Method for manufacturing electrode materials

Abstract

To provide a manufacturing method of an electrode material capable of fixing an electron conductive oxide on a pore outer surface and a pore inner surface of mesoporous carbon.SOLUTION: A manufacturing method of an electrode material includes following steps (1) to (4). Step (1): MC is brought into contact with anhydrous alcohol and a fluid dispersion containing MC, in which the anhydrous alcohol is led into pores is obtained. Step (2): A solvent is removed from a mixed solution obtained by mixing the liquid dispersion containing MC in which the anhydrous alcohol is led in, tin alkoxide solution of the electronic conductive oxide and water / alcohol solvent, and a dried product in which a hydrolysate of tin alkoxide is fixed to MC is obtained. Step (3): Heat treatment is performed on the obtained dried product, thereby obtaining a porous composite carrier in which the electron conductive oxide is fixed on a pore inner surface and a pore outer surface of MC. Step (4): Heat treatment is performed under an inactive gas atmosphere upon the dried product obtained by removing the solvent after mixing the obtained porous composite carrier with a solution containing an electrode catalyst precursor until becoming uniform.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing electrode materials suitable for electrodes used in fuel cells. [Background technology]

[0002] Polymer electrolyte fuel cells (PEFCs) are already commercially available in fuel cell vehicles (FCVs) that use them as a power source, and their applications are expected to expand to trucks, buses, ships, and other vehicles in the future. Generally, a PEFC has a structure in which a membrane electrode assembly (MEA), which has a pair of electrodes placed on both sides of a solid polymer electrolyte membrane, is sandwiched between separators in which gas channels are formed. Fuel cell electrodes (especially PEFC electrodes) generally consist of an electrode catalyst layer made of an electrode material with electrode catalytic activity and a polymer electrolyte, and a gas diffusion layer that combines gas permeability and electronic conductivity.

[0003] Currently, electrode materials widely used for PEFCs consist of electrode catalyst nanoparticles (typically Pt or Pt alloy nanoparticles) dispersed and supported on a carbon-based support.

[0004] On the other hand, since the electrolyte membrane of a PEFC is acidic (pH=0~3), the electrode material of a PEFC is used in an acidic atmosphere. Also, while the cell voltage during normal operation is 0.4~1.0V, it is known that the cell voltage can rise to 1.5V during startup and shutdown. Under these operating conditions of a PEFC, the cathode and anode are in a region where the carbon-based material that serves as the support decomposes into carbon dioxide (CO2). Therefore, in the cathode, a reaction occurs in which the carbon support is electrochemically oxidized and decomposed into CO2, resulting in corrosion of the carbon support (carbon corrosion), which causes aggregation and detachment of Pt particles, the catalytic active component, and becomes a factor in the deterioration of fuel cell performance. Furthermore, not only in the cathode but also in the anode, if there is a shortage of fuel gas during the initial stages of operation, a voltage drop or concentration polarization occurs in that area, resulting in a localized potential opposite to the normal potential, which can cause the electrochemical oxidative decomposition reaction of carbon.

[0005] To address the aforementioned problem of carbon carrier corrosion, electrode materials using thermodynamically stable electronically conductive oxides (such as SnO2 and TiO2) under PEFC operating conditions (strong acidity, high potential) have been reported (Patent Documents 1 and 2). Such electrode materials offer excellent durability derived from metal oxides.

[0006] In recent years, electrode materials have attracted attention in which mesoporous carbon is used as the framework for the catalyst support, and Pt fine particles are supported within the pores (mesopores) of the mesoporous carbon (for example, Patent Documents 3 and 4). Mesoporous carbon has excellent conductivity, facilitates gas diffusion, and has a high surface area, so when it is used as a support for the electrode catalyst of a polymer electrolyte fuel cell, an electrode with excellent power generation performance can be obtained.

[0007] The methods for supporting (fixing) electronically conductive oxides described in Patent Documents 1 and 2 involve adding ammonia water or pure water dropwise to a precursor dissolved in an organic solvent to obtain the electronically conductive oxide. However, these methods have a fast reaction rate that is difficult to control, resulting in a large primary particle size of the generated electronically conductive oxide (10 nm or more), and the primary particles are supported (fixed) to the carbon support in an aggregated state. Therefore, it was considered extremely difficult to uniformly support (fix) the electronically conductive oxide within the mesopores of mesoporous carbon, even when attempting to apply these methods to mesoporous carbon.

[0008] On the other hand, the present inventors have reported in Patent Document 5 a method for manufacturing an electrode material for a fuel cell, which includes the steps of mixing mesoporous carbon and an alkoxide compound of an electron-conductive oxide precursor in a non-aqueous organic solvent until homogeneous, then removing the solvent and drying the resulting dried product, decomposing the electron-conductive oxide precursor by hydrolysis with water vapor, and then heat-treating the dried product to fix the electron-conductive oxide to the surface of the mesoporous carbon. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent No. 5322110 [Patent Document 2] Japanese Patent No. 6598159 [Patent Document 3] Japanese Patent No. 6969996 [Patent Document 4] Japanese Patent No. 6931808 [Patent Document 5] Japanese Patent Application No. 2022-141541 [Summary of the Invention] [Problems to be Solved by the Invention]

[0010] In the method of introducing an electronically conductive oxide precursor into the pores of mesoporous carbon and then introducing water vapor for hydrolysis disclosed in Patent Document 5, although an electronically conductive oxide can be reliably formed inside the pores of mesoporous carbon, there is room for improvement in terms of productivity.

[0011] Under such circumstances, an object of the present invention is to provide a method for manufacturing an electrode material that can fix an electronically conductive oxide on the outer surface and inner surface of the pores of mesoporous carbon without performing hydrolysis with water vapor, and has excellent durability against carbon corrosion and excellent electronic conductivity due to mesoporous carbon. [Means for Solving the Problems]

[0012] As a result of intensive research to solve the above problems, the present inventor has found that the following invention meets the above object, and has arrived at the present invention.

