JP2008258151A - Electrode catalyst for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode catalyst for a fuel cell excellent in catalyst activity and stability. <P>SOLUTION: The electrode catalyst for a fuel cell uses a mononuclear metal complex with an organic compound comprising two or more phenol rings and three or more aromatic heterocycles as ligand. The organic ligand constituting the mononuclear metal complex comprises divalent organic radical comprising at least one aromatic heterocycle and monovalent organic radical comprising at least one aromatic heterocycle. The metal constituting the mononuclear metal complex comprises transition metal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell electrode catