WO2007145147A1

WO2007145147A1 - Method for producing iron-containing carbon material

Info

Publication number: WO2007145147A1
Application number: PCT/JP2007/061661
Authority: WO
Inventors: Jun Maruyama; Ikuo Abe; Junji Okamura; Kuninori Miyazaki
Original assignee: Nippon Shokubai Co., Ltd.
Priority date: 2006-06-16
Filing date: 2007-06-08
Publication date: 2007-12-21
Also published as: JP2008021638A; JP5143469B2

Abstract

Disclosed is a method for easily producing a low-cost carbon material having high catalytic activity which can be used in place of a platinum carbon material, or enables to significantly reduce the amount of platinum conventionally used in electrode catalyst material for solid polymer electrolyte fuel cells. Also disclosed are an oxygen reduction electrode containing an iron-containing carbon material produced by the method, and a solid polymer fuel cell having such an oxygen reduction electrode. Specifically disclosed is a method for producing an iron-containing carbon material, which comprises a step for mixing an iron salt, a nitrogen-containing compound and a carbohydrate, and a step for heat-treating the mixture in an inert atmosphere.

Description

Specification

Method for producing iron-containing carbon material

Technical field

The present invention relates to a method for producing a carbon material containing iron, and an oxygen reduction electrode and a solidified polymer fuel cell comprising the iron-containing carbon material as constituent components. Background art

[0002] Fuel cells are attracting attention as highly efficient power generation systems that are in harmony with the environment. In particular, solid polymer electrolyte fuel cells that use a fluorinated ion exchange membrane as the electrolyte can operate at normal temperatures and have a high output density. It is expected to be used widely as a system power supply.

[0003] For the practical use and widespread use of such fuel cells, cost reduction has become a major issue. Existing solid polymer electrolyte fuel cells generally contain expensive white metal as a component of the electrode catalyst. Therefore, a device for reducing the amount of platinum used is required for cost reduction. In addition, platinum reserves and production volumes are limited, and it is expected that the price of platinum will rise in the future when it spreads widely. Therefore, it is also necessary to develop inexpensive electrocatalyst materials that do not use platinum. It has become a problem.

[0004] One promising positive electrode catalyst material that does not use platinum is a catalyst that uses resource-rich iron. This catalyst has a structure in which iron atoms are bonded on the surface of a carbon material through nitrogen atoms, and this part functions as an active point of the catalyst.

[0005] The present inventors have developed a method for heat-treating an iron-containing natural compound such as power talase or hemoglobin in an inert atmosphere as a method for producing an iron-containing carbon material having such a catalytic action. (Japanese Unexamined Patent Application Publication No. 2004-217507). In addition, A. van der Putten et al., J. Electroanal. Chem., 205, pp. 233-244 (1986). Also, phthalocyanines or dibenzotetraazanulenes containing iron and kononoret are not used. A method of thermal decomposition in an active atmosphere is described. However, for these natural products containing iron, a large-scale acquisition route that is considered necessary for the spread of fuel cells has not been established yet. [0006] In addition, S. Gupta et al., J. Appl. Electrochem., 19, pp. 19-27 (1989) include polyacrylonitrile and cobalt salts or iron salts, and carbon materials for heat treatment of large surface area carbon. A manufacturing method is disclosed. G. Lalande et al., Electrochim. Acta, 42, pp. 1379-1388 (1987) (Polymer containing iron, ninoleferrocene, etc. are supported on carbon black and thermally decomposed in acetonitrile vapor. In addition, M. Lefevre et al., J. Phys. Chem. B 106, Nos. 8705-8713 (2002) describe the pyrolysis of perylenetetracarboxylic anhydride. However, it is disclosed that carbon materials obtained by the above method are loaded with iron acetate or iron-porphyrin and thermally decomposed, but in these methods, a special carbon material must be prepared in advance. It takes cost and effort S.