[0013] That is, the present invention relates to the following invention. <1> A method for producing an electrode material comprising a porous composite carrier made of mesoporous carbon and an electronically conductive oxide mainly composed of tin oxide fixed to the inner and outer surfaces of the pores of the mesoporous carbon, and electrode catalyst particles supported on the porous composite carrier, the method comprising the following steps (1) to (4). Step (1): A step of contacting mesoporous carbon with anhydrous alcohol to obtain a dispersion containing mesoporous carbon in which anhydrous alcohol has been introduced into the pores. Step (2): A mixture is obtained by mixing the dispersion containing mesoporous carbon into which anhydrous alcohol obtained in Step (1), the tin alkoxide solution containing the electronically conductive oxide tin alkoxide, and a water / alcohol solvent to obtain a mixed solution. The solvent is then removed from the mixed solution by distillation to obtain a dried product in which hydrolysates of the tin alkoxide are fixed to the inner and outer surfaces of the pores of the mesoporous carbon. Step (3): A step in which the dried material obtained in step (2) is heat-treated to obtain a porous composite carrier in which an electron-conducting oxide is fixed to the inner surface and outer surface of the pores of the mesoporous carbon. Step (4): A process in which the porous composite support obtained in step (3) and the solution containing the electrode catalyst precursor are mixed until homogeneous, and the solvent is removed by distillation, and the resulting dry product is heat-treated in an inert gas atmosphere. <2> In step (1), the anhydrous alcohol is one or more selected from methanol, ethanol, n-propanol, and isopropanol. <1> A method for manufacturing the electrode material described above. <3> In step (2), after obtaining a dried product in which hydrolyzed tin alkoxide is fixed to the inner and outer pore surfaces of the mesoporous carbon, the obtained dried product is dispersed in a niobalkoxide solution, and the solvent is removed by distillation to obtain a dried product. <1> or <2> A method for manufacturing the electrode material described above. <4> In step (2), the proportion of water in the mixed solution, out of a total of 100% by volume of water and alcohol (including the anhydrous alcohol in the dispersion), is 0.1% by volume or more and 10% by volume or less. <1> from <3> A method for manufacturing an electrode material as described in any of the following. <5> In step (3), the heat treatment temperature is between 350°C and 650°C. <1> from <4> A method for manufacturing an electrode material as described in any of the following. <6> In step (4), the electrode catalyst precursor is a noble metal acetylacetonate. <1> from <5> A method for manufacturing an electrode material as described in any of the following. [Effects of the Invention]

[0014] The present invention provides a method for manufacturing an electrode material that possesses both excellent resistance to carbon corrosion and excellent electronic conductivity due to mesoporous carbon. [Brief explanation of the drawing]

[0015] [Figure 1] (a) is a conceptual schematic diagram of the electrode material according to the present invention, (b) is a magnified schematic diagram of the vicinity of the pore (electronically conductive oxide dispersed and fixed), and (c) is a magnified schematic diagram of the vicinity of the pore (electronically conductive oxide continuously fixed (coating)). [Figure 2] This is a flowchart showing the procedure for preparing the electrode material (without electrode catalyst) used in the experimental example. [Figure 3] This is the XRD profile of the electrode material (without electrode catalyst) used in the experimental example. [Figure 4] The images show the microstructure observation results of the electrode material (electrode catalyst unsupported, 600°C) in experimental example A3, with (a) an SEM image and (b) a TEM image. [Figure 5] This is the microstructure observation result (SEM image) of the electrode material (electrode catalyst unsupported, 700°C) for experimental example A4. [Figure 6] This is a limited-field electron beam diffraction analysis of the electrode material (without electrode catalyst support, at 400°C, 500°C, and 600°C) as an example of an experimental study. [Figure 7] These are STEM / EDS mapping images of electrode materials (electrode catalyst unsupported, SnO2 adhesion rate 20-75 wt%) from experimental examples A3, A5-A7. [Figure 8] The images on the right (a) to (c) show STEM images of the electrode material (electrode catalyst unsupported, SnO2 adhesion rate 40 wt%) for experimental example A6, and the left figure shows a schematic diagram of the arrangement of tin oxide particles inside the mesopore. [Figure 9] This is a flowchart of the procedure for electrode catalyst loading using the acetylacetonate method. [Figure 10] This is a STEM / EDS analysis of the electrode material (Pt / Sn0.98Nb0.02O2 / MC) for experimental example A3. [Figure 11] This diagram shows the conditions for the start-up / shutdown cycle test. [Figure 12] This figure shows the change in electrochemical effective surface area (ECSA) of the electrode material of the example (SnO2 adhesion rate 20-75 wt%) and the electrode material of the comparative example (SnO2 adhesion rate 0 wt%) during a start-stop cycle test. [Modes for carrying out the invention]

[0016] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples, and can be modified and implemented as such without departing from the spirit of the invention. In this specification, "~" is used to mean an expression that includes the numerical value or physical quantity before and after it.

[0017] The present invention relates to a method for producing an electrode material comprising mesoporous carbon and an electronically conductive oxide mainly composed of tin oxide fixed to the inner and outer surfaces of the pores of the mesoporous carbon, and electrode catalyst particles supported on the porous composite carrier, the method comprising the following steps (1) to (4) (hereinafter referred to as "the method for producing the electrode material of the present invention" or simply "the method for producing the present invention").

[0018] Step (1): A step of contacting mesoporous carbon with anhydrous alcohol to obtain a dispersion containing mesoporous carbon in which anhydrous alcohol has been introduced into the pores. Step (2): A mixture is obtained by mixing the dispersion containing mesoporous carbon into which anhydrous alcohol obtained in Step (1), the tin alkoxide solution containing the electronically conductive oxide tin alkoxide, and a water / alcohol solvent to obtain a mixed solution. The solvent is then removed from the mixed solution by distillation to obtain a dried product in which hydrolysates of the tin alkoxide are fixed to the inner and outer surfaces of the pores of the mesoporous carbon. Step (3): A step in which the dried material obtained in step (2) is heat-treated to obtain a porous composite carrier in which an electron-conducting oxide is fixed to the inner surface and outer surface of the pores of the mesoporous carbon. Step (4): A process in which the porous composite support obtained in step (3) and the solution containing the electrode catalyst precursor are mixed until homogeneous, and the solvent is removed by distillation, and the resulting dry product is heat-treated in an inert gas atmosphere.

[0019] In the electrode material manufactured by the manufacturing method of the present invention (hereinafter sometimes referred to as "the electrode material of the present invention"), an electronically conductive oxide mainly composed of tin oxide is fixed to part or all of the inner surface and outer surface of the pores of the mesoporous carbon, and the electrode catalyst particles have a structure in which they are supported on the electronically conductive oxide. That is, the electrode catalyst particles are supported on the mesoporous carbon via the electronically conductive oxide.

[0020] In the following, tin alkoxides (and other alkoxides containing doping elements) that serve as raw materials for electron-conducting oxides mainly composed of tin oxide may be referred to as "raw material alkoxides."

[0021] Furthermore, in this specification, "fixed" means that the hydrolyzed alkoxide (electronically conductive oxide precursor) or electronically conductive oxide is fixed to the inner and outer pore surfaces of the mesoporous carbon, which is the carrier skeleton, to the extent that it does not easily detach (peel off).

[0022] As will be described in detail later, one of the features of the method for manufacturing electrode materials of the present invention is that anhydrous alcohol is introduced into the pores of mesoporous carbon in step (1). Mesoporous carbon is porous carbon having pores in the mesopore region (2-50 nm). When fixing hydrolysates (electronically conductive oxide precursors) of raw material alkoxides to the surface of mesoporous carbon, it is difficult to introduce the raw material alkoxide, which is a precursor compound of the electronically conductive oxide, and water for the hydrolysis of the raw material alkoxide into the pores of untreated mesoporous carbon. As a result, in untreated mesoporous carbon, most of the hydrolysates of the raw material alkoxide are fixed to the outer surface of the pores. To address this challenge, the manufacturing method of the present invention introduces anhydrous alcohol, an amphiphilic solvent, into the pores of mesoporous carbon. This facilitates the introduction of the raw material alkoxide and water / alcohol solvent into the pores of the mesoporous carbon in step (2). When the solvent is distilled off in this state, the alcohol component is preferentially removed, resulting in a relatively high concentration of water. This allows the hydrolysis reaction of the raw material alkoxide to proceed, and the hydrolyzed product of the raw material alkoxide (electronically conductive oxide precursor) can be fixed not only to the outer surface of the pores of the mesoporous carbon but also to the inner surface of the pores. Therefore, by heat-treating the dried material obtained in step (2), a porous composite support can be obtained in which the electronically conductive oxide is fixed to the inner and outer surfaces of the pores of the mesoporous carbon (step (3)). After mixing the obtained porous composite support and a solution containing the electrode catalyst precursor until homogeneous, the solvent is distilled off, and the resulting dried material is heat-treated in an inert gas atmosphere to obtain the desired electrode material in which electrode catalyst particles are supported on the porous composite support (step (4)).

