Method for producing noble metal-containing material, noble metal-containing material, membrane electrode assembly, and fuel cell

Abstract

To provide a method capable of easily producing, with fewer steps, a material in which minute noble metal atoms are dispersed in a carrier including a carbonaceous material and which can exhibit sufficient catalytic performance.SOLUTION: A method for producing a noble metal-containing material includes: preparing a mixed liquid which includes a carbon raw material, a polyoxometalate compound including noble metal atoms, and a hydrophilic solvent including water, the carbon raw material being dissolved or dispersed in the hydrophilic solvent, the polyoxometalate compound being dissolved in the hydrophilic solvent; taking out a solid mixture including the carbon raw material and the polyoxometalate compound from the mixed liquid; and firing the solid mixture and thereby forming a noble metal-containing material including a carrier including a carbonaceous material and metal particles including the noble metal atoms.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a noble metal-containing material, a noble metal-containing material, a membrane electrode assembly, and a fuel cell.

Background Art

[0002] As a material for forming an electrode catalyst layer constituting a membrane electrode assembly (MEA) of a fuel cell, a platinum-supported carbon material (Pt / C) is widely applied. Pt / C is generally manufactured by a multi-step process including forming a carbonaceous material by carbonization of a carbon raw material, immersing the carbonaceous material in a solution containing platinum, and depositing platinum particles on the surface of the carbonaceous material by reducing platinum. A method has also been proposed in which platinum particles are supported on a carbonaceous material having a hollow structure by utilizing a photocatalytic reaction with titanium oxide particles (Non-Patent Document 1).

[0003] On the other hand, the present inventor has heretofore found that a polyoxometalate compound containing noble metal atoms such as platinum, and a fired body thereof have photocatalytic activity for producing hydrogen (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present disclosure relates to a method capable of easily manufacturing, in fewer steps, a material in which minute metal particles containing noble metal atoms are dispersed in a carrier containing a carbonaceous material and which can exhibit sufficient catalytic performance.

Means for Solving the Problems

[0007] The present disclosure includes the following. [1] Preparing a mixed solution containing a carbon raw material, a polyoxometalate compound containing noble metal atoms, and a hydrophilic solvent containing water, wherein the carbon raw material is dissolved or dispersed in the hydrophilic solvent and the polyoxometalate compound is dissolved in the hydrophilic solvent; Taking out a solid mixture containing the carbon raw material and the polyoxometalate compound from the mixed solution; By firing the solid mixture, forming a noble metal-containing material including a carrier containing a carbonaceous material generated by carbonization of the carbon raw material and metal particles containing the noble metal atoms supported on the carrier; including, the polyoxometalate compound has a metal-substituted polyoxometalate and its counter ion, the metal-substituted polyoxometalate has a polyoxometalate having one or more defect sites and the noble metal atoms introduced into the defect sites, A method for producing a noble metal-containing material. [2] The method according to [1], wherein the carbon raw material includes an organic compound containing nitrogen atoms. [3] The method according to [1] or [2], wherein the carbon raw material includes nanofibers having a fiber diameter of less than 1 μm, microfibers having a fiber diameter of 1 μm or more and less than 1 mm, or a combination thereof. [4] The method according to [3], wherein the carbon raw material includes the nanofibers, and the nanofibers include chitosan nanofibers, chitin nanofibers, or a combination thereof. [5] The method according to any one of [1] to [4], wherein the noble metal atoms include platinum, palladium, ruthenium, or a combination thereof. [6] Preparing a noble metal-containing material including a carrier containing a carbonaceous material and metal particles containing noble metal atoms by the method according to any one of [1] to [5]; Forming an electrode catalyst layer including the noble metal-containing material; A method for manufacturing an electrode catalyst layer, including: [7] A carrier including a carbonaceous material and transition metal atoms; Metal particles containing noble metal atoms supported on the carrier; A noble metal-containing material, including: [8] The noble metal-containing material according to [7], which is fibrous. [9] The noble metal-containing material according to [7] or [8], wherein the particle size of the metal particles is 100 nm or less.