Disclosure of the invention

[0007] As described above, conventionally, carbon materials that contain iron instead of expensive platinum have been known as carbon materials that can be used as a catalyst for an oxygen reduction electrode of a solid polymer electrolyte fuel cell. . However, conventional iron-containing carbon materials cannot be easily and inexpensively manufactured because they use natural organic compounds as materials, or require special carbon materials to be prepared in advance.

Accordingly, the problem to be solved by the present invention is that the amount of platinum conventionally used as an electrode catalyst material for a solid polymer electrolyte fuel cell can be remarkably reduced, or can be used in place of a platinum carbon material. Therefore, an object of the present invention is to provide a method for easily producing an inexpensive carbon material having high catalytic activity. Another object of the present invention is to provide an oxygen reduction electrode containing the iron-containing carbon material produced by the method, and a polymer electrolyte fuel cell having the oxygen reduction electrode.

[0009] The present inventors have intensively studied to solve the above problems. As a result, the inventors have found that if a material to be used is devised, a carbon material having a high catalytic action can be produced without using an expensive material such as a natural organic compound or a special carbon material, and the present invention has been completed.

[0010] The method for producing an iron-containing carbon material according to the present invention includes a step of mixing an iron salt, a nitrogen-containing compound and a carbohydrate, and a step of heat-treating the mixture in an inert atmosphere. To do. [0011] The iron-containing carbon material of the present invention is manufactured by the above-described method of the present invention. Further, the oxygen reduction electrode of the present invention is characterized by including an iron-containing carbon material produced by the above method, and the solidified polymer fuel cell of the present invention has the oxygen reduction electrode. .

Brief Description of Drawings

[0012] FIG. 1 is a graph showing the relationship between current I and electrode potential E, which is an index of oxygen reduction activity of the electrode catalyst layers formed in Examples 1, 2, 3 and Comparative Example 1.

K

FIG. 2 is a diagram showing the relationship between current I and electrode potential E, which are indicators of the oxygen reduction activity of the electrode catalyst layers formed in Examples 4 and 5 and Comparative Example 2.

K

BEST MODE FOR CARRYING OUT THE INVENTION

[0013] A method for producing an iron-containing carbon material according to the present invention includes a step of mixing an iron salt, a nitrogen-containing compound and a carbohydrate, and a step of heat-treating the mixture in an inert atmosphere. To do. Hereinafter, according to the order of implementation, the method of the present invention will be described.

[0014] The iron salt used as a raw material in the method of the present invention is important as a supply source of iron that exhibits a catalytic action instead of platinum in the carbon material according to the present invention. The type is not particularly limited, and either a divalent iron salt or a trivalent iron salt can be used. For example, iron halides such as iron fluoride, iron chloride, iron bromide, iron iodide, and the like; iron such as iron nitrate, iron sulfate, iron phosphate, etc. An inorganic acid salt of iron; an organic acid salt of iron such as iron acetate, iron citrate, iron dalconate, iron oxalate, and iron lactate can be used. In addition, one type of iron salt may be selected and used, or two or more types may be mixed and used. Preferably, iron lactate (I I) or iron (II) dulconate is used.

[0015] In addition to the iron salt, other inexpensive metal salts may be used. There is a possibility that the catalytic performance of carbon materials can be improved by further adding inexpensive metal salts other than iron salts. Such metal salts include, for example, halides of copper, nickel, cobalt, chromium, manganese, and vanadium, such as fluorides, chlorides, bromides, iodides; nitrates, sulfates, phosphates, etc. Inorganic acid salts; organic acid salts such as acetates, citrates, dalconates, oxalates, and lactates.

[0016] The nitrogen-containing compound used in the present invention captures iron in the carbon material according to the present invention. It is important as a supply of nitrogen atoms. The type of nitrogen-containing compound that can be used is not particularly limited, but the present invention aims to produce an iron-containing carbon material inexpensively and easily, and therefore, purification and cost such as protein are laborious. It is preferable not to use a compound that is originally expensive. Examples of nitrogen-containing compounds include amino acids; purine bases such as adenine and guanine; and pyrimidin bases such as uracil, thymine, and cytosine.

[0017] Carbohydrates used in the present invention have a role of sufficiently supplying carbon that tends to be deficient with only nitrogen-containing compounds. Carbohydrate is sometimes used as an alternative name for sugar, but in the present invention, the term carbohydrate is used to exclude nitrogen-containing amino sugars such as darcosamine from the range and distinguish them from nitrogen-containing compounds. Therefore, in general, the carbohydrate may be interpreted as including an amino sugar, but the carbohydrate of the present invention is composed of a carbon atom, a hydrogen atom, and an oxygen atom. However, the carbohydrates of the present invention are not limited to those represented by the general formula: (CH0), and sugar alcohols not represented by (CH0)

2 n 2 n

It also includes the rules. Examples of strong carbohydrates include monosaccharides such as fructose and gnoleose; oligosaccharides such as sucrose, maltose, and ratatose; sugar alcohols such as sorbitol and xylitol; and sugar acids such as glucuronic acid. Among these, glucose is preferable because it is inexpensive.

[0018] The amount of the nitrogen-containing compound used is usually preferably 1 part by mass or more and 1000 parts by mass or less with respect to 100 parts by mass of the carbohydrate. If the amount of the nitrogen-containing compound is 1 part by mass or more with respect to 100 parts by mass of carbohydrates, the ratio of nitrogen atoms in the carbon material is sufficient, and a sufficient amount of iron can be bound. If so, the amount of nitrogen atoms in the carbon material will not be excessive. A more preferable use amount of the nitrogen-containing compound is 10 parts by mass or more and 500 parts by mass or less with respect to 100 parts by mass of the carbohydrate.

[0019] The amount of the iron salt used or the total amount of the iron salt and other metal salt is usually 0.01 parts by mass or more and 100 parts by mass with respect to 100 parts by mass of the total of the nitrogen-containing compound and the carbohydrate. Part or less. When the iron salt amount is 0.01 parts by mass or more with respect to 100 parts by mass of the total of the nitrogen-containing compound and the carbohydrate, the carbon material according to the present invention exhibits a catalytic action. The amount of iron can be secured sufficiently, and if it is 100 parts by mass or less, the amount of iron in the carbon material is not considered to be a square IJ. A more preferable amount of the iron salt used is 0.1 parts by mass or more and 10 parts by mass or less based on 100 parts by mass of the total of the nitrogen-containing compound and the carbonate.

[0020] The iron salt, nitrogen-containing compound and carbohydrate to be used are preferably pulverized before or after mixing. This is because each component is finer and heat treatment efficiency is higher.

[0021] After mixing the iron salt, nitrogen-containing compound and carbohydrate, the mixture is heat-treated in an inert atmosphere. An inert atmosphere refers to an atmosphere that does not contain oxygen in such an amount that carbon in the raw material is oxidized. The inert atmosphere is not particularly limited, and examples thereof include the following atmospheres (i) to (v):

(i) an inert atmosphere comprising an inert gas such as argon or nitrogen,

(ii) a reducing atmosphere comprising a reducing gas such as hydrogen;

(iii) An atmosphere generally used for activation treatment of activated carbon, in which water vapor or carbon dioxide is added to an inert gas such as nitrogen or argon,

(iv) An atmosphere other than the above (iii) that is generally used for activation treatment of activated carbon, wherein the amount of oxygen is limited to such an extent that organic natural products are not burned,

(V) —The atmosphere during general steaming.

[0022] The inert gas and the reducing gas may be used alone or in combination of two or more as the inert atmosphere. In particular, when the heat treatment is performed in the above atmosphere (iii) or (iv), an activation effect is also obtained, so that a carbon material having a larger specific surface area than that obtained by heat treatment in another atmosphere can be obtained.

[0023] The heat treatment temperature is not particularly limited, but is usually about 400 to 1500 ° C, preferably about 600 to 1000 ° C. If the heat treatment temperature is too low, the carbon structure is undeveloped and the electrical conductivity required as an electrode catalyst is low, and if the heat treatment temperature is too high, the yield is poor.

