Electrode catalyst for fuel cell

Abstract

To provide a new electrode catalyst for a fuel cell capable of exhibiting high activity at low cost.SOLUTION: The electrode catalyst for fuel cells according to an exemplary embodiment is an electrode catalyst for fuel cells comprising a carbon material, wherein the carbon material is a nitrogen-containing carbon material obtained by carbonization of 1, 7-phenanthroline.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrode catalyst for a fuel cell. [Background technology]

[0002] Fuel cells have been attracting attention as a power generation system that can achieve high energy conversion efficiency and reduce environmental impact. Fuel cells use electrical energy obtained through the electrochemical reaction between hydrogen and oxygen as power.

[0003] Solid polymer fuel cells, a typical type of fuel cell, generally use an electrode catalyst in which platinum is supported on a carbon material. However, platinum is an expensive rare metal. Therefore, in order to popularize fuel cells, it is necessary to reduce the cost of fuel cell electrode catalysts.

[0004] As platinum-free fuel cell catalysts, a fuel cell catalyst obtained by supporting a coordination polymer metal complex on a carbon-based support and calcining the catalyst (Patent Document 1) and a fuel cell catalyst obtained by supporting a conductive polymer on a carbon support and calcining the catalyst (Patent Document 2) have been reported. However, these have not yet reached a level where they can be widely used as electrode catalysts for fuel cells.

[0005] Recently, it has been reported that nitrogen-containing carbon materials containing carbon atoms, nitrogen atoms, and halogen atoms may be applicable to electrodes of fuel cells (Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-243161 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-232409 [Patent Document 3] Japanese Patent Application Publication No. 2023-77225 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a novel electrode catalyst for fuel cells that can exhibit high activity at low cost. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to develop a novel fuel cell electrode catalyst that can exhibit high activity at low cost. As a result, they have found that a fuel cell electrode catalyst using a carbon material obtained from a specific nitrogen-containing heterocyclic compound can exhibit high activity, and have completed the present invention.

[0009] [1] An electrode catalyst for a fuel cell according to an embodiment of the present invention is an electrode catalyst for a fuel cell containing a carbon material, wherein the carbon material is a nitrogen-containing carbon material obtained by carbonization of 1,7-phenanthroline. [2] In the fuel cell electrode catalyst according to the above item [1], the carbon material may be supported on a carbon material support other than the carbon material. [3] In the fuel cell electrode catalyst according to the above [2], the carbon material support may be at least one selected from the group consisting of carbon black, carbon nanotubes, activated carbon, and graphene. [Effects of the Invention]

[0010] According to the present invention, a novel, highly active electrode catalyst for a fuel cell can be provided. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing the results of oxygen reduction performance evaluation of fuel cell electrode catalysts obtained in Examples and Comparative Examples. [Figure 2] FIG. 10 is another diagram showing the results of the oxygen reduction performance evaluation of the fuel cell electrode catalysts obtained in the examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0012] ≪Electrode catalyst for fuel cells≫ The fuel cell electrode catalyst according to the embodiment of the present invention contains a carbon material. The carbon material may be one type or two or more types. In this specification, the carbon material contained in the fuel cell electrode catalyst according to the embodiment of the present invention may be referred to as carbon material (A).

[0013] In the fuel cell electrode catalyst according to the embodiment of the present invention, the carbon material (A) may be supported on a carbon material support other than the carbon material (A).

[0014] As the carbon material support, any appropriate carbon material support other than the carbon material (A) can be used as long as it does not impair the effects of the present invention. Such a carbon material support may be one type or two or more types. In terms of being able to produce a highly active fuel cell electrode catalyst, such a carbon material support is preferably at least one type selected from the group consisting of carbon black, carbon nanotubes, activated carbon, and graphene.

[0015] In the fuel cell electrode catalyst according to the embodiment of the present invention, when the carbon material (A) is supported on a carbon material support other than the carbon material (A), the weight of the carbon material (A) depends on the specific surface area of ​​the support. 2 / g~140m 2 In the case of a carbon material carrier having a carbon content of 0.01 to 50 parts by weight, more preferably 0.1 to 25 parts by weight, even more preferably 0.5 to 10 parts by weight, and particularly preferably 1 to 5 parts by weight, relative to 100 parts by weight of the carbon material (A). The thickness of the carbon material (A) on the carrier is preferably in the range of 0.1 to 5 layers, calculated as a graphene-like substance.