[10] An electrolyte membrane and an electrode catalyst layer disposed on the electrolyte membrane, wherein the electrode catalyst layer includes the noble metal-containing material according to any one of [7] to [9]. A membrane electrode assembly for a fuel cell.

[11] A fuel cell including the membrane electrode assembly for a fuel cell according to

[10] . [Advantages of the Invention]

[0008] A material in which fine metal particles containing noble metal atoms are dispersed in a carbon material and which can exhibit sufficient catalytic performance can be easily manufactured in fewer steps. Biomass materials such as chitin contained in waste can also be effectively utilized. [Brief Description of the Drawings]

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0010] The present invention is not limited to the following examples.

[0011] FIG. 1 is a flowchart showing an example of a method for producing a noble metal-containing material. The method shown in FIG. 1 includes a step S1 of preparing a mixed solution containing a carbon raw material, a polyoxometalate compound containing noble metal atoms, and a hydrophilic solvent containing water; a step S2 of taking out a solid mixture containing the carbon raw material and the polyoxometalate compound from the mixed solution; and a step S3 of forming a noble metal-containing material by firing the solid mixture.

[0012] The carbon raw material contained in the mixed solution prepared in step S1 is a material that forms a carbonaceous material by firing. The carbon raw material may be, for example, a polysaccharide, and examples thereof include cellulose, lignocellulose, chitosan, chitin, pectin, and starch. The carbon raw material may contain an organic compound containing a nitrogen atom. The organic compound containing a nitrogen atom is likely to adsorb the polyoxometalate compound by electrostatic interaction, which is advantageous for the formation of a noble metal-containing material in which fine metal particles containing noble metal atoms are uniformly dispersed. The organic compound containing a nitrogen atom may be a compound having an amino group or an amide group, and examples thereof include chitosan, chitin, protein, melamine resin, urea resin, and polyamine (an aliphatic compound having two or more amino groups).

[0013] The carbon raw material may be fibrous. In particular, the carbon raw material may include nanofibers having a fiber diameter of less than 1 μm, microfibers having a fiber diameter of 1 μm or more and less than 1 mm, or a combination thereof. By using a fibrous carbon raw material having a minute fiber diameter, fine metal particles containing noble metal atoms can be uniformly dispersed, and a fibrous noble metal-containing material having a large specific surface area can be easily obtained. In the present specification, the fiber diameter means the maximum value of the distance between two parallel straight lines sandwiching a fiber cross section perpendicular to the longitudinal direction of the fiber.

[0014] The nanofibers as the carbon raw material may be one or more selected from chitosan nanofibers, chitin nanofibers, and cellulose nanofibers, and may include chitosan nanofibers, chitin nanofibers, or a combination thereof. These nanofibers can be obtained from waste containing biomass materials and can also contribute to the effective utilization of waste.

[0015] The polyoxometalate compound has a metal-substituted polyoxometalate and its counter ion. The metal-substituted polyoxometalate has a polyoxometalate having one or more defect sites and noble metal atoms introduced into the defect sites. The number of noble metal atoms introduced into one defect site is not particularly limited, and can be, for example, one or two. When one metal-substituted polyoxometalate has a plurality of noble metal atoms, those noble metal atoms may be the same or different from each other.

[0016] Polyoxometalates are generally anions formed by the condensation of oxoacids of transition metal atoms. Polyoxometalates may contain heteroatoms, which are elements different from transition metal atoms. Polyoxometalates containing heteroatoms include, for example, a heteroatom, a plurality of transition metal atoms, and a plurality of oxygen atoms bonded to the heteroatom or transition metal atoms. In polyoxometalates, generally, a plurality of transition metal atoms are bonded to the heteroatom via oxygen atoms. The number of heteroatoms contained in one molecule of polyoxometalate is usually one. Polyoxometalate compounds may form hydrates.