[0024] After the preliminary carbonization treatment at a low temperature in advance to form the preliminary carbide, the heat treatment may be performed. The pre-carbonization temperature is usually preferably about 100-400 ° C, more preferably about 150-350 ° C. If the pre-carbonization temperature is too low, a suitable pre-carbide may not be formed, whereas if the pre-carbonization temperature is too high, carbonization may proceed excessively and a suitable pre-carbide may not be obtained. In addition, the yield may decrease There is power ^S.

[0025] The heat treatment time can be appropriately set according to the temperature condition, but is usually about 30 minutes to 5 hours, preferably about 1 to 3 hours. However, the heat treatment time can be appropriately adjusted according to the amount and type of raw materials such as iron salt, nitrogen-containing compound and carbohydrate, and is not necessarily limited to the above range.

[0026] As a result of the heat treatment, a carbon material in which iron is bonded via a nitrogen atom is obtained. In the production method of the present invention, the carbon material may be activated by a known activation method such as a steam activation method after the heat treatment. Moreover, you may mix | blend well-known activators, such as salt 匕 zinc and sodium carbonate, with the iron salt which is a raw material, a nitrogen containing compound, and a carbohydrate. As a result, the specific surface area of the obtained carbon material can be further increased, and the performance as a catalyst can be further enhanced.

[0027] The iron-containing carbon material of the present invention can be applied to various applications by virtue of the feature that iron atoms are stably bonded to the surface of the carbon material. Examples thereof include oxygen reduction electrode materials and electrode catalyst materials for oxygen reduction electrodes of solid polymer electrolyte fuel cells. These typical applications are described below.

[0028] Material of oxygen reduction electrode

The iron-containing carbon material of the present invention is useful as a material for an oxygen reduction electrode. The manufacturing method of the oxygen reduction electrode using the iron-containing carbon material of the present invention is not particularly limited, and a known method can be used. For example, the iron-containing carbon material of the present invention and a known binder such as tetrafluoroethylene can be mixed and then compression molded to obtain oxygen reduction electrodes of various shapes.

[0029] In addition, a conductive agent or the like may be added to the iron-containing carbon material of the present invention to increase electrode activity, thereby forming an oxygen reduction electrode. Carbon black is generally used as the conductive agent. Carbon black having an average particle size of preferably 70 nm or less, more preferably about 10 to 60 nm can be used. The amount of the conductive agent is not particularly limited, but is usually about:! To 200 parts by weight, more preferably about 5 to about 100 parts by weight with respect to 100 parts by weight of the carbon material.

[0030] A metal component may be added as necessary. If the metal component is a metal Any one may be used, but platinum or a platinum alloy is preferable. Further, the carbon material of the present invention can be used as a carrier such as platinum, or an electrode catalyst. However, even when platinum or the like is combined, since the iron-containing carbon material of the present invention has an excellent catalytic action, the amount of platinum or the like used can be significantly reduced as compared with the conventional platinum electrode catalyst.

[0031] · Electrocatalyst material for oxygen reduction electrode of solid polymer electrolyte fuel cell

The iron-containing carbon material of the present invention is particularly useful as an electrode catalyst material for an oxygen reduction electrode of a solid polymer electrolyte fuel cell. The iron-containing carbon material of the present invention can be used as a catalyst as it is, and other components can be added depending on circumstances. For example, there is a case where a conductive agent such as carbon black is added for the purpose of improving conductivity. Further, the iron-containing carbon material of the present invention can be used as a carrier having catalytic activity, and a metal or a noble metal can be further supported.

[0032] The method for forming the oxygen reduction electrode of the solid polymer electrolyte fuel cell using the iron-containing carbon material of the present invention is not particularly limited, and can be formed according to a conventional method. For example, the iron-containing carbon material of the present invention can be used as a catalyst, and this can be applied to a solid polymer electrolyte membrane made of a proton conductive material or an anion conductive material to form an electrode. An example of manufacturing an electrode using a proton conductive material is shown below, but other conventional manufacturing methods are not excluded depending on the performance and form of the electrode.