[0023] Preferred embodiments of the present invention will be described in detail below with reference to the drawings.

[0024] Figure 1(a) is a schematic diagram showing a typical configuration of the electrode material of the present invention, and Figure 1(b) is an enlarged schematic diagram of the vicinity of the pore.

[0025] As shown in Figure 1(a), the electrode material 1 according to the present invention is composed of a porous composite carrier consisting of a mesoporous carbon 2 which is a carrier skeleton and particulate electronically conductive oxide 3a fixed to the mesoporous carbon 2 (inner surface 2a and outer surface 2b of the pores), and electrode catalyst particles 3b supported on the electronically conductive oxide 3a.

[0026] The mesoporous carbon 2 (hereinafter sometimes referred to as "the mesoporous carbon according to the present invention"), which is the support skeleton of the electrode material 1, is a porous carbon having a large number of pores in the mesopore region.

[0027] In this specification, "pore" refers to pores with a diameter of 150 nm or less (especially pores with a diameter of 100 nm or less). "Mesopore region pores" refers to pores with a diameter of 2 nm to 50 nm. Furthermore, in this specification, "micropore region pores" refers to pores with a diameter of less than 2 nm, and "macropore region pores" refers to pores with a diameter greater than 50 nm and less than or equal to 150 nm.

[0028] As mesoporous carbon 2, porous carbon having pores in the mesopore region (2-50 nm) can be used, but preferably the pore diameter is 3 nm to 40 nm. Within this range, even when electron-conducting oxides or electrode catalysts are fixed (supported) on the inner wall of the pores, the diffusion of substances into the pores is not significantly hindered and proceeds smoothly.

[0029] Furthermore, when manufacturing electrodes for fuel cells using the electrode material of the present invention, the electrode material of the present invention is mixed with a proton-conducting electrolyte material (ionomer). However, since the proton-conducting electrolyte material (ionomer) is several tens of nanometers in size, it cannot penetrate into the mesopores, which have a small pore diameter. Therefore, it is possible to suppress ionomer-derived poisoning of the electrode catalyst metal supported in the pores of mesoporous carbon via the aforementioned electron-conducting oxide.

[0030] The mesoporous carbon according to the present invention may contain regions other than pores in the mesopore region (2 nm to 50 nm), such as micropore regions and macropores, but it is preferable that the proportion of pores in the mesopore region is high.

[0031] The pore structure (pore size, shape, etc.) of mesoporous carbon can be confirmed by observation with an electron microscope. Examples of electron microscopes include field emission scanning electron microscopes (FESEM) and scanning transmission electron microscopes (STEM).

[0032] In mesoporous carbon 2, the pores in the mesoporous regions preferably have a three-dimensional network structure, with some or all of the pores in a mesoporous region communicating with pores in adjacent mesoporous regions, in addition to individual pores independent of other pores. The presence of these communicating pores promotes the diffusion of substances within the pores of the mesoporous carbon.

[0033] The size and shape of the electrode material depend on the size and shape of the mesoporous carbon that forms its framework. The size and shape of the mesoporous carbon are determined within a range that allows the electrode material to be in continuous contact when forming a fuel cell electrode, and that creates a space sufficient for the smooth diffusion of gases such as hydrogen and oxygen, and the discharge of water (steam) within the fuel cell electrode.

[0034] The mesoporous carbon used in the electrode material of the present invention may be synthesized as appropriate or a commercially available product may be used. Examples of commercially available products include the CNovel series (designed mesopore size: 5~150nm) manufactured by Toyo Tanso Co., Ltd., which is a mesoporous carbon with MgO as a template.

[0035] (Electronically conductive oxides) As shown in Figure 1, in the electrode material 1 of this embodiment, the electronically conductive oxide 3a is fixed to the inner surface 2a of the pores in the mesoporous region of the mesoporous carbon 2. In addition, in the electrode material 1 of this embodiment, the electronically conductive oxide 3a is also fixed to the outer surface of the mesoporous carbon 2.

[0036] The optimal amount of electron-conductive oxide to be attached varies depending on the physical properties of the electron-conductive oxide, such as particle size (or film thickness in the case of a thin film) and surface area, as well as the manufacturing method of the electron-conductive oxide. Therefore, it is determined appropriately within a range that allows for the attachment of a sufficient amount of electrode catalyst particles. For example, when the total amount of electron-conductive oxide and mesoporous carbon is 100% by weight, the optimal amount is between 10% and 80% by weight.

[0037] The size of the electron-conducting oxide within the pores is determined within a range that does not block the pores of the mesoporous carbon 2 and does not hinder mass transfer such as gas. Depending on the pore diameter of the mesoporous carbon 2, the size of the electron-conducting oxide fixed to the inner surface of the pores is preferably between 0.5 nm and 3 nm in particle size.

[0038] The electron-conductive oxide 3a on the outer surface does not substantially contribute to the occlusion of the mesopores, and therefore may be larger than the electron-conductive oxide within the pores. However, in order to reduce electrical resistance, it is preferable that the particle size be small within the range in which the electrode catalyst particles 3b can be dispersed and supported. When an electron-conductive oxide is present on the outer surface, its size is preferably between 0.5 nm and 10 nm.

[0039] The "average particle size of particulate electronically conductive oxides" can be obtained by the average value of the particle diameters of any 20 particulate electronically conductive oxides examined from electron microscope images.

[0040] In Figures 1(a) and 1(b), the electron-conductive oxide 3a is a particulate electron-conductive oxide dispersed and fixed to the mesoporous carbon 2, but it is not limited to this, and the electron-conductive oxide 3a only needs to be fixed to the mesoporous carbon 2. For example, as shown in Figure 1(c), the electron-conductive oxide 3a may not be dispersed but fixed to continuously cover the surface of the mesoporous carbon 2 (particularly the inner surface of the pores). In other words, in the electrode material of the present invention, the form of the fixed electron-conductive oxide may be any form, such as particulate, island-like, or thin film-like, as long as it does not impair the objective of the present invention.

[0041] As the electronically conductive oxide constituting the electronically conductive oxide 3a, an electronically conductive oxide mainly composed of tin oxide is used. Here, in the present invention, "mainly electronically conductive oxide" means (A) one consisting only of the parent oxide, and (B) an oxide doped with other elements, in which the parent oxide is present in an amount of 80 mol% or more. Since electron-conductive oxides mainly composed of tin oxide possess sufficient durability and electron conductivity under the cathode conditions of fuel cells (particularly polymer electrolyte fuel cells), the electrode material of the present invention is preferably used as a cathode for fuel cells.

[0042] As an element, tin (Sn) is thermodynamically stable as an oxide, SnO2, under the cathode conditions of a PEFC, and does not undergo oxidative decomposition. Furthermore, tin oxide has sufficient electronic conductivity and can serve as a support capable of highly dispersed support of electrode catalyst particles (especially noble metal particles). Note that the cathode conditions for a PEFC refer to the conditions at the cathode during normal operation of the PEFC, meaning a temperature of room temperature to approximately 150°C, and the supply of an oxygen-containing gas such as air (oxidizing atmosphere).

[0043] Among oxides mainly composed of tin oxide, niobium-doped tin oxide, which is doped with 0.1 to 20 mol% niobium (Nb), is particularly preferred because it allows for the formation of fuel cell electrodes with superior electrode performance.

[0044] Furthermore, when using the fuel cell electrode of the present invention as an anode, oxides mainly composed of tin oxide are undesirable because they are reduced to metallic Sn under the anode conditions of a PEFC.

[0045] (electrode catalyst particles) The electrode catalyst particles 3b are selectively dispersed and supported on the electron-conductive oxide 3a. Here, "selectively dispersed and supported on the electron-conductive oxide" means that 80% or more, preferably 90% or more, and more preferably 95% or more (including 100%) of all electrode catalyst particles (number of particles) are supported on the electron-conductive oxide. The proportion of electrode catalyst particles supported on the electron-conductive oxide can be evaluated by observing the electrode material to be evaluated with an electron microscope, selecting any electrode catalyst particles (100 or more), and counting the number of particles supported on the electron-conductive oxide and the number of particles supported on the mesoporous carbon.

[0046] The electrode catalyst particles 3b may be either a noble metal catalyst or a non-noble metal catalyst, as long as they have electrochemical catalytic activity for the reduction of oxygen (and oxidation of hydrogen). Preferably, they are selected from noble metals such as Pt, Ru, Ir, Pd, Rh, Os, Au, Ag, and alloys containing these noble metals. Note that "alloys containing noble metals" include "alloys consisting only of the above noble metals" and "alloys consisting of the above noble metals and other metals containing 10% by mass or more of the above noble metals." The "other metals" alloyed with the noble metals are not particularly limited, but Co, Ni, W, Ta, Nb, and Sn can be given as preferred examples, and one or more of these may be used. Furthermore, two or more of the above noble metals and alloys containing noble metals may be used in a phase-separated state. In this specification, the above noble metals and alloys containing these noble metals may be referred to as "electrode catalyst metals" below.

[0047] Among electrode catalyst metals, Pt and alloys containing Pt are particularly suitable for use because they exhibit high electrochemical catalytic activity for oxygen reduction (and hydrogen oxidation) in the temperature range around 80°C, which is the operating temperature of polymer electrolyte fuel cells.

[0048] The shape of the electrode catalyst particles 3b is not particularly limited, and shapes similar to those of known electrode catalyst particles can be used. Specific shapes include spheres, ellipsoids, polyhedra, and core-shell structures. Furthermore, the structure of the electrode catalyst particles 3b is not limited to crystals; it may be amorphous or a mixture of crystalline and amorphous materials.

[0049] The smaller the size of the electrode catalyst particles 3b, the greater the effective surface area for the electrochemical reaction, and therefore the higher the electrochemical catalytic activity tends to be. However, if the size is too small, the electrochemical reaction activity decreases. Therefore, the size of the electrode catalyst particles 3b is preferably 0.5 to 4 nm in average particle diameter.

[0050] In this invention, the "average particle size of electrode catalyst particles" can be obtained by the average value of the particle diameters of 20 electrode catalyst particles examined from electron microscope images. When calculating the average particle size from electron microscope images, if the shape of the fine particles is other than spherical, the length in the direction showing the maximum length of the particle is used as the particle size.

[0051] The amount of electrode catalyst particles supported is determined appropriately, taking into account conditions such as the type of catalyst and the size (thickness) of the electron-conducting oxide support. If the amount of catalyst supported is too small, the electrode performance will be insufficient, and if it is too large, the electrode catalyst particles may aggregate, leading to a decrease in performance.

[0052] When the amount of electrode catalyst particles supported is preferably 0.1 to 60% by mass, more preferably 0.5 to 20% by mass, relative to the total weight of the electrode material, excellent catalytic activity per unit mass is achieved, and the desired electrode reaction activity can be obtained according to the amount of support.

[0053] Furthermore, the amount of electrode catalyst particles supported is typically 3 to 40% by mass relative to the electronically conductive oxide. Within this range, excellent catalytic activity per unit mass is achieved, and the desired electrochemical catalytic activity can be obtained according to the supported amount. If the amount of supported material is less than 3% by mass, the electrode reaction activity is insufficient. If it exceeds 40% by mass, aggregation of the electrode catalyst particles is likely to occur, leading to a decrease in the effective surface area for the electrochemical reactions of oxygen and hydrogen. The amount of supported electrode catalyst particles can be determined, for example, by inductively coupled plasma emission spectrometry (ICP).

[0054] The method for manufacturing the electrode material of the present invention includes steps (1) to (4) as described above. Each step will be described in detail below.

[0055] <Process (1)> Step (1) is a step in which mesoporous carbon and anhydrous alcohol are brought into contact to obtain a dispersion containing mesoporous carbon in which anhydrous alcohol has been introduced into the pores.

[0056] Since anhydrous alcohol is an amphiphilic solvent (dispersion medium), it can be introduced into the pores by bringing it into contact with mesoporous carbon (hydrophobic).

[0057] In the present invention, anhydrous alcohol means alcohol having a purity of 99.5% by volume or more, more preferably 99.7% by volume or more, and particularly preferably 99.8% by volume or more. Furthermore, the alcohol can be any alcohol that has high permeability into the pores of the mesoporous carbon, and specifically, it can be one or more selected from methanol, ethanol, n-propanol, and isopropanol, but ethanol is preferred.

[0058] The method for contacting the mesoporous carbon with anhydrous alcohol is not limited as long as it does not impair the objective of the present invention, but a typical method involves immersing the mesoporous carbon in anhydrous alcohol and stirring it.

[0059] The amount of anhydrous alcohol relative to the mesoporous carbon is arbitrary, as long as it sufficiently fills the pores of the mesoporous carbon. The dispersion containing the mesoporous carbon is then used in the next step (step (2)), and the anhydrous alcohol, which is the solvent (dispersion medium) in step (1), becomes part of the solvent in the mixed solution of step (2).

[0060] <Process (2)> Step (2) is a step in which a dispersion containing mesoporous carbon into which anhydrous alcohol obtained in step (1) has been introduced is mixed with a tin alkoxide solution containing the electron-conductive oxide tin alkoxide and a water / alcohol solvent to obtain a mixed solution, and then the solvent is distilled off from the mixed solution to obtain a dried product in which hydrolysates of the tin alkoxide are fixed to the inner and outer surfaces of the pores of the mesoporous carbon.