[0017] Polyoxometalates can be, for example, of the Keggin type, Dawson type, Anderson type, or Waugh type, but in the present disclosure, polyoxometalates are most typically of the Keggin type. A mononuclear metal-substituted polyoxometalate having a Keggin-type polyoxometalate with one defective site and having one noble metal atom introduced therein can be represented, for example, by the formula (1): [XM 11 O 39 {M 1 (L 1 ) p}] n- ···(1) In the formula (1), X represents a heteroatom, M represents a transition metal atom, M 1 represents a noble metal atom, L 1 represents an organic ligand coordinated to the substituted metal atom M 1 , p represents 1 or 2, and n represents an integer from 1 to 10. A binuclear metal-substituted polyoxometalate having a Keggin-type polyoxometalate with one defective site and having two noble metal atoms introduced therein can be represented, for example, by the formula (2): [XM 11 O 39 {M 1 (L 1 ) p}}{M 2 (L 2 ) q}]n- ···(2) is represented by. In formula (2), X represents a heteroatom, M 1 and M 2 each independently represent a noble metal atom, L 1 represents an organic ligand coordinated to the substituted metal atom M 1 , L 2 represents an organic ligand coordinated to the substituted metal atom M 2 . p and q each independently represent 1 or 2, and n represents an integer from 1 to 10. In formulas (1) and (2), when the organic ligand L 1 is a monodentate ligand, p is 2, and when the organic ligand L 1 is a bidentate ligand, p is 1. In formula (2), when the organic ligand L 2 is a monodentate ligand, q is 2, and when the organic ligand L 2 is a bidentate ligand, q is 1. Here, the bidentate ligand is used as a term including chelate ligands.

[0018] The transition metal atom constituting the polyoxometalate may be, for example, a tungsten atom (W) or a molybdenum atom (Mo). The heteroatom constituting the polyoxometalate can be selected from, for example, a phosphorus atom (P), a silicon atom (Si), a germanium atom (Ge), an aluminum atom (Al), and a boron atom (B).

[0019] The noble metal atom introduced into the defect site of the polyoxometalate may be, for example, at least one selected from platinum, palladium, rhodium, iridium, and ruthenium. The noble metal atom may be platinum, palladium, ruthenium, or a combination thereof, and may be platinum.

[0020] The organic ligand coordinating to the noble metal atom may be, for example, ammonia or an amine compound. The amine compound may be, for example, an alkylamine having 1 to 3 carbon atoms, an alkylenediamine having 1 to 3 carbon atoms (for example, ethylenediamine), a nitrogen-containing heteroaromatic compound (for example, 2,2'-bipyridine), or a cyclic diamine having an aliphatic heterocycle containing two nitrogen atoms coordinated to one noble metal atom. The alkylamine having 1 to 3 carbon atoms may be, for example, methylamine, ethylamine or n-propylamine.

[0021] The counter ion of the polyoxometalate compound is usually a cation since the metal-substituted polyoxometalate is an anion. The counter ion is not particularly limited, and may be, for example, Cs + , K + , Na + and Li + such metal cations, alkylammonium such as ammonium and tetramethylammonium, proton (H + ), or a combination thereof.

[0022] In the mixed solution, the carbon raw material may be dissolved in the hydrophilic solvent, or the solid carbon raw material (for example, nanofiber) may be dispersed in the hydrophilic solvent. The polyoxometalate compound is dissolved in the hydrophilic solvent. The hydrophilic solvent is selected from those in which the polyoxometalate compound is soluble. The hydrophilic solvent may be only water, or a mixed solvent containing water and other solvents (for example, alcohol). The proportion of water in the hydrophilic solvent may be 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more based on the amount of the hydrophilic solvent, and may be 100% by mass or less.

[0023] The concentration of the carbon raw material in the mixed solution may be, for example, 0.1% by mass or more and 50% by mass or less based on the mass of the mixed solution. The concentration of the polyoxometalate compound in the mixed solution may be, for example, 0.1% by mass or more and 50% by mass or less based on the mass of the mixed solution. The ratio of the mass of the polyoxometalate compound to the total mass of the carbon raw material and the polyoxometalate compound may be, for example, 1% by mass or more, 5% by mass or more, or 10% by mass or more, and may also be 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, or 50% by mass or less.