[0033] (1) The carbon material of the present invention and a proton conductive material are mixed in a medium to form a paste-like electrode catalyst layer forming material, which is directly applied to the proton conductive film and then applied. The oxygen reduction electrode can also be formed by drying.

[0034] The proton conductive substance can be used without particular limitation as long as it can transmit protons. For example, fluorine-containing ion exchange resins having a sulfonic acid group, such as naphthion (manufactured by DuPont), Flemion (manufactured by Asahi Glass), and Aciplex (manufactured by Asahi Kasei).

[0035] As the proton conductive membrane, it is possible to use the same material as the proton conductive material used as the electrode catalyst layer forming material, that is, a membrane formed of a fluorine-based resin having a sulfonic acid group. it can.

[0036] (2) The carbon material of the present invention, a known conductive agent such as carbon black, and a proton conductive material The oxygen reduction electrode can also be formed by mixing the material in a medium to obtain a paste-like electrode catalyst layer forming material, which is directly applied to the proton conductive membrane and drying the applied layer.

[0037] As described above, the method for forming the electrode catalyst layer is as follows: 1) Only the method (coating method) of applying the paste-like electrode catalyst layer forming material directly on the surface of the proton conductive membrane 2) A method of transferring the electrode catalyst layer to the proton conductive membrane side after applying the paste-like electrode catalyst layer forming material on a sheet-like substrate such as a tetrafluoroethylene sheet to form the electrode catalyst layer (transfer Law) etc. can also be used.

[0038] As the conductive agent, those described in the item (Material for oxygen reduction electrode) can be used. Thus, when a electrically conductive agent is mix | blended, activity can be improved more. A metal component can be added as necessary. The metal component may be any metal as long as it is a metal, but is preferably platinum or a platinum alloy. Further, the carbon material of the present invention can be used as a support of platinum or the like to form an electrode catalyst.

[0039] The medium may be any medium as long as it acts as a medium for the iron-containing carbon material or proton conductive material of the present invention. For example, alcohol, water, or these Can be used. In order to prepare a paste-like electrode catalyst layer forming material having a uniform composition of the carbon material of the present invention in the medium, it is particularly preferable to perform ultrasonic vibration stirring and the like.

[0040] Next, an oxygen reduction electrode of a solid polymer electrolyte fuel cell can be produced by bonding the formed electrode catalyst layer and a porous conductive sheet-like substrate such as carbon paper. In addition, after applying the paste-like electrode catalyst layer forming material on the porous conductive sheet-like base material to form the electrode catalyst layer, the method of joining the surface of the electrode catalyst layer to the proton conductive membrane is adopted. Also good.

[0041] The oxygen reduction electrode of the solid polymer electrolyte fuel cell produced as described above exhibits high activity for the oxygen reduction reaction even if it does not contain platinum which has been conventionally used as a catalyst component. In addition, it has the ability to reduce oxygen directly to water in the same way as an electrode using platinum, which generates a small amount of intermediate hydrogen peroxide, which can cause a decrease in fuel cell efficiency and material deterioration. Is very good at. High catalytic performance especially in alkaline environment Therefore, for example, in a polymer electrolyte fuel cell using an anion exchange type solid polymer electrolyte, excellent oxygen reduction performance can be exhibited.

Example

[0042] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the examples.