[0061] As described above, water does not easily penetrate the pores of untreated mesoporous carbon. However, in the manufacturing method of the present invention, mesoporous carbon in which amphiphilic anhydrous alcohol has been introduced into the pores in step (1) is used. By mixing a dispersion containing this mesoporous carbon with a tin alkoxide solution and a water / alcohol solvent (a mixed solvent of water and alcohol), it becomes possible to introduce tin alkoxide (hydrophobic) and water (hydrophilic) into the pores of the mesoporous carbon together with the alcohol solvent.

[0062] The ratio of water to alcohol in the mixed solvent is determined appropriately within a range that does not impair the objective of the present invention. In order to reliably generate hydrolysates in the pores of mesoporous carbon, the proportion of water in the mixed solution in step (2) in the total 100% by volume of water and alcohol is 0.1% by volume or more and 10% by volume or less (preferably 0.5% by volume or more and 5% by volume or less). If the proportion of water in the solvent is too high, the hydrolysis reaction proceeds rapidly in the liquid, making the resulting hydrolysates more likely to aggregate, and reducing the proportion of tin alkoxide that reacts within the mesoporous carbon pores, thus tending to result in a smaller amount of hydrolysates produced within the pores. The amount of alcohol in the mixed solution is the sum of the amount of alcohol added as a water / alcohol solvent in step (2) and the amount of anhydrous alcohol used as the solvent (dispersion medium) in step (1).

[0063] While it is not entirely clear why the above water concentration is suitable in step (2), it can be inferred as follows. Since tin alkoxide is an alkoxide with relatively low reactivity with water, the hydrolysis reaction does not proceed easily when the concentration of water in the mixed solution is low. Therefore, if the proportion of water in the mixed solution is within the above range, the hydrolysis reaction in the liquid does not proceed substantially, and the tin alkoxide and water are introduced into the pores of the mesoporous carbon unreacted. When the solvent is removed by distillation in this state, the alcohol is preferentially removed, so the concentrations of tin alkoxide and water become relatively larger. As a result, the hydrolysis reaction of tin alkoxide proceeds (both inside and outside the pores of the mesoporous carbon), and the hydrolyzed tin alkoxide can be retained on the surface of the mesoporous carbon (inside and outside the pores) and dried.

[0064] The alcohol used in the water / alcohol solvent in step (2) may be one or more selected from methanol, ethanol, n-propanol, and isopropanol, but it is preferable that it be the same as the anhydrous alcohol used in step (1). That is, if anhydrous ethanol was used in step (1), it is preferable to use ethanol in step (2).

[0065] As tin alkoxides, tin methoxide, tin ethoxide, tin propoxide, tin butoxide, tin methoxyethoxide, and tin ethoxyethoxide can be used. Among these, tin ethoxide is preferred.

[0066] For example, if the target electron-conducting oxide is a Sn oxide containing niobium oxide, then niobium alkoxide can be used together with the above-mentioned tin alkoxide. As niobium alkoxide, niobium methoxide, niobium ethoxide, niobium propoxide, niobium butoxide, niobium methoxyethoxide, and niobium ethoxyethoxide can be used. Among these, niobium ethoxide is preferred.

[0067] When the target electronically conductive oxide is a sn oxide containing niobium oxide, as shown in the examples, it is preferable to first obtain a dried product in which hydrolyzed tin alkoxide is fixed to the inner and outer pore surfaces of mesoporous carbon, then disperse the obtained dried product in a niobium alkoxide solution and distill off the solvent to obtain a dried product. It is preferable that the solvent in the niobium alkoxide solution is the same solvent as the mixed solution containing tin alkoxide. That is, if the solvent in the mixed solution containing tin alkoxide is ethanol, it is preferable that the solvent in the niobium alkoxide solution is also ethanol.

[0068] The amount and concentration of mesoporous carbon should be determined appropriately within a range that allows sufficient fixation of the resulting hydrolysates. For example, using the electron-conducting oxide derived from the final raw material alkoxide as a reference, the amount should be set to be between 10% and 80% by weight when the total of the electron-conducting oxide and mesoporous carbon is set to 100% by weight.

[0069] The raw material alkoxide solution can contain any non-aqueous organic solvent that does not react with the raw material alkoxide, such as acetone, acetylacetone, toluene, xylene, or kerosene.

[0070] The method of drying by distilling off the solvent is optional as long as it does not impair the objective of the present invention, but distillation of the solvent by reduced pressure is preferred. A specific example is drying under reduced pressure using a vacuum device such as a rotary evaporator.

[0071] <Process (3)> Step (3) is a step in which the dried material obtained in step (2) is heat-treated to obtain a porous composite support in which an electron-conducting oxide is fixed to the inner surface and outer surface of the pores of the mesoporous carbon.

[0072] As described above, the dried material obtained in step (2) retains hydrolyzed products formed by hydrolysis on the surface of the mesoporous carbon (inner and outer pore surfaces). Hydrolyzed products are hydroxides and non-stoichiometric oxides, which have low crystallinity and poor adhesion to the mesoporous carbon support. However, heat treatment improves the crystallinity of the electron-conducting oxides, causing them to adhere strongly (fix) to the mesoporous carbon.

[0073] The atmosphere during heat treatment should be one in which the hydrolysis products of the alkoxide compound are converted to oxides without affecting the electron-conducting oxides or carbon supports. Typically, this is an inert gas atmosphere such as nitrogen, helium, or argon.

[0074] The heat treatment temperature should be above the temperature at which the crystallinity of the electronically conductive oxide improves, and should be 350°C or higher, preferably 500°C or higher, and more preferably 550°C or higher. Furthermore, since tin oxide, the main component of the electronically conductive oxide, becomes metallic tin at temperatures close to 700°C, the upper temperature limit should be 650°C or lower, preferably 630°C or lower.

[0075] The heat treatment time should be set to a duration that increases crystallinity without causing aggregation, and while it depends on the heat treatment temperature, it is usually around 20 minutes to 3 hours.

[0076] <Process (4)> Step (4) is a step in which the porous composite support obtained in step (3) (mesoporous carbon in which electron-conductive oxides are fixed to the inner and outer surfaces of the pores) and the electrode catalyst precursor are mixed until homogeneous, and the solvent is removed by distillation, and the resulting dried product is heat-treated in an inert gas atmosphere.

[0077] In step (3), a dried product is obtained in which electrode catalyst particle precursors are supported on an electron-conducting oxide in a porous composite support (mesoporous carbon with an electron-conducting oxide fixed to its surface). The electrode catalyst particles supported on the porous composite support contained in the obtained dried product may contain metal oxides in an unstoichiometric ratio and have low activity as is. Therefore, the electrochemical catalytic activity of the metal that will become the electrode catalyst is activated by heat treatment in an inert atmosphere such as nitrogen or argon, or a reducing atmosphere containing hydrogen.

[0078] The electrode catalyst precursor in step (3) is not limited as long as it does not impair the objective of the present invention; however, depending on the electrode catalyst precursor, the objective of the present invention may not be achieved in terms of the particle size and dispersibility of the electrode metal particles.

