was a risk of particle size increasing due to prolonged heating. In contrast, the method for producing conductive titanium oxide of the present invention does not require strict control of the moisture content in the atmosphere, and production can be carried out in a shorter time. As a result, it is easy to produce a single phase, and the particle size can be made smaller. Production efficiency can also be improved.

[0063] Furthermore, after the heating process, a step may be taken to crush the calcined body obtained through the heating process into a powder. The step of crushing the calcined body can be rephrased as a step of grinding the calcined body.

[0064] [Method for manufacturing metal-supported conductive titanium oxide] The method for producing metal-supported conductive titanium oxide includes a dispersion step of dispersing the conductive titanium oxide produced by the above-mentioned method for producing conductive titanium oxide and a metal solution in an organic solvent having hydroxyl groups to prepare a dispersion. The method also includes a supporting step of heating the dispersion to support the metal contained in the metal solution onto the conductive titanium oxide.

[0065] (Dispersion process) In the dispersion step, the conductive titanium oxide produced by the above-described method for producing conductive titanium oxide and the metal solution are dispersed in an organic solvent containing hydroxyl groups to prepare a dispersion.

[0066] The type of metal dissolved in the metal solution is not particularly limited, and any metal used in electrode catalysts can be used. Furthermore, the solvent for the metal solution is not particularly limited; it may be water, an inorganic solvent such as an inorganic acid, or an organic solvent such as an alcohol.

[0067] The metals dissolved in the metal solution may be used individually or in combination of two or more types. The organic solvent having a hydroxyl group is not particularly limited. For example, an organic solvent having a hydroxyl group bonded to a hydrocarbon group can be used. The hydrocarbon group may be an aromatic hydrocarbon group or an aliphatic hydrocarbon group. The aliphatic hydrocarbon group may be a straight-chain aliphatic hydrocarbon group or a branched-chain aliphatic hydrocarbon group. It may be a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group.

[0068] Specific examples of organic solvents having a hydroxyl group include alcohols such as ethanol. Organic solvents containing hydroxyl groups may be used individually or in combination of two or more.

[0069] (Supporting process) In the loading process, the dispersion obtained in the dispersion process is heated to load the metal contained in the metal solution onto the conductive titanium oxide. Specifically, when the dispersion is heated, the metal in the metal solution is reduced by an organic solvent containing hydroxyl groups. The reduced metal particles precipitate on the surface of the conductive titanium oxide, thereby loading the metal onto the conductive titanium oxide.

[0070] The heating temperature is not particularly limited, but it is preferably between 20°C and 98°C, and more preferably between 25°C and 95°C. By keeping the heating temperature within the above numerical range, metal can be efficiently supported on conductive titanium oxide.

[0071] The heating time is not particularly limited, but it is preferably between 6 and 48 hours. By heating within this numerical range, the metal can be supported on the conductive titanium oxide in a shorter time. The support process can be carried out using a known electric furnace.

[0072] Furthermore, a post-processing step may be performed after the loading step. The post-processing steps are not particularly limited, but washing and drying steps may be performed. For example, the dispersion after the loading step may be filtered by suction and washed with distilled water. For example, the dispersion after the loading and washing steps may be air-dried, or it may be heated and dried in an inert gas atmosphere such as nitrogen gas. Both air drying and drying in an inert gas atmosphere may be performed.

[0073] For example, when drying by heating under an inert gas atmosphere, the conditions may include drying under a nitrogen gas atmosphere at a temperature of 20°C to 120°C for 6 to 48 hours, followed by further drying under a helium gas atmosphere at a temperature of 120°C to 400°C for 6 to 48 hours.

[0074] By going through the above steps, a metal-supported conductive titanium oxide can be obtained. In the metal-supported conductive titanium oxide, metal particles acting as a metal catalyst are dispersed and supported on the surface of the conductive titanium oxide. The supported metal particles are fine particles with an average particle diameter of approximately 1 nm to 5 nm. Because the average particle diameter of the metal particles is within the above numerical range, the catalytic activity can be improved when used as a catalyst layer.

[0075] [Method for manufacturing MEA] The method for producing MEA10 is not particularly limited. For example, a catalyst layer 12 may be formed on a known transfer substrate and bonded to the solid polymer electrolyte layer 11 by thermocompression bonding. Alternatively, a catalyst layer 12 may be formed on a pair of GDL21 and bonded to the solid polymer electrolyte layer 11 by thermocompression bonding. Furthermore, the catalyst layer 12 may be formed directly on the solid polymer electrolyte layer 11.