[0043] Example 1

(1) Manufacture of iron-containing carbon materials

Iron lactate (II) trihydrate was used as the iron salt, glycine, which is an amino acid as the nitrogen-containing compound, and gnolecose as the carbohydrate, and these were mixed and powdered in a mortar. The molar ratio of glycine to gnoleose was 1: 1, and the iron content in the mixture was 1% by weight. Dehydration, often performed before carbonization of common sugars, was carried out by holding in air at 150 ° C for 24 hours. The obtained precursor was powdered, heated in an inert gas argon at 1000 ° C. at a heating rate of 5 ° C./min, and then heat-treated at 1000 ° C. for 2 hours. Yield was obtained from mass change before and after heat treatment. The obtained iron-containing carbon material was pulverized and then treated in boiling sulfuric acid aqueous solution to remove unnecessary soluble iron. The atomic ratio of carbon, nitrogen, oxygen, and iron on the surface of the obtained iron-containing carbon material was determined by X-ray photoelectron spectroscopy. These results are shown in Table 1 below.

[0044] (2) Formation of electrode catalyst layer

50 mg of the above carbon material containing iron was added to carbon black (trade name “Vulcan XC-7

2R "manufactured by Cabot Corporation) with 5 mg, 5 wt ^_0/0 per full O b sulfonic acid resin solution (manufactured by Aldo rich Inc.) 0. 5 ml was added to a solution in lml with ultrapure water, and ultrasonically dispersed A catalyst paste was prepared.

[0045] The catalyst paste 2 µ 1 was applied to a rotating glass one carbon disk electrode at an application area of 0.071 cm ² and sufficiently dried to form an electrode catalyst layer.

[0046] The rotating electrode on which the electrode catalyst layer was formed was immersed in a 0.1 mol / perchloric acid aqueous solution saturated with oxygen, and the relationship between the oxygen reduction current and the electrode potential was measured using the reversible hydrogen electrode (RHE) as a reference electrode. Examined. Figure 1 shows the relationship.

[0047] Activity evaluation for oxygen reduction reaction of electrode catalyst layer and number of reaction electrons per molecule of oxygen Was measured according to the rotating electrode method. The rotating electrode method is, for example, “Journal”

'The Elect Mouth Chemical Society, No. 145, 1998, p. 3713' "and 'Journal' Ob 'The' Elect Mouth Chemical 'Society, p. 146, 1999, p. 1296" It has been reported that it is effective in evaluating the electrocatalytic activity of solid polymer electrolyte fuel cells and has a good correlation with fuel cell performance. The number of reaction electrons per molecule of oxygen is shown in Table 2 below.

[0048] Example 2

(1) Manufacture of iron-containing carbon materials

An iron-containing carbon material was produced in the same manner as in Example 1 except that adenine, which is a purine base, was used in place of glycine as the nitrogen-containing compound. Yield was obtained from mass change before and after heat treatment. The obtained iron-containing carbon material was pulverized and then treated in boiling sulfuric acid aqueous solution to remove unnecessary soluble iron. The atomic ratio of carbon, nitrogen, oxygen, and iron on the surface of the obtained iron-containing carbon material was determined by X-ray photoelectron spectroscopy. These results are shown in Table 1 below.

[0049] (2) Formation of electrode catalyst layer

An electrode catalyst layer was formed in the same manner as in Example 1.

[0050] In the same manner as in Example 1, the relationship between the oxygen reduction current and the electrode potential was examined for the rotating electrode on which the electrode catalyst layer was formed. Figure 1 shows the relationship.

[0051] In the same manner as in Example 1, the number of reaction electrons per oxygen molecule in the electrode catalyst layer was measured.

Table 2 shows the number of reaction electrons per molecule of oxygen.

[0052] Example 3

(1) Manufacture of metal-containing carbon materials

Example 2 except that iron (II) lactate is used instead of iron (II) lactate as the iron salt, and copper (II) is used as the compound containing copper. In the same manner, a metal-containing carbon material was produced. Here, the molar ratio of iron (II) dalconate dihydrate to copper dalconate was 1: 1, and the metal content in the starting material mixture was 1% by weight. The yield was determined from the mass change before and after the heat treatment. The obtained metal-containing carbon material was pulverized and then treated in boiling sulfuric acid solution to remove unnecessary soluble metal components. Obtained iron-containing carbon material table The atomic ratio of carbon, nitrogen, oxygen, iron and copper on the surface was determined by X-ray photoelectron spectroscopy. These results are shown in Table 1 below.