[0024] The mixed solution can be prepared, for example, by preparing a carbon raw material solution containing a carbon raw material and a hydrophilic solvent, in which the carbon raw material is dissolved or dispersed in the hydrophilic solvent, and dissolving a polyoxometalate compound in the hydrophilic solvent of the carbon raw material solution.

[0025] A solid mixture containing a carbon raw material and a polyoxometalate compound is taken out from the prepared mixed solution. By passing through the mixed solution in which the polyoxometalate compound is dissolved, a solid mixture in which the polyoxometalate compound is uniformly dispersed in the carbon raw material can be easily obtained. The solid mixture can be taken out by any method including removing the hydrophilic solvent. For example, the solid mixture can be obtained by a method including mixing the mixed solution with a poor solvent (e.g., t-butyl alcohol) of the polyoxometalate compound to precipitate a precipitate containing the carbon raw material and the polyoxometalate compound, and recovering the precipitate. The precipitate can be recovered by ordinary methods such as centrifugation, filtration, freeze drying, heat drying, and vacuum drying. The solid mixture may also be obtained by a method including distilling off the hydrophilic solvent from the mixed solution.

[0026] By firing the solid mixture, a noble metal-containing material is formed, which includes a carrier containing a carbonaceous material generated by carbonization of the carbon raw material and metal particles containing noble metal atoms. The metal particles are supported on the carrier containing the carbonaceous material.

[0027] The solid mixture is fired under conditions such that the carbon raw material is appropriately carbonized. The heating temperature for firing may be, for example, at most 800°C or higher and 1200°C or lower. From the viewpoint of the power generation performance of a fuel cell having an electrode catalyst layer containing a noble metal-containing material, the heating temperature for firing may be at most 850°C or higher, 900°C or higher, or 950°C or higher, and may be 1150°C or lower, or 1100°C or lower. The firing may include heating at a constant temperature or may include multi-stage heating in which two or more different temperatures are maintained. The time for which the solid mixture is heated for firing may be, for example, 30 minutes or longer and 10 hours or shorter. The time for which the solid mixture is heated at a temperature of 800°C or higher, 850°C or higher, 900°C or higher, or 950°C or higher may be 30 minutes or longer and 10 hours or shorter. The firing of the solid mixture may be performed in an inert gas atmosphere such as nitrogen gas.

[0028] The metal particles in the noble metal-containing material contain a noble metal (for example, platinum) derived from a polyoxometalate compound. When the particle size of the metal particles is small, high catalytic performance is likely to be exhibited. The particle size of the metal particles may be, for example, 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, or 50 nm or less, and may be 0.1 nm or more or 1 nm or more. The particle size here can be the maximum width of the metal particles observed in the transmission electron microscope image of the noble metal-containing material (the maximum value of the distance between two parallel straight lines sandwiching the image of the metal particles). The average value of the particle sizes of any 30 or more metal particles observed in the transmission electron microscope image may be within the above range. According to the method according to the present disclosure, a noble metal-containing material containing fine metal particles containing noble metal atoms can be easily formed.

[0029] The content of the metal particles (or noble metal) in the noble metal-containing material may be, for example, 5% by mass or more and 50% by mass or less based on the mass of the noble metal-containing material.

[0030] The carbonaceous material in the carrier is an arbitrary carbon material and can include, for example, amorphous carbon, graphite, or a combination thereof. The carbonaceous material may be conductive.

[0031] The carrier containing the carbonaceous material may further contain metal atoms derived from a polyoxometalate compound. The metal atoms in the carrier may be transition metal atoms (such as tungsten or molybdenum) derived from polyoxometalate. When the counter ion of the polyoxometalate compound is a metal cation, the metal atom (such as cesium) may be contained in the carrier. The metal atoms in the carrier may form an oxide. The inclusion of metal atoms in the carrier can be confirmed, for example, by energy dispersive X-ray spectroscopy (EDS).