[0079] Acetylacetonate compounds are suitable as electrode catalyst precursors for obtaining highly dispersed electrode catalyst particles with small particle size. The acetylacetonate compound, which is the electrode catalyst precursor, is supported on a porous composite support, and then directly converted into electrode catalyst particles. This method is expected to improve catalytic activity because the electrode catalyst precursor does not contain residual impurities. In the acetylacetonate method, an acetylacetonate compound, which is an electrode catalyst, is dissolved in a suitable solvent such as dichloromethane. A porous composite support is dispersed in this solution, and the electrode catalyst precursor is supported by stirring and distillation of the solvent. This method avoids the inclusion of impurities such as chlorine and sulfur, and allows for highly dispersed support of electrode catalyst particles with a uniform nano-size particle size distribution. Furthermore, since strong oxidizing or reducing agents are not used in the solution, degradation of the electron-conducting oxides and mesoporous carbon, which constitute the porous composite support, can be avoided.

[0080] Examples of acetylacetonate compounds used as electrode catalysts include acetylacetonates of noble metals such as Pt, Ru, Ir, Pd, Rh, Os, Au, and Ag, and one or more of these can be used. Any organic solvent capable of dispersing the noble metal acetylacetonate is acceptable as a solvent; typical examples include dichloromethane and acetylacetone.

[0081] One method for supporting electrode catalyst nanoparticles using the acetylacetonate method involves placing a conductive auxiliary material on which an electronically conductive oxide is supported and a noble metal acetylacetonate in a designated container, and stirring it with an ultrasonic stirring device while cooling it with ice until all the solvent has evaporated.

[0082] The heat treatment conditions are appropriately selected depending on the type of electron-conducting oxide and the metal or precursor used as the electrode catalyst. For example, in the case of electron-conducting oxides that are unstable in a reducing atmosphere, such as tin oxide, the temperature is usually 180-400°C, preferably 200-250°C, when the electrode catalyst is Pt or a Pt alloy. If the temperature is too low, the activation of the metal electrode catalyst will be insufficient, and if the temperature is too high, the electrode catalyst particles will aggregate, resulting in a problem where the effective reaction surface area becomes too small. Water vapor may be added to the atmosphere as needed.

[0083] The present invention has been described above, but these are illustrative examples, and various other configurations can be adopted. The embodiments disclosed herein are illustrative and not restrictive in all respects. In particular, matters not explicitly disclosed in this disclosure, such as operating conditions, various parameters, dimensions, weight, and volume of components, do not deviate from what is normally practiced by those skilled in the art, and values ​​that can be easily anticipated by those skilled in the art can be adopted. [Examples]

[0084] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these. In the following, mesoporous carbon may be referred to as "MC".

[0085] 1. Preparation of electrode materials The following electrode materials were manufactured as the electrode materials for the examples.

[0086] The porous carbon, raw material alkoxide (electronically conductive oxide precursor), electrode catalyst precursor, and solvent used are as follows. <Porous Carbon> As the porous carbon, the following mesoporous carbon (MC) (Toyo Tanso Co., Ltd., "Porous Carbon CNovel MJ(4)010 (Grade Name)") was used. Design pore diameter: 10nm Specific surface area: 1100m 2 / g Total pore volume: 2.0 mL / g Micropore volume: 0.4 mL / g Particle size: 100 mesh pass (to be crushed before use) <Electronically conductive oxide precursor> As the Sn alkoxide, tin ethoxide (Sn(OC2H5)4) (Strem Chemicals INC) was used, and as the Nb alkoxide, niobethoxide (Nb(OC2H5)5) (Sigma Aldrich) was used. <Electrode catalyst precursor> Pt acetylacetonate (Pt(C5H7O2)2, Platinum(II) acetylacetonate, 97%, Sigma Aldrich) was used as the electrode catalyst precursor (noble metal precursor compound). Note that Pt acetylacetonate may be referred to as Pt precursor (Pt(acac)2) below. <Solvent (Dispersion Medium)> Anhydrous ethanol (Kishida Chemical Co., Ltd. Special Grade Ethanol (99.5%))

[0087] As shown in the flowchart in Figure 2, a porous composite support (sometimes referred to as "electrode material (without electrode catalyst)") was manufactured by fixing niobium-doped tin oxide to mesoporous carbon (MC).

[0088] <Experimental Example A1> Step (1): 183.7 mg of the above-mentioned mesoporous carbon (MC), which is the carrier skeleton material, was added to 50 mL of anhydrous ethanol and thoroughly mixed so that the anhydrous ethanol was introduced into the pores of the MC. Step (2): A mixed solution was obtained by adding anhydrous ethanol to the MC and tin ethoxide solution (375 mg of tin ethoxide dissolved in 6 mL of acetylacetone) and thoroughly mixing it with a mixed solvent of ethanol and water. The molar ratio of the contents of the mixed solution was tin ethoxide:water:MC = 1.8:55.6:15.3, and the amount of solvent in the mixed solution was 100 mL (92 mL of ethanol (including the anhydrous ethanol from step (1)), 2 mL of water, and 6 mL of acetylacetone). Step (3): The obtained mixed solution was subjected to ultrasonic stirring under reduced pressure using a vacuum pump, control unit, and rotary evaporator equipped with a rotation function to evaporate the solvent, thereby obtaining a dry powder in which tin ethoxide was uniformly adsorbed on the MC surface (inner and outer pore surfaces). Next, the obtained dry powder was dispersed again in ethanol, and 11.663 mg of niobethoxide dissolved in 203.4 μL of ethanol was added. The mixture was dried under reduced pressure until all the solvent evaporated, and a dry powder in which tin ethoxide and niobethoxide were adsorbed on the MC surface (inner and outer pore surfaces) was obtained. Step (4): After grinding the obtained dry powder, heat treatment is performed at 400°C for 2 hours in an N2 atmosphere, and then allowed to cool naturally to room temperature to fix niobium-doped tin oxide to the MC, which constitutes the electrode material of Experimental Example A1 (electrode catalyst unsupported, "Sn 0.98 Nb 0.02 We obtained "O2 / MC-400℃". Furthermore, in the electrode material of experimental example A1, the oxide (Sn 0.98 Nb 0.02 The concentration is 60 wt% (O2) (amount added).

[0089] <Experimental Example A2> The electrode material for Experimental Example A2 (without electrode catalyst support, "Sn") was the same as in Experimental Example A1, except that the heat treatment conditions for the dried powder on which the raw material alkoxides (tin ethoxide and niob ethoxide) were adsorbed were changed to 400°C for 2 hours, followed by 500°C for 30 minutes. 0.98 Nb0.02 "O2 / MC-500 °C") was obtained.

[0090] <Experimental Example A3> The electrode material of Experimental Example A3 (without electrode catalyst support, "Sn 0.98 Nb 0.02 O2 / MC-600 °C") was obtained in the same manner as Experimental Example A1, except that the heat treatment conditions of the dried powder adsorbed with the starting alkoxides (tin ethoxide and niobium ethoxide) were changed to 400 °C for 2 hours and then 600 °C for 30 minutes.

[0091] <Experimental Example A4> The electrode material of Experimental Example A4 (without electrode catalyst support, "Sn 0.98 Nb 0.02 O2 / MC-700 °C") was obtained in the same manner as Experimental Example A1, except that the heat treatment conditions of the dried powder adsorbed with the starting alkoxides (tin ethoxide and niobium ethoxide) were changed to 400 °C for 2 hours and then 700 °C for 30 minutes.