[0053] (2) Formation of electrode catalyst layer

An electrode catalyst layer was formed in the same manner as in Example 1.

[0054] In the same manner as in Example 1, the relationship between the oxygen reduction current and the electrode potential was examined for the rotating electrode on which the electrode catalyst layer was formed. Figure 1 shows the relationship.

[0055] In the same manner as in Example 1, the number of reaction electrons per oxygen molecule in the electrode catalyst layer was measured.

Table 2 shows the number of reaction electrons per molecule of oxygen.

[0056] [Table 1]

[0057] [Table 2]

[0058] Comparative Example 1

(1) Formation of electrode catalyst layer

Carbon black (trade name “Vulcan XC-72R” manufactured by Cabot) 10 mg of 5 wt% perfluorosulfonic acid resin solution (Aldrich) Catalyst paste by placing in lml and dispersing by ultrasound Was prepared.

[0059] 1 μ 1 of the catalyst paste was applied to a rotating glass one carbon disk electrode at an application area of 0.071 cm ² and sufficiently dried to form an electrode catalyst layer.

[0060] In the same manner as in Example 1, the relationship between the oxygen reduction current and the electrode potential was examined for the rotating electrode on which the electrode catalyst layer was formed. Figure 1 shows the relationship. [0061] Example 4

(1) Formation of electrode catalyst layer

The iron-containing carbon material lOmg obtained in Example 1 was added to a 2.5% by weight anion exchange resin solution together with lmg of carbon black (trade name “Vulcan XC-72R” manufactured by Cabot), and dispersed by an ultrasonic wave to form a catalyst. A paste was prepared. The catalyst paste was applied to a single bon disc electrode with a rotating glass, and dried sufficiently at room temperature to form an electrode catalyst layer.

[0062] The rotating electrode on which the electrocatalyst layer was formed was immersed in an lmol / 1 potassium hydroxide aqueous solution saturated with oxygen, and the relationship between the oxygen reduction current and the electrode potential was investigated using a reversible hydrogen electrode (RHE) as a reference electrode. It was. Figure 2 shows this relationship. Table 3 shows the number of reaction electrons per oxygen molecule.

[0063] Example 5

(1) Formation of electrode catalyst layer

The iron-containing carbon material lOmg obtained in Example 2 was added to a 2.5% by weight anion exchange resin solution together with lmg of carbon black (trade name “Vulcan XC-72R” manufactured by Cabot Corporation), and dispersed by ultrasonic to form a catalyst. A paste was prepared. The catalyst paste was applied to a single bon disc electrode with a rotating glass, and dried sufficiently at room temperature to form an electrode catalyst layer.

[0064] The rotating electrode on which the electrode catalyst layer was formed was immersed in an lmol / 1 potassium hydroxide aqueous solution saturated with oxygen, and the relationship between the oxygen reduction current and the electrode potential was investigated using the reversible hydrogen electrode (RHE) as a reference electrode. It was. Figure 2 shows this relationship. Table 3 shows the number of reaction electrons per oxygen molecule.

[0065] Comparative Example 2

(1) Formation of electrode catalyst layer

Commercially available Ag-based catalyst (E-TEK, Ag loading: 60% by mass, support: carbon black Vulcan XC-72) lOmg is added to a 2.5 wt% anion exchange resin solution and dispersed by ultrasound. A catalyst paste was prepared. The catalyst paste was applied to a rotating glass / carbon disk electrode and sufficiently dried at room temperature to form an electrode catalyst layer.

[0066] The rotating electrode on which the electrocatalyst layer was formed was immersed in an lmol / 1 potassium hydroxide aqueous solution saturated with oxygen, and the relationship between the oxygen reduction current and the electrode potential using a reversible hydrogen electrode (RHE) as a reference electrode. I checked the staff. Figure 2 shows this relationship. Table 3 shows the number of reaction electrons per oxygen molecule.