[0032] The shape of the carrier is not particularly limited, and it may be fibrous. The fibrous carrier is advantageous, for example, in terms of the catalytic activity of the noble metal-containing material. When the carbon raw material is fibrous, a fibrous carrier is easily formed. The fiber diameter of the fibrous carrier may be, for example, 1 nm or more and 100 nm or less.

[0033] The noble metal-containing material can be used for any application that utilizes the catalytic activity of the noble metal, etc. The layer containing the noble metal-containing material is useful, for example, as an electrode catalyst layer (cathode catalyst layer or anode catalyst layer) of a fuel cell. The layer containing the noble metal-containing material may further contain a binder. The layer containing the noble metal-containing material and the binder can be formed, for example, by a method including preparing a dispersion containing particulate noble metal-containing material, binder, and dispersion medium, forming a film of the dispersion, and removing the dispersion medium from the film of the dispersion. The binder may be, for example, an ionomer resin. The dispersion medium may be, for example, water, alcohol, or a combination thereof. The proportion of the noble metal-containing material in the electrode catalyst layer may be, for example, 0.3 mass% or more and 90 mass% or less based on the mass of the electrode catalyst layer. The areal amount of noble metal atoms (the mass of noble metal atoms per 1 cm 2 of the electrode catalyst layer) may be, for example, 0.01 mg / cm 2 or more and 3 mg / cm 2 or less. The thickness of the electrode catalyst layer may be, for example, 5 μm or more and 100 μm or less.

[0034] The electrode catalyst layer may be incorporated into a fuel cell as a membrane electrode assembly (MEA). FIG. 2 is a cross-sectional view showing an example of the membrane electrode assembly. The membrane electrode assembly 1 shown in FIG. 2 includes an electrolyte membrane 10, a cathode catalyst layer 21, and an anode catalyst layer 22. The cathode catalyst layer 21 is disposed on one main surface side of the electrolyte membrane 10, and the anode catalyst layer 22 is disposed on the other main surface side of the electrolyte membrane 10. The cathode catalyst layer 21, the anode catalyst layer 22, or both of them can include the noble metal-containing material according to the present disclosure. In particular, the cathode catalyst layer may include the noble metal-containing material according to the present disclosure. The electrolyte membrane 10 may be a solid electrolyte membrane. The electrolyte membrane 10 may be a solid polymer electrolyte membrane containing a polymer electrolyte (for example, an ionomer resin).

Example

[0035] The present invention is not limited to the following examples.

[0036] 1. Carbon raw material As the carbon raw material, a chitosan nanofiber (ChNF) and a ChNF aqueous dispersion (BiNFi-s EFo-08002 (trade name), Sugino Machine Co., Ltd., chitosan nanofiber concentration: 2% by mass) containing water were prepared.

[0037] 2. Polyoxometalate compound containing noble metal atoms A polyoxometalate compound Cs having a Keggin-type polyoxometalate, two divalent platinum atoms introduced into the defect site, and a metal-substituted polyoxometalate having ammonia coordinated to the platinum atom, and a cesium cation. 3 [PW 11 O 39 {cis-Pt(NH 3 ) 2} 2 ·8H 2 O (hereinafter referred to as "Cs-P-Pt") was prepared.

[0038] 3. Noble metal-containing material To 40 g of the ChNF aqueous dispersion, 0.25 g of Cs-P-Pt was added, and the mixture was heated at 80 °C for 30 minutes to dissolve Cs-P-Pt in water. Subsequently, the mixture was stirred using a stirring and defoaming machine (Haimerja HM-200WD (trade name), Kyoritsu Seiki Co., Ltd.) to form a uniform mixture in which ChNF was dispersed and Cs-P-Pt was dissolved. In the mixture, the ratio of the mass of Cs-P-Pt to the total mass of ChNF and Cs-P-Pt was approximately 24% by mass. 10 g of the mixture was placed in a centrifuge tube with a capacity of 50 mL, and t-butyl alcohol was further added thereto so that the total volume became approximately 40 mL. By vigorously shaking the centrifuge tube, the mixture and t-butyl alcohol were uniformly mixed. The mixture in the centrifuge tube was separated into a precipitate and a supernatant by a centrifuge. The supernatant was removed, t-butyl alcohol was added so that the total volume became approximately 40 mL, and the mixture was separated again into a precipitate and a supernatant by a centrifuge. The supernatant was removed, and t-butyl alcohol was removed from the precipitate by freeze-drying to obtain a solid mixture (Cs-P-Pt / ChNF) containing ChNF and Cs-P-Pt.