[0092] <Experimental Example A5> Oxide (Sn 0.98 Nb 0.02 O2) 20 wt% (charge amount)), the electrode material of Experimental Example A5 (without electrode catalyst support) was obtained in the same manner as Experimental Example A3 (60 wt% (charge amount)).

[0093] <Experimental Example A6> Oxide (Sn 0.98 Nb 0.02 O2) 40 wt% (charge amount)), the electrode material of Experimental Example A6 (without electrode catalyst support) was obtained in the same manner as Experimental Example A3. [[ID=4 =3]]

[0094] <Experimental Example A7> Oxide (Sn 0.98 Nb 0.02 O2) 75 wt% (charge amount)), the electrode material of Experimental Example A7 (without electrode catalyst support) was obtained in the same manner as Experimental Example A3.

[0095] 2. Evaluation of electrode material (without electrode catalyst support) The crystallinity of the electrode materials (without electrode catalyst support) in experimental examples A1 to A4 was evaluated by X-ray diffraction, and their microstructure was evaluated by electron microscopy. Figure 3 shows the XRD profiles for heat treatment temperatures of 600°C (Experimental Example A3), 700°C (Experimental Example A4), and, for reference, for the untreated XRD profile. Furthermore, Figure 4 shows FE-SEM and TEM images at a heat treatment temperature of 600°C (Experimental Example A3), Figure 5 shows the FE-SEM image at a heat treatment temperature of 700°C (Experimental Example A4), and Figure 6 shows the limited-field electron diffraction at heat treatment temperatures of 400°C (Experimental Example A1) and 500°C (Experimental Example A2).

[0096] As shown in Figure 3, at a heat treatment temperature of 600°C (Experimental Example A3), a clear XRD signal indicating SnO2 crystals was observed, and in Figure 4, the presence of fine particles other than MCs was also confirmed. Furthermore, although the XRD signals indicating SnO2 crystals were not as clear at heat treatment temperatures of 400°C (Experimental Example A1) and 500°C (Experimental Example A2) compared to 600°C (not shown), selected-field electron diffraction shown in Figure 6 confirmed that SnO2 crystals were also present at heat treatment temperatures of 400°C (Experimental Example A1) and 500°C (Experimental Example A2), and that increasing the heat treatment temperature improved the crystallinity of SnO2.

[0097] On the other hand, at a heat treatment temperature of 700°C (Experimental Example A4), it was confirmed that very large particles were generated outside the MC, as shown in Figure 5. Furthermore, as shown in Figure 3, at a heat treatment temperature of 700°C (Experimental Example A4), a peak of metallic Sn was observed along with an XRD signal indicating SnO2 crystals. Therefore, it was concluded that the high-temperature heat treatment at 700°C caused tin oxide to react with carbon, reducing the tin oxide and causing the carbon to disappear, eliminating the mesostructure of the MC and promoting the aggregation of metallic tin.

[0098] Figure 7 shows the results of STEM / EDS mapping evaluations for Experimental Examples A3 and A5-A7, in which the amount of oxide deposition was varied at a heat treatment temperature of 600°C. In experimental examples A3 (20 wt%) and A5 (40 wt%), the Sn signals were separated, whereas in experimental examples A6 (60 wt%) and A7 (75 wt%), the Sn signals were in contact. This led to the conclusion that when the amount of tin oxide supported is high, the particles come into contact with each other. On the other hand, even when the amount of tin oxide supported was increased, no significant aggregation was observed. From these results, it was concluded that the porous structure of mesoporous carbon suppresses the growth of tin oxide particles and inhibits aggregation.

[0099] Next, using experimental example A6 (tin oxide adhesion rate 40 wt%), the results of observing the microstructure within the mesopores of the micromolecule are shown in Figure 8. Figure 8 (right) shows images of the same area taken with different STEM focus settings: (a) is focused on the foreground (near the mesopore surface), (b) is inside the mesopore, and (c) is inside the mesopore. The presence of particles within a circle of approximately 10 nm, which is the pore size of the micromolar (MC), confirmed that tin oxide particles are supported within the mesopores. Furthermore, the observation of lattice patterns from different particles with each change in focus indicated that the tin oxide was present in layers (see left image in Figure 8), confirming that it could be dispersed and supported deep within the mesopores without agglomerating near the surface.

[0100] 3. Fabrication and microstructure evaluation of electrode material (Pt-supported) As shown in the flowchart in Figure 9, Pt catalyst particles, which are electrode catalyst particles, were supported on the electrode materials (without electrode catalyst) of Experimental Examples A3 and A5-A7 by the platinum acetylacetonate method. The amount of Pt precursor (Pt(acac)2) was adjusted so that the Pt content was 30 wt%. In a round-bottom flask, the electrode material of Experimental Example 1 (without electrode catalyst support), consisting of MC with niobium-doped tin oxide fixed to it, and the Pt precursor (Pt(acac)2) were added, and then acetone was added to dissolve them. Next, while applying ultrasonic waves in an ultrasonic cleaner, the mixture was reduced in a rotary evaporator and rotated until all the solvent evaporated to obtain a dry powder. Then, the obtained dry powder was heat-treated in an N2 atmosphere at 210°C for 3 hours and at 240°C for 3 hours to obtain the electrode materials of Experimental Examples A3 and A5-A7 ("Pt / Sn 0.98 Nb 0.02 O2 / MC was obtained.

[0101] <Comparative Example 1> As a comparative example, an electrode material (Pt / MC) for Comparative Example 1 was obtained by supporting Pt on MC using the platinum acetylacetonate method.

[0102] (2) Electrode material (Pt supported) Electrode material (Pt / Sn 0.98 Nb 0.02 The STEM / EDS results for O2 / MC are shown. As shown in Figure 10, it was confirmed that in the electrode material of experimental example A3, Pt nanoparticles were dispersed and supported on the MC via Sn(Nb)O2. Although not shown, the same was true for the electrode materials of experimental examples A5 to A7. In comparative example 1, it was confirmed that the Pt nanoparticles were directly supported on the MC.

[0103] 4. Electrochemical evaluation (half-cell) 4-1. Evaluation of Cyclic Voltammetry (CV) The electrode materials for Experimental Examples A3, A5-7, and Comparative Example 1 were evaluated by cyclic voltammetry (CV). The electrochemical surface area (ECSA) was calculated from the hydrogen adsorption amount obtained from the CV. Note that ECSA corresponds to the effective surface area of ​​Pt contained in the electrode material.

[0104] The fuel cell electrodes for evaluation were fabricated using the following procedure. First, a mixture of 19 mL of ultrapure water and 6 mL of 2-propanol was added to a sample bottle containing the electrode material powder. Subsequently, 100 μL of 5% Nafion dispersion was added, and the sample bottle was then immersed in ice water and ultrasonically stirred for 30 minutes to obtain the electrode material dispersion. The amount of electrode material powder was such that when 10 μL of the electrode material dispersion was dropped onto the electrode, the Pt mass per unit area on the electrode was 17.3 μg. -Pt ·cm -2 The following procedure was followed: 10 μL of the prepared electrode material dispersion was dropped onto the Au disk electrode using a micropipette, and the mixture was dried in a constant temperature incubator at 60°C for approximately 15 minutes to form a Nafion film, thereby fixing the electrode material onto the Au electrode and obtaining a fuel cell electrode (working electrode) for evaluation.