[0067] [Table 3]

[0068] Discussion of results

From Table 1, the iron-containing carbon material of the present invention is mostly carbon, but has functional groups containing oxygen atoms on its surface, and further, iron and nitrogen atoms exist on the surface and are active. It is suggested that this is a point.

[0069] Table 2 shows that the iron-containing carbon material of the present invention is used in comparison with the number of reaction electrons per molecule of oxygen in an acidic environment is 4, which is the number of reaction electrons when directly reduced to water. It can be seen that the oxygen reduction electrode has the ability to reduce oxygen directly to water with little production of hydrogen peroxide, an intermediate equivalent to 2 reaction electrons.

[0070] Table 3 shows that when the iron-containing carbon material of the present invention is used as a material for an oxygen reduction electrode, the number of reaction electrons per molecule of oxygen is higher than that of a commercially available Ag-based catalyst. It can be seen that the contained carbon material has excellent catalytic ability to reduce oxygen directly to water.

From FIG. 1, it can be seen that the electrode catalyst layer containing the iron-containing carbon material of the present invention has excellent oxygen reduction performance in an acidic environment.

FIG. 2 shows that the electrode catalyst layer containing the iron-containing carbon material of the present invention has excellent oxygen reduction performance even in an alkaline environment.

Industrial applicability

[0073] The iron-containing carbon material obtained by the production method of the present invention is preferably a material for an oxygen reduction electrode in which iron and nitrogen atoms are incorporated into the carbon material during heat treatment to form a stable active site for an oxygen reduction reaction. It becomes. The oxygen reduction electrode containing the carbon material of the present invention exhibits high activity for the oxygen reduction reaction. In addition, the iron-containing carbon material of the present invention, when used as a material for an oxygen reduction electrode, produces a low amount of hydrogen peroxide, which is an intermediate that can cause a decrease in battery efficiency and deterioration of the material. It ’s also excellent in terms. Such an oxygen reduction electrode is useful as an electrode of, for example, an alkaline fuel cell or a phosphoric acid fuel cell. That In addition, it is also useful as a component of a salt electrolysis layer, an air zinc battery, or the like.

[0074] The iron-containing carbon material of the present invention is particularly useful as an electrode catalyst material for an oxygen reduction electrode of a solid polymer electrolyte fuel cell. An oxygen reduction electrode of a solid polymer electrolyte fuel cell using the carbon material of the present invention as an electrode catalyst exhibits high activity for an oxygen reduction reaction even if platinum which has been conventionally used as an electrode catalyst material is not included. In addition, it has the ability to directly reduce oxygen to water, as well as an electrode using platinum, which produces a small amount of hydrogen peroxide, which is an intermediate that can cause fuel cell efficiency degradation and material degradation. Very good. In particular, since high catalyst performance can be exhibited in an alkaline environment, excellent oxygen reduction performance can be exhibited, for example, in a solid polymer fuel cell using an anion exchange type solid polymer electrolyte.

[0075] According to the production method of the present invention, the above iron-containing carbon material can be produced inexpensively and easily without using an expensive raw material or a raw material that requires labor for preparation. Therefore, the present invention is extremely useful industrially as being able to contribute to the practical use of fuel cells.

Claims

The scope of the claims

[1] mixing an iron salt, a nitrogen-containing compound and a carbohydrate; and

Heat treating the mixture in an inert atmosphere;

A method for producing an iron-containing carbon material, comprising:

[2] In the process of mixing iron salt, nitrogen-containing compound and carbohydrate, in addition to iron salt, copper salt, nickel salt, cobalt salt, chromium salt, manganese salt, and vanadium salt strength The method for producing an iron-containing carbon material according to claim 1, wherein at least one selected from the above is mixed.

[3] An iron-containing carbon material produced by the method according to claim 1 or 2

[4] An oxygen reduction electrode comprising the iron-containing carbon material according to claim 3.

[5] A solidified polymer fuel cell comprising the oxygen reduction electrode according to claim 4.