[0039] The solid mixture was placed in an alumina crucible, and the alumina crucible was covered with a lid. The alumina crucible was placed in an alumina box provided with a hole for introducing nitrogen, and the box was covered with a lid. With an inlet tube for introducing nitrogen gas attached to the hole of the alumina box, the alumina box was placed in an electric furnace. While introducing nitrogen gas into the box at a flow rate of 2 NL / min through the inlet tube, the temperature inside the electric furnace was raised to 800 °C at a rate of 10 °C / min and held at 800 °C for 1 hour to bake the solid mixture (Cs-P-Pt / ChNF). Thereafter, when the temperature inside the electric furnace was lowered to 250 °C or lower at a rate of 10 °C / min, the alumina crucible was taken out, and a part of the noble metal-containing material (Cs-P-Pt / C-800), which is a fired body of the solid mixture, was recovered. Thereafter, the alumina crucible was returned into the electric furnace, and the temperature inside the electric furnace was raised to 1000 °C at a rate of 10 °C / min and further baked in the same procedure as above except that the holding temperature was changed to 1000 °C or 1200 °C. By this baking, a noble metal-containing material (Cs-P-Pt / C-800-1000) obtained by baking at 800 °C and 1000 °C, and a noble metal-containing material (Cs-P-Pt / C-800-1200) obtained by baking at 800 °C and 1200 °C were obtained. Figures 3(a) and (b) are transmission electron microscope images of the noble metal-containing material (Cs-P-Pt / C-800-1000). It was confirmed that nano-scale minute platinum particles were dispersed in a fibrous carrier containing a carbonaceous material with almost no aggregation.

[0040] The mass of the obtained noble metal-containing material was measured to determine the carbonization yield. Also, the platinum content of the noble metal-containing material was measured using an ICP emission spectroscopic analyzer (Avio 500, PerkinElmer Japan Co., Ltd.). These results are shown in Table 1.

[0041]

Table 1

[0042] 4. Fabrication and Evaluation of Fuel Cell (1) Cathode Catalyst Layer The noble metal-containing material (Cs-P-Pt / C-800-1000) was pulverized in a mortar, and the particulate pulverized product was mixed with a dispersion of an ionomer resin (Nafion (registered trademark)) (DE520 (trade name), manufactured by Fujifilm Wako Pure Chemical Corporation), and a mixed solution of isopropyl alcohol:ion-exchanged water = 1:1 (mass ratio) was added thereto as a dispersion medium. The charged amount was adjusted so that the mass ratio of the carbonaceous material (carbon) contained in the noble metal-containing material to the ionomer resin was 1:1. The formed dispersion was stirred using a stirring and defoaming machine (Hi-merger HM-200WD (trade name), manufactured by Kyoritsu Seiki Co., Ltd.) to form a uniform coating solution. The coating solution was dropped onto a fluororesin sheet (MSF-100 (trade name), manufactured by Chukyo Kasei Kogyo Co., Ltd.) with a thickness of 100 μm fixed to a vacuum chuck and uniformly spread with an applicator to form a coating film with a thickness of about 100 μm. The coating film was dried at 100 °C to form a cathode catalyst layer containing the noble metal-containing material and the ionomer resin.

[0043] A 1.5 cm square laminate was punched out from the cathode catalyst layer and the fluororesin sheet and used for MEA production. From the mass of only the portion of the fluororesin sheet punched out near the location where the laminate was punched out and the mass difference of the laminate, and from the mixing ratio in the coating solution, the platinum coating amount (mg / cm 2 , per 1 cm 2 of the cathode catalyst layer) of platinum was calculated. The platinum coating amount was 0.036 mg / cm 2 .