[0016] The carbon material (A) is a nitrogen-containing carbon material obtained by carbonizing 1,7-phenanthroline, which is represented by the chemical formula (1). [ka]

[0017] The carbon material (A) contains carbon atoms and nitrogen atoms.

[0018] Patent Document 3 describes a carbon material obtained by carbonizing a nitrogen-containing aromatic compound containing at least 1,10-phenanthroline containing a halogen atom as a substituent (paragraph

[0038] , etc.), and in the examples, a carbon material is synthesized by carbonizing 1,10-phenanthroline containing a halogen atom as a substituent. Patent Document 3 also describes the possibility of applying such a carbon material as an electrode for a fuel cell (paragraph

[0011] , etc.). However, Patent Document 3 states that the nitrogen-containing aromatic compound used as a raw material for the carbon material contains a halogen atom, which may cause environmental problems. Furthermore, Patent Document 3 does not evaluate the actual application of the obtained carbon material as an electrode for a fuel cell.

[0019] In the present invention, carbon material (A) is supported on a carbon material support other than carbon material (A) using as a raw material 1,7-phenanthroline, which does not contain halogen atoms as substituents and has a nitrogen atom at a different position from that of the 1,10-phenanthroline, and it has been found that the carbon material is useful as a highly active electrode catalyst for fuel cells.

[0020] In a material obtained by supporting a carbon material (A) on a carbon material support other than the carbon material (A) using 1,7-phenanthroline as a raw material, the total carbon atom content of the carbon material (A) alone, excluding the carbon material support, is preferably 50 at% or more, more preferably 60 at% or more, even more preferably 65 at% or more, and particularly preferably 70 at% or more. The upper limit of the total carbon atom content is preferably 99 at% or less, more preferably 95 at% or less. The total carbon atom content in the carbon material (A) is calculated from the elemental analysis values ​​of the carbon material (A) alone, excluding the carbon material support. Specifically, the elemental analysis values ​​of each constituent element are divided by the atomic weight to calculate the composition ratio of the carbon material (A), and the total carbon atom content (at%) can be calculated based on the obtained composition ratio.

[0021] In a material obtained by supporting a carbon material (A) on a carbon material support other than the carbon material (A) using 1,7-phenanthroline as a raw material, the total content of nitrogen atoms in the components of the carbon material (A) alone, excluding the carbon material support, is preferably 1 at% or more, more preferably 2 at% or more, even more preferably 3 at% or more, and particularly preferably 5 at% or more. The upper limit of the total content of nitrogen atoms is preferably 20 at% or less, more preferably 18 at% or less. The total content of nitrogen atoms in the carbon material (A) is calculated from the elemental analysis values ​​of the components of the carbon material (A) alone, excluding the carbon material support. Specifically, the elemental analysis values ​​of each constituent element are divided by the atomic weight to calculate the composition ratio of the carbon material (A), and the total content (at%) of nitrogen atoms can be calculated based on the obtained composition ratio.

[0022] The carbon material (A) may be a nitrogen-containing carbon material containing a pyridinic nitrogen atom or a tertiary nitrogen atom. Nitrogen-containing carbon materials containing a pyridinic nitrogen atom or a tertiary nitrogen atom may have electrocatalytic activity for redox reactions and therefore may be suitable for use as an electrocatalyst for fuel cells. The term "pyridinic nitrogen atom" refers to a secondary nitrogen atom in which one secondary nitrogen atom is located within a six-membered ring structure, giving the structure similar to a benzene ring. The term "tertiary nitrogen atom" refers to a nitrogen atom bonded to three carbon atoms.

[0023] In the carbon material (A), the ratio of the number of moles of pyridinic nitrogen atoms and tertiary nitrogen atoms to the total number of moles of nitrogen atoms is preferably 50% or more, more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more. The ratio of the number of moles of pyridinic nitrogen atoms and tertiary nitrogen atoms to the total number of moles of nitrogen atoms can be analyzed, for example, by measuring the XPS spectrum of the nitrogen 1s orbital by XPS.