[0076] The method for forming the catalyst layer 12 is not particularly limited, but for example, it can be formed by applying a catalyst ink to a transfer substrate and drying it. The catalyst ink contains an electrode catalyst and a support. In addition to the above, the catalyst ink may also contain a polymer electrolyte and a solvent.

[0077] [PEFC manufacturing method] The method for manufacturing PEFC20 is not particularly limited. For example, a known adhesive is applied to the outer periphery of the solid polymer electrolyte layer 11 constituting the MEA10 that is not covered by a pair of catalyst layers 12. The gaskets 13 are then joined to the outer periphery of both sides of the solid polymer electrolyte layer 11 by placing a pair of gaskets 13 on top of this adhesive.

[0078] Furthermore, a pair of GDL21 are placed on top of the pair of catalyst layers 12 that make up the MEA10, and a pair of separators 22 are placed on top of the GDL21. PEFC20 can be manufactured by the above method. The manufacturing method for MEA10 and the manufacturing method for PEFC20 are not limited to the above method, and the order may be changed as appropriate.

[0079] The operation and effects of the conductive titanium oxide in this embodiment will be described. (1) Conductive titanium oxide has an electrical conductivity of 0.1 S / cm or higher when measured under a pressure of 10 MPa. Conductive titanium oxide has electrical conductivity comparable to graphite. Therefore, it can be used as a substitute for carbon materials commonly used as supports for catalyst layers. Because conductive titanium oxide has excellent durability, using it as a support for catalyst layers can effectively suppress the deterioration of the support's durability.

[0080] (2) The specific surface area of ​​conductive titanium oxide is 100 m² 2The specific surface area is greater than or equal to the above numerical range. Because the specific surface area is within this range, the amount of electrode catalyst supported can be relatively increased. Therefore, when used in the catalyst layer of a polymer electrolyte fuel cell, it can contribute to improving power generation performance.

[0081] (3) The metal-supported conductive titanium oxide comprises the conductive titanium oxide and metal particles supported on the conductive titanium oxide. Therefore, when used as a catalyst layer in a polymer electrolyte fuel cell, it can exhibit excellent power generation performance.

[0082] (4) A method for producing conductive titanium oxide comprises a gelling step of gelling a solution containing a titanium source and a carbon source, and a drying step of drying the gel obtained in the gelling step at a temperature of 105°C to 200°C to produce a dried body. It also comprises a heating step of heating the dried body at a temperature of 800°C to 1200°C in a hydrogen-containing atmosphere.

[0083] Therefore, conductive titanium oxides with an conductivity of 0.1 S / cm or higher, measured under a pressure of 10 MPa, can be produced. Furthermore, titanium oxides having a Magnelli phase or a Ti3O5 composition as a single phase and an average particle size of 500 nm or less can be efficiently manufactured.

[0084] (5) The method for producing metal-supported conductive titanium oxide includes a dispersion step of dispersing the conductive titanium oxide produced by the above-mentioned method for producing conductive titanium oxide and a metal solution in an organic solvent having hydroxyl groups to prepare a dispersion. The method also includes a supporting step of heating the dispersion to support the metal contained in the metal solution onto the conductive titanium oxide.

[0085] Therefore, since metal particles, which are fine particles with an average particle diameter of approximately 1 nm to 5 nm, can be supported on conductive titanium oxide, catalytic activity can be improved when used as a catalyst layer.

[0086] [Example of changes] This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0087] The conductive titanium oxide and metal-supported conductive titanium oxide of the present invention are not limited to their use in membrane electrode assemblies of polymer electrolyte fuel cells. They may also be used as membrane electrode assemblies in fuel cells other than polymer electrolyte fuel cells. Furthermore, they may be used as a support for a catalyst layer or as a catalyst layer other than a membrane electrode assembly.