[0105] The measurement conditions for CV are as follows. Assuming that one hydrogen atom is adsorbed per platinum atom, the value is 210 μC / cm². 2 This will result in the amount of electricity. Measurement: Three-electrode cell (working electrode: fuel cell electrode for evaluation, counter electrode: Pt, reference electrode: Ag / AgCl) Electrolyte: 0.1M HClO4 (pH: approx. 1) Measurement potential range: 0.05~1.2V (reversible hydrogen electrode reference) Scanning speed: 50 mV / s Hydrogen adsorption amount: Calculated from the peak area showing hydrogen adsorption of 0.05~0.4V. Electrochemical surface area (ECSA): Calculated using the following formula. ECSA=(hydrogen adsorption amount)[μC] / 210[μC / cm 2 ]

[0106] 4-2. Evaluation of ORR activity The ORR activity was evaluated for the electrode materials of Experimental Examples A3, A5-7 and Comparative Example 1. ORR activity is determined by linear sweep voltammetry (LSV) using the rotating disk electrode method (RDE method), and the resulting activation-controlled current (i k The Mass activity (activity per unit Pt mass) calculated based on the above was used as the indicator. Mass holding = i k Pt mass on the electrode Activation dominant current (i k ) refers to the current-potential curve obtained by rotational electrode measurement, where i is set at any potential. -1 and ω -1 / 2 The intercept was obtained by plotting the data and creating a Koutecky-Levich plot, then extrapolating the resulting straight line. The specific procedure is as follows: First, bubble O2 at 50 mL / min for 30 minutes, then 0.2V RHE From the noble direction, at 10mV / s, 1.20V RHE The potential was scanned up to and measured. During the measurement, O2 was purged at 50 mL / min. RHE This is the potential relative to the reversible hydrogen electrode (RHE).

[0107] Electrode materials (Pt / Sn) for experimental examples A3, A5~7 0.98 Nb 0.02 CV and LSV were performed on O2 / MC and Comparative Example 1 (Pt / MC), and the electrochemical surface area (ECSA) and mass activity (j m (0.9V RHE )), Specific activity(j s The following was calculated. The results are summarized in Table 1.

[0108] [Table 1]

[0109] 4-3. Start-up / Shutdown Cycle Test The electrode materials for Experimental Examples A3, A5-7 and Comparative Example 1 underwent start-stop cycle testing using the method recommended by the Fuel Cell Commercialization Promotion Council (FCCJ) (Proposal for Goals, Research and Development Issues and Evaluation Methods for Solid Polymer Fuel Cells, published January 2011). The start-stop cycle test is a cycle test that accelerates carbon corrosion, specifically the 1.0-1.5V shown in Figure 11. RHE The rectangular wave is applied for 2 seconds per cycle, and the degradation behavior of the electrode catalyst after the cycle test is evaluated as an ECSA change.

[0110] Figure 12 shows the ECSA change (relative value) of the electrode materials for experimental examples A3, A5-7 and comparative example 1 during the start-stop cycle test (up to 60,000 cycles). As can be seen from Figure 12, the electrode using the electrode material of Comparative Example 1 (Pt / MC, 0 wt%) showed a significant decrease in ECSA immediately after the start-stop cycle test, reaching about 50% of the initial value after 10,000 cycles, and the test could not be continued until 20,000 cycles (ECSA retention rate was almost 0). In contrast, the electrode materials (Pt / Sn) of experimental examples A3, A5~7 0.9 Nb 0.1 With electrodes using O2 / MC, the decrease in ECSA was gradual, and all were capable of being tested for up to 60,000 cycles. In particular, it was confirmed that approximately 30% of the initial value could be retained in experimental example A3 (oxide adhesion rate, 60 wt%), and approximately 55% of the initial value could be retained in experimental example A7 (oxide adhesion rate, 75 wt%). These results demonstrate that degradation can be suppressed by supporting Pt via an oxide rather than in direct contact with MC. [Industrial applicability]

[0111] The electrode material of the present invention provides fuel cell electrodes with excellent electrode catalytic activity, electronic conductivity, gas diffusion properties, and durability, making it promising as an electrode component for polymer electrolyte fuel cells used in the automotive, power, gas, and home appliance industries. In particular, it is expected to be used in fuel cell vehicles where load fluctuations are severe. [Explanation of symbols]

[0112] 1 Electrode material 2. Porous carbon (mesoporous carbon) 2a Inner surface of pores 2b Outer surface 3a Electronically conductive oxides 3b Electrocatalyst particles P pores (mesopores)

Claims

1. A method for producing an electrode material comprising a porous composite carrier made of mesoporous carbon and an electronically conductive oxide mainly composed of tin oxide fixed to the inner and outer surfaces of the pores of the mesoporous carbon, and electrode catalyst particles supported on the porous composite carrier, the method comprising the following steps (1) to (4). Step (1): A step of bringing mesoporous carbon into contact with anhydrous alcohol to obtain a dispersion containing mesoporous carbon in which anhydrous alcohol has been introduced into the pores. Step (2): A mixture is obtained by mixing the dispersion containing mesoporous carbon into which anhydrous alcohol obtained in Step (1), the tin alkoxide solution containing the electron-conductive oxide tin alkoxide, and a water / alcohol solvent to obtain a mixed solution. The solvent is then removed from the mixed solution by distillation to obtain a dried product in which hydrolysates of tin alkoxide are fixed to the inner and outer surfaces of the pores of the mesoporous carbon. Step (3): A step in which the dried material obtained in step (2) is heat-treated to obtain a porous composite carrier in which an electron-conducting oxide is fixed to the inner surface and outer surface of the pores of the mesoporous carbon. Step (4): A process in which the porous composite support obtained in step (3) and the solution containing the electrode catalyst precursor are mixed until homogeneous, and the solvent is removed by distillation, and the resulting dry product is heat-treated in an inert gas atmosphere.

2. The method for producing an electrode material according to claim 1, wherein in step (1), the anhydrous alcohol is one or more selected from methanol, ethanol, n-propanol, and isopropanol.

3. A method for producing an electrode material according to claim 1, wherein in step (2), a dried product is obtained in which hydrolyzed tin alkoxide is fixed to the inner surface and outer surface of the pores of the mesoporous carbon, and then the obtained dried product is dispersed in a niobalkoxide solution and the solvent is removed by distillation to obtain a dried product.

4. A method for producing an electrode material according to any one of claims 1 to 3, wherein in step (2), the proportion of water in the mixed solution in a total of 100% by volume of water and alcohol (including the anhydrous alcohol content in the dispersion) is 0.1% by volume or more and 10% by volume or less.

5. The method for manufacturing an electrode material according to claim 1, wherein in step (3), the heat treatment temperature is 350°C or more and 650°C or less.

6. The method for producing an electrode material according to claim 1, wherein in step (4), the electrode catalyst precursor is a noble metal acetylacetonate.

Images