[0044] (2) Anode catalyst layer An anode catalyst layer was formed on a fluororesin sheet in the same manner as the cathode catalyst layer, except that a commercially available platinum-supported carbon material (Pt / C) was used. A 1.5 cm square laminate punched out from the anode catalyst layer and the fluororesin sheet was used for MEA production.

[0045] (3) Membrane electrode assembly (MEA) As a solid electrolyte membrane, a membrane containing an ionomer resin (Nafion (registered trademark) membrane, NR211 (trade name), Chemix Co., Ltd.) was prepared. A laminate of a cathode catalyst layer and a fluororesin sheet and a laminate of an anode catalyst layer and a fluororesin sheet were arranged with the solid polymer electrolyte membrane interposed therebetween so that the cathode catalyst layer and the anode catalyst layer faced each other. A 1 cm square aluminum spacer was placed at the center of a laminate having a structure of fluororesin sheet / cathode catalyst layer / solid polymer electrolyte membrane / anode catalyst layer / fluororesin sheet, and the whole was further sandwiched between two aluminum plates. From the outside of the two aluminum plates, a compression load of 50 kgf was applied for 3 minutes while heating to 140 °C with a hot press machine. As a result, about 1 cm 2 square of the cathode catalyst layer and the anode catalyst layer were transferred from the fluororesin sheet onto the solid polymer electrolyte membrane, and an MEA of an example composed of a cathode catalyst layer (Cs-P-Pt / C-800-1000), a solid polymer electrolyte membrane, and an anode catalyst layer (Pt / C) was formed.

[0046] An MEA of a reference example composed of a cathode catalyst layer (Pt / C), a solid polymer electrolyte membrane, and an anode catalyst layer (Pt / C) was prepared by the same procedure as above except that a catalyst layer formed using a commercially available platinum-supported carbon material (Pt / C) as the cathode catalyst layer was used.

[0047] (4) Fuel cell Using the prepared MEA of the example or the reference example, a serpentine flow path type separator having five flow paths (EX-2C (trade name), Eiwa Co., Ltd.), a gasket (a fluororesin sheet with a thickness of 180 μm, MSF-100 (trade name), Chukyo Kasei Kogyo Co., Ltd.), and a gas diffusion layer (carbon paper, GDL28BC (trade name), SGL Carbon Japan Co., Ltd.), a fuel cell having the configuration of a JARI standard cell (EX-1N, Eiwa Co., Ltd.) was assembled.

[0048] (5) Evaluation Initial power generation performance The initial power generation performance of the assembled fuel cell was evaluated using a fuel cell evaluation system (PEMTest8900, Toyo Technica Co., Ltd.) and an electrochemical measurement system (HZ-7000, Hokuto Denko Corporation). As pre-measurement aging, the fuel cell was held for 3 hours under the conditions of a humidification temperature of 80°C, a cell temperature of 80°C, a supply rate of anode gas (H 2 ) of 200 NmL / min, a supply rate of cathode gas (air) of 200 NmL / min, and a voltage of 0.2 V. Thereafter, the conditions were set so that the gas utilization rate was 2% (minimum flow rate: 200 mL / min) for both the anode and the cathode, and I-V measurement was performed in the range of 0 to 2 A. FIG. 4 is an I-V curve showing the relationship between voltage and current density in a fuel cell having the MEA of the example or the reference example. The fuel cell having the MEA of the example showed power generation performance similar to that of the fuel cell having the MEA of the reference example.