[0088] In this embodiment, one of the pair of catalyst layers 12 constitutes the anode-side electrode catalyst layer 12A and the other constitutes the cathode-side electrode catalyst layer 12C, but the embodiment is not limited to this. One of the pair of catalyst layers 12 may constitute the cathode-side electrode catalyst layer 12C and the other constitutes the anode-side electrode catalyst layer 12A. The same applies to the pair of gaskets 13, the pair of GDLs 21 and the pair of separators 22. In other words, the polymer electrolyte fuel cell 20 may have a structure inverted from the one shown in Figure 1. [Examples]

[0089] The following are examples to illustrate the structure and effects of the present invention in more detail, but the present invention is not limited to these examples. [Fabrication of conductive titanium oxide] (Example 1) Titanyl sulfate, with the chemical formula TiOSO4·nH2O, was used as the titanium source.

[0090] Polyethylene glycol 400 (hereinafter also simply referred to as "polyethylene glycol"), which has an average molecular weight of 360 to 440, was used as the carbon source. A mixed solution was prepared by mixing 491 mL of distilled water with 9 mL of polyethylene glycol. 24.5 g of titanyl sulfate was added to this mixed solution. This mixed solution was stirred for 15 hours while being heated to 80°C using a known stirrer to induce gelation.

[0091] The resulting gel was dried at 150°C for 6 hours using a known electric dryer. The resulting dried material was ground into a powder using an agate mortar. Next, 1 g of the powdered dry material was placed on a known alumina boat. This alumina boat was set in a quartz tubular furnace, and both ends of the quartz tubular furnace were sealed. Nitrogen gas was introduced into the quartz tubular furnace for 20 minutes to replace the inside of the furnace with nitrogen gas.

[0092] Subsequently, the gas circulating within the quartz tubular furnace was switched to a mixture of argon and hydrogen gas. The proportion of hydrogen gas in the mixture was 10% by volume. The quartz tubular furnace was heated to 967°C at a heating rate of 10°C / min to calcine the dried material. After holding it at 967°C for 3 hours, it was allowed to cool naturally to room temperature. Hereafter, the temperature at which the dried material is heated will also be referred to as the calcination temperature.

[0093] The dried material was calcined to obtain the calcined material, which was then ground in an agate mortar to obtain the conductive titanium oxide of Example 1. (Example 2) Conductive titanium oxide was obtained in the same manner as in Example 1, except that the amount of dried powder placed on the alumina boat was changed to 2 g.

[0094] (Example 3) Conductive titanium oxide was obtained in the same manner as in Example 1, except that the amount of dried powder placed on the alumina boat was changed to 4 g.

[0095] (Example 4) Conductive titanium oxide was obtained in the same manner as in Example 1, except that the firing temperature was changed to 1000°C.

[0096] (Example 5) Conductive titanium oxide was obtained by the same method as in Example 1, except that titanyl sulfate was replaced with titanium fluoride, which has the chemical formula TiF4.

[0097] (Comparative Example 1) Conductive titanium oxide was obtained by the same method as in Example 1, except that 0.4 g of titanium oxide with the chemical formula TiO2 was used as the powdered dried material, and the firing temperature was changed to 1050°C and held for 6 hours.

[0098] (Comparative Example 2) Conductive titanium oxide was obtained in the same manner as in Example 1, except that the drying temperature of the gel was changed to 100°C. The obtained conductive titanium oxide had a strong sulfurous odor derived from the raw materials and was difficult to handle, so no further evaluation was performed.

[0099] [Evaluation Method] (XRD measurement) The X-ray diffraction patterns of conductive titanium oxides from Examples 1-5 and Comparative Example 1 were measured using an XRD diffractometer (MiniFlex600, manufactured by Rigaku Corporation). The results are shown in Figures 2-4.

[0100] (Measurement of powder conductivity) The conductivity of conductive titanium oxides in Example 1 and Comparative Example 1 was measured using an automated powder resistance measurement system (MCP-PD600, manufactured by Nitto Seikou Analytech Co., Ltd.). For reference, the conductivity of commercially available carbon black was also measured. The conductivity was measured while applying pressure in the range of 3 MPa to 64 MPa. The results are shown in Figure 5.

[0101] (Pore distribution measurement) The adsorption isotherm of the conductive titanium oxide from Example 1 was measured at -196°C using a specific surface area and pore size distribution analyzer (BELSORP MINI X, manufactured by Microtrac-Bel, Inc.). Nitrogen (N2) was used as the adsorbed molecule. The results are shown in Figure 6.

[0102] (Measurement of average particle size) Conductive titanium oxides of Examples 1-5 and Comparative Example 1 were observed using a known scanning electron microscope. In each example, the particle size of 10 randomly selected conductive titanium oxides was measured, and the average value was taken as the average particle size.

[0103] [Fabrication of metal-supported conductive titanium oxide] (Example 6) 0.80 g of conductive titanium oxide (Ti4O7) prepared by the method described in Example 1 was weighed out. This was dispersed in 100 mL of distilled water and ultrasonically stirred at 28 kHz for 5 minutes.

[0104] Next, 4.39 g of a dinitrodiamine platinum nitric acid solution containing 4.555% by mass of platinum was added to 100 mL of distilled water and sonicated at 28 kHz for 5 minutes. These were mixed so that the mass ratio of conductive titanium oxide to platinum (platinum:conductive titanium oxide) was 1:19.

[0105] The resulting mixed solution was placed in a container fitted with a reflux condenser. The reflux condenser was then immersed in a 25°C oil bath. The mixture was stirred using a magnetic stirrer at 800 rpm for 1 hour at room temperature. Ethanol was added to this container in three separate additions of 10 mL each. The mixture was then stirred at 800 rpm for 30 minutes at room temperature.

[0106] Subsequently, the oil bath temperature was increased to 95°C. In this state, the mixture was stirred at a rotation speed of 600 rpm for 12 hours to support platinum particles on the conductive titanium oxide. The resulting dispersion was filtered by suction and washed with 1000 mL of distilled water.

[0107] The obtained powder was air-dried overnight at room temperature. Then, using a ceramic electric tubular furnace and a simple temperature control unit, it was heated at 80°C for 10 hours under a nitrogen gas atmosphere (60 cm³). 3 It was dried at 60cm² ( / min). Then, the atmosphere was changed to helium gas (60cm²). 3 The mixture was then dried at 300°C for 2 hours using the following procedure. A metal-supported conductive titanium oxide was obtained using this method. The amount of platinum supported on the conductive titanium oxide was 5% by mass.

[0108] (Example 7) In Example 6, the metal-supported conductive titanium oxide of Example 7 was obtained by the same method as in Example 6, except that the mass ratio of conductive titanium oxide to platinum (platinum:conductive titanium oxide) was 1:9. The amount of platinum supported on the conductive titanium oxide was 10% by mass.

[0109] (Example 8) In Example 6, the metal-supported conductive titanium oxide of Example 8 was obtained by the same method as in Example 6, except that the mass ratio of conductive titanium oxide to platinum (platinum:conductive titanium oxide) was 2:8. The amount of platinum supported on the conductive titanium oxide was 20% by mass.

[0110] (Example 9) In Example 6, the metal-supported conductive titanium oxide of Example 9 was obtained by the same method as in Example 6, except that the mass ratio of conductive titanium oxide to platinum (platinum:conductive titanium oxide) was 3:7. The amount of platinum supported on the conductive titanium oxide was 30% by mass.

[0111] (Comparative Example 3) In Example 8, the metal-supported conductive titanium oxide of Comparative Example 3 was obtained by the same method as in Example 8, except that the titanium oxide of Comparative Example 1 was used instead of the conductive titanium oxide of Example 1. The amount of platinum supported on the conductive titanium oxide was 20% by mass.

[0112] [MEA preparation] (Example 10) A metal-supported conductive titanium oxide with a platinum load of 5% by mass, prepared in Example 6, was used as the cathode catalyst, and a commercially available Pt / C (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was used as the anode catalyst to prepare an MEA, which was then incorporated into a single cell.

[0113] First, carbon paper was prepared to serve as the support for the electrode catalyst layer. After forming the electrode catalyst layer on the carbon paper, it was thermocompressed onto the polymer electrolyte membrane. 0.36 g of carbon black (Vulcan XC-72R, manufactured by Lion Corporation) was added to 7.2 mL of ethanol and ultrasonically stirred at 28 kHz for 10 minutes at room temperature.

[0114] 2.2 g of a polytetrafluoroethylene (hereinafter also referred to as "PTFE") solution diluted to 10.9% by mass was weighed and added to the mixed solution. Next, the mixture was stirred at room temperature for 20 minutes using a glass rod to prevent the PTFE from agglomerating.