[0024] Carbon material (A) exhibits a G band (1570 cm) in Raman spectroscopy. -1 More than 1600cm -1 below range), D band (1300 cm -1 More than 1400cm -1 The G band is generally a band associated with a graphene structure or a chemical structure similar to the graphene structure. The D band is a band that reflects the presence of structural defects or functional groups contained in a graphene structure or a chemical structure similar to the graphene structure. In Raman spectroscopy, the carbon material (A) exhibits a D' band (1600 cm -1 More than 1650cm -1 below range), 2D band (2650 cm -1 More than 2750cm -1 below range), D+G band (2800cm -1 More than 3000cm -1 below range), and 2G band (3100cm -1 More than 3300cm -1 The positions of the above bands in this specification are those observed when the wavelength of the excitation light source is 532 nm.

[0025] The carbon material (A) is obtained by carbonizing 1,7-phenanthroline. In one embodiment, the carbonization of 1,7-phenanthroline can be carried out by heat-treating 1,7-phenanthroline. In order to obtain a highly active electrode catalyst for a fuel cell, the temperature for the heat treatment of 1,7-phenanthroline is preferably 620°C to 1400°C, more preferably 640°C to 1200°C, even more preferably 660°C to 1100°C, and particularly preferably 680°C to 1000°C.

[0026] In an embodiment of the present invention, the heat treatment of 1,7-phenanthroline may be carried out in the presence of a carbon material support other than the carbon material (A) to be obtained, thereby obtaining the carbon material (A) in a state in which the carbon material (A) is supported on a carbon material support other than the carbon material (A).

[0027] As explained above, the carbon material support is preferably at least one selected from the group consisting of carbon black, carbon nanotubes, activated carbon, and graphene, which can be used to produce a highly active fuel cell electrode catalyst. Graphene also includes graphene oxide, which is obtained by oxidizing and exfoliating graphite.

[0028] When the heat treatment of 1,7-phenanthroline is carried out in the presence of a carbon material support other than the resulting carbon material (A), a highly active electrode catalyst for a fuel cell can be obtained. Therefore, the amount of the carbon material support used relative to 1,7-phenanthroline is preferably 100 to 10,000 parts by weight, more preferably 500 to 8,000 parts by weight, even more preferably 1,000 to 6,000 parts by weight, and particularly preferably 1,500 to 4,000 parts by weight, per 100 parts by weight of 1,7-phenanthroline.

[0029] <Method for manufacturing fuel cell electrode catalyst> The fuel cell electrode catalyst according to the embodiment of the present invention can be typically produced by heat treating 1,7-phenanthroline in the presence of a carbon material support.

[0030] The carbon material support is a carbon material support other than the carbon material (A) obtained by carbonization of 1,7-phenanthroline. Such a carbon material support may be one type only or two or more types. In terms of being able to become a highly active fuel cell electrode catalyst, such a carbon material support is preferably at least one type selected from the group consisting of carbon black, carbon nanotubes, activated carbon, and graphene.

[0031] In order to obtain a highly active electrode catalyst for a fuel cell, the temperature for the heat treatment is preferably 620°C to 1400°C, more preferably 640°C to 1200°C, even more preferably 660°C to 1100°C, and particularly preferably 680°C to 1000°C.

[0032] The heat treatment may be carried out under sealed tube conditions. By carrying out the heat treatment under sealed tube conditions, for example, sublimation of 1,7-phenanthroline can be suppressed.

[0033] The heat treatment may be carried out under reduced pressure or in vacuum. By carrying out the heat treatment under reduced pressure or in vacuum, for example, side reactions due to gases generated during carbonization can be suppressed.

[0034] After the heat treatment, the product may be crushed or purified. [Example]

[0035] The present invention will be specifically described below using examples, but the present invention is not limited to these examples. The test and evaluation methods used in the examples are as follows. The term "parts" means "parts by weight" unless otherwise specified, and the term "%" means "% by weight" unless otherwise specified.