[0049] After the I-V measurement, the flow rate of the anode gas (H 2 ) was changed to 70 mL / min, and the cathode gas was changed to N 2 , and its flow rate was changed in the order of 1000 NmL / min for 10 minutes, 166 NmL / min for 10 minutes, and 0 NmL / min. At this point, cyclic voltammetry (CV) measurement was performed 5 times in the range of 0.05 V to 0.9 V at a sweep rate of 50 mV / s. From the measurement data of the 5th time, the amount of electricity Q + (μC) due to the cathode current (current associated with the adsorption of H 1 on the platinum surface) from 0.4 V to 0.1 V was obtained. The electrochemical surface area (ECSA) of platinum in the cathode catalyst layer was calculated by the following formula. ECSA (m 2 / g -Pt) = Q 1 / (Q 0 ·W Pt )

[0050] In the formula, Q 0 is the adsorption charge amount of H 2 per 1 cm + of the platinum surface area, and its value was set to 210 μC / cm 2 -Pt. W Ptis the platinum coating weight in the cathode catalyst layer, and its value is 0.036 mg / cm in the case of Cs-P-Pt / C-800-1000. 2 It was.

[0051] Durability The supply rate of the anode gas (H 2 ) was set to 70 NmL / min, and the supply rate of the cathode gas (N 2 ) was set to 166 NmL / min. A process in which a voltage of 1.0 V for 3 seconds and then 0.6 V for 3 seconds was applied to the fuel cell was defined as one load response cycle, and this process was repeated. When 500, 1000, 2000, 3000, 4000, 6000, 8000, or 10000 load response cycles were completed, CV measurement was performed under the same conditions as the initial power generation performance to obtain the ECSA. FIG. 5 is a graph showing the relationship between the ECSA and the number of load response cycles for a fuel cell having the MEA of the example or the reference example. It was confirmed that the fuel cell of the example exhibited durability comparable to that of the fuel cell of the reference example using a normal platinum-supported carbon material.

Description of symbols

[0052] 1... Membrane electrode assembly, 10... Electrolyte membrane, 21... Cathode catalyst layer, 22... Anode catalyst layer.

Claims

1. Preparing a mixed solution containing a carbon raw material, a polyoxometalate compound containing noble metal atoms, and a hydrophilic solvent containing water, wherein the carbon raw material is dissolved or dispersed in the hydrophilic solvent and the polyoxometalate compound is dissolved in the hydrophilic solvent; Taking out a solid mixture containing the carbon raw material and the polyoxometalate compound from the mixed solution; Forming a noble metal-containing material by firing the solid mixture, the noble metal-containing material including a carrier containing a carbonaceous material generated by carbonization of the carbon raw material and metal particles containing the noble metal atoms supported on the carrier; comprising; The polyoxometalate compound has a metal-substituted polyoxometalate and its counter ion; The metal-substituted polyoxometalate has a polyoxometalate having one or more defect sites and the noble metal atoms introduced into the defect sites; A method for producing a noble metal-containing material.

2. The method according to claim 1, wherein the carbon raw material includes an organic compound containing nitrogen atoms.

3. The method according to claim 1, wherein the carbon raw material includes nanofibers having a fiber diameter of less than 1 μm, microfibers having a fiber diameter of 1 μm or more and less than 1 mm, or a combination thereof.

4. The method according to claim 3, wherein the carbon raw material includes the nanofibers, and the nanofibers include chitosan nanofibers, chitin nanofibers, or a combination thereof.

5. The method according to claim 1, wherein the noble metal atoms include platinum, palladium, ruthenium, or a combination thereof.

6. Preparing a noble metal-containing material including a carrier containing a carbonaceous material and metal particles containing noble metal atoms by the method according to claim 1; Forming an electrode catalyst layer containing the noble metal-containing material; A method for producing an electrode catalyst layer, comprising.

7. A noble metal-containing material including a carrier containing a carbonaceous material and transition metal atoms; Metal particles containing noble metal atoms supported on the carrier; comprising.

8. The noble metal-containing material according to claim 7, which is fibrous.

9. The noble metal-containing material according to claim 7, wherein the particle size of the metal particles is 100 nm or less.

10. Comprising an electrolyte membrane and an electrode catalyst layer disposed on the electrolyte membrane; The electrode catalyst layer contains the noble metal-containing material according to claim 7; A membrane electrode assembly for a fuel cell.

11. A fuel cell comprising the membrane electrode assembly for a fuel cell according to claim 10.

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