[0115] After adding a small amount of ethanol using a dropper bottle, the prepared carbon black ink was applied to carbon paper and fired at 350°C for 1 hour in an air atmosphere. A Nafion solution containing 5% by mass of platinum-supported metal-supported conductive titanium oxide was mixed so that the mass ratio of metal-supported conductive titanium oxide to Nafion after drying (Nafion:metal-supported conductive titanium oxide) was 1:9, and the mixture was applied to carbon paper.

[0116] Similarly, Pt / C was applied to the carbon paper for the anode. The carbon paper for the cathode had a platinum content of 0.5 mg / cm² per geometric area. 2 The carbon paper for the anode contains 0.2 mg / cm³ 2 Adjust the amount of coating applied so that the electrode area is 2.2 × 2.2 cm². 2 That's what I decided.

[0117] Carbon paper for the anode and cathode is placed on both sides of the Nafion film, and a Teflon sheet frame (4.0 x 4.0 cm) is placed on top of it. 2 It was covered with aluminum foil (0.1 mm thick). Note that Teflon is a registered trademark.

[0118] The inside of the Teflon sheet frame was cut out to a size of 2.3 cm x 2.3 cm. The sheet was heat-sealed at 135°C for 20 minutes under a pressure of 10.0 MPa, and the Teflon sheet was removed to obtain the MEA (Metal-Efficient Analysis).

[0119] Pure hydrogen and pure oxygen were supplied to the anode and cathode at a flow rate of 85 ml / min, respectively, to generate electricity. The hydrogen was humidified to 100% at 80°C and the oxygen to 100% at 75°C, and the current density-voltage characteristics were obtained by setting the single cell to 80°C.

[0120] (Example 11) In Example 10, the cathode catalyst was changed to a metal-supported conductive titanium oxide with a platinum load of 10% by mass, which was synthesized in Example 7. Except for this change, an MEA and a single cell were fabricated using the method described in Example 10, and power generation characteristics were obtained.

[0121] (Example 12) In Example 10, the cathode catalyst was changed to a metal-supported conductive titanium oxide with a platinum load of 20% by mass, which was synthesized in Example 8. Except for this change, an MEA and a single cell were fabricated using the method described in Example 10, and power generation characteristics were obtained.

[0122] (Example 13) In Example 10, the cathode catalyst was changed to a metal-supported conductive titanium oxide with a platinum load of 30% by mass, which was synthesized in Example 9. Except for this change, an MEA and a single cell were fabricated using the method described in Example 10, and power generation characteristics were obtained.

[0123] (Example 14) In Example 12, the MEA and single cell were fabricated and power generation characteristics were obtained using the method described in Example 10, except that the anode catalyst was changed to a metal-supported conductive titanium oxide with a platinum load of 20 mass%, which was synthesized in Example 8. Specifically, in the MEA of Example 14, a metal-supported conductive titanium oxide with a platinum load of 20 mass% was used for both the anode and cathode electrodes.

[0124] (Reference example 1) In Example 10, the MEA and single cell were fabricated and power generation characteristics were obtained using the method described in Example 10, except that the cathode catalyst was changed to Pt / C, the same as the anode catalyst. That is, the MEA in Reference Example 1 used Pt / C for both the anode and cathode electrodes.

[0125] (Comparative Example 4) In Example 14, an MEA and a single cell were fabricated and power generation characteristics were obtained using the method described in Example 14, except that the metal-supported conductive titanium oxide with a platinum load of 20% by mass, synthesized in Comparative Example 3, was used as the catalyst for both electrodes.

[0126] [Evaluation Method] (Single-cell power generation characteristics) The power generation characteristics of single cells fabricated using the MEAs of Examples 10-14, Reference Example 1, and Comparative Example 4 were measured. The results are shown in Figures 7 and 8.

[0127] (Accelerated degradation test) Using the MEA from Example 14, an accelerated degradation test was performed to evaluate its durability. After obtaining the initial power generation characteristics, the voltage was maintained at 0.6V for 30 seconds while supplying hydrogen to the anode and oxygen to the cathode.

[0128] The square wave voltage was then held at 1.0V for 3 seconds, followed immediately by a 3-second hold at 0.6V, and this cycle was repeated 10,000 times. The power generation characteristics were acquired every 1,000 cycles. The results are shown in Figure 9.

[0129] [Evaluation Results] From the X-ray diffraction patterns shown in Figures 2-4, it was confirmed that the conductive titanium oxides in Examples 1-3 were single-phase Ti4O7. Furthermore, it was confirmed that the conductive titanium oxide in Example 4 was single-phase Ti3O5. Finally, it was confirmed that the conductive titanium oxide in Example 5 was single-phase Ti2O3.

[0130] As shown in Figure 5, the results of the powder conductivity measurement revealed that commercially available carbon black had a conductivity of approximately 10 S / cm at a pressure of 10 MPa. In contrast, the conductive titanium oxide of Comparative Example 1 had a conductivity of approximately 0.001 S / cm at a pressure of 10 MPa. The conductive titanium oxide of Example 1 was confirmed to have a conductivity of approximately 1 S / cm at a pressure of 10 MPa. Furthermore, high conductivity was confirmed across the entire measurement range from 3 MPa to 64 MPa.

[0131] From the adsorption / desorption isotherms shown in Figure 6, a hysteresis phenomenon was observed in the conductive titanium oxide of Example 1, where the adsorption isotherm and desorption isotherm did not coincide, suggesting that the sample was a porous material. This is presumed to be due to the aggregation of multiple conductive titanium oxide particles. The specific surface area calculated by the Brunauer-Emmett-Teller method was 172 m². 2 The value was found to be / g, confirming that its specific surface area is an order of magnitude larger than that of typical titanium oxides.

[0132] Observations using a scanning electron microscope revealed that the average particle sizes of the conductive titanium oxides in Examples 1-5 were 0.1 μm, 0.1 μm, 0.1 μm, 0.2 μm, and 0.3 μm, respectively. The average particle size of the conductive titanium oxide in Comparative Example 1 was 3 μm. Based on these average particle sizes, it is presumed that the conductive titanium oxides in Examples 2-5 have a specific surface area similar to that of Example 1.

[0133] As shown in Figures 7 and 8, the power generation characteristics of Comparative Example 4 were found to be poor because it used a titanate compound with low conductivity. In contrast, improvements in power generation characteristics were confirmed in all of Examples 10 to 14.

[0134] In Examples 10-13, it was confirmed that increasing the platinum load to 20%-30% by mass improved the power generation characteristics. This is presumed to be due to the large specific surface area of ​​Ti4O7, which provides sufficient surface area for supporting platinum. Generally, the performance of a PEFC is determined by the cathode, but it was found that the metal-supported conductive titanium oxide provided by the present invention functions sufficiently as a cathode catalyst.

[0135] In Example 14, Ti4O7 with platinum supported on both electrodes was used, but it demonstrated power generation performance equivalent to that of Example 12, where platinum was used only on the cathode side, and Reference Example 1, where Pt / C was used on both electrodes. It was found that platinum-supported Ti4O7 also functions well as an anode catalyst.

[0136] Figure 9 shows the power generation characteristics of a single cell before and after conducting 10,000 accelerated degradation tests. As shown in Figure 9, in the test using the MEA of Example 14, the performance did not deteriorate even after 10,000 accelerated degradation tests, confirming its high durability. This indicates that using the conductive titanium oxide of the present invention as a support for the catalyst layer can suppress the deterioration of the support's durability. [Explanation of Symbols]

[0137] 10 Membrane electrode assembly 11 Solid polymer electrolyte layer 12 Catalyst layer 12A Anode side electrode catalyst layer 12C cathode side electrode catalyst layer 13 Gasket 13A Anode side gasket 13C Cathode side gasket 20 Polymer electrolyte fuel cell 20A Anode 20C Cathode 21 Gas diffusion layer 21A Anode-side gas diffusion layer 21C Cathode-side gas diffusion layer 22 Separators 22A Anode-side separator 22C Cathode-side separator

Claims

1. A gelling step in which a solution containing titanium sulfate or titanium fluoride as a titanium source and polyethylene glycol as a carbon source is gelled, A drying step is performed to produce a dried body by drying the gel obtained in the gelation step at a temperature of 105°C to 200°C, A method for producing conductive titanium oxide, characterized by comprising a heating step of heating the dried body at a temperature of 800°C to 1200°C in a hydrogen-containing atmosphere.

2. A dispersion step of dispersing conductive titanium oxide produced by the method for producing conductive titanium oxide described in claim 1 and a metal solution in an organic solvent having hydroxyl groups to prepare a dispersion, A method for producing a metal-supported conductive titanium oxide, characterized by comprising a supporting step of heating the dispersion to support the metal contained in the metal solution onto the conductive titanium oxide.

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