[0036] [Example 1] 95 mg of carbon black (Denka Black Li Li-100) was placed in a glass tube and vacuum dried at 150°C for 1 hour. 5 mg of 1,7-phenanthroline was added in a glove box under a nitrogen atmosphere, and vacuum dried at 40°C for 1 hour. The glass tube was then sealed, placed in an electric furnace, and baked at 600°C (873K) for 1 hour. After baking, the tube was vacuum dried at 140°C for 1 hour to remove unreacted materials, yielding a fuel cell electrode catalyst (1).

[0037] [Example 2] The same procedure as in Example 1 was carried out except that the calcination temperature was changed from 600°C (873K) to 800°C (1073K), to obtain an electrode catalyst (2) for a fuel cell.

[0038] [Example 3] An electrode catalyst (3) for a fuel cell was obtained in the same manner as in Example 1, except that the calcination temperature was changed from 600°C (873K) to 1000°C (1273K).

[0039] [Comparative Example 1] 95 mg of carbon black (Denka Black Li Li-100) was placed in a glass tube and vacuum dried at 150°C for 1 hour. 5 mg of 1,10-phenanthroline was added in a glove box under a nitrogen atmosphere, and vacuum dried at 60°C for 1 hour. The glass tube was then sealed, placed in an electric furnace, and baked at 600°C (873K) for 1 hour. After baking, the tube was vacuum dried at 160°C for 1 hour to remove unreacted materials, yielding a fuel cell electrode catalyst (C1).

[0040] Comparative Example 2 An electrode catalyst for a fuel cell (C2) was obtained in the same manner as in Comparative Example 1, except that the calcination temperature was changed from 600°C (873K) to 1000°C (1273K).

[0041] Comparative Example 3 10 mg of carbon black (Denka Black Li Li-100) and 5 mg of 1,10-phenanthroline were mixed with 10 mL of methanol and sonicated for 1 hour. These two mixtures were then mixed and sonicated for another hour. The resulting mixture was heated at 80°C in air for 12 hours while stirring to remove the methanol, yielding a fuel cell electrode catalyst (C3).

[0042] <Oxygen reduction performance evaluation> Using a Metrohm Autolab rotating disk electrode evaluation device (model: PGSTAT302N), three electrodes (reversible hydrogen electrode: RHE, counter electrode: Pt, working electrode) were used in 0.1 M sulfuric acid saturated with oxygen. The fuel cell electrode catalyst was applied to the working electrode (application amount: 20 μL) and oxygen reduction performance was evaluated under the following conditions. Higher oxygen reduction performance indicates higher activity as a fuel cell electrode catalyst. Working electrode area: 0.28 cm 2 Rotation speed: 900 rpm Potential: 1.5V (vs RHE) Scan rate: 1.5mVs -1 The measurement results are shown in Figures 1 and 2. The abbreviations in Figures 1 and 2 refer to the following Examples and Comparative Examples. 1,7Phen / CB100_873: Fuel cell electrode catalyst (1) obtained in Example 1 1,7Phen / CB100_1073: Fuel cell electrode catalyst (2) obtained in Example 2 1,7Phen / CB100_1273: Fuel cell electrode catalyst (3) obtained in Example 3 1,10Phen / CB100_873: Fuel cell electrode catalyst (C1) obtained in Comparative Example 1 1,10Phen / CB100_1273: Fuel cell electrode catalyst (C2) obtained in Comparative Example 2 1,10Phen / CB100: Fuel cell electrode catalyst (C3) obtained in Comparative Example 3 [Industrial Applicability]

[0043] The fuel cell electrode catalyst according to the embodiment of the present invention can be suitably used in fuel cells, which are attracting attention as power generation systems that can achieve high energy conversion efficiency and reduce environmental impact.

Claims

1. An electrode catalyst for a fuel cell comprising a carbon material, the carbon material is a nitrogen-containing carbon material obtained by carbonization of 1,7-phenanthroline; Electrode catalyst for fuel cells.

2. 2. The fuel cell electrode catalyst according to claim 1, wherein the carbon material is supported on a carbon material support other than the carbon material.

3. 3. The fuel cell electrode catalyst according to claim 2, wherein the carbon material support is at least one selected from the group consisting of carbon black, carbon nanotubes, activated carbon, and graphene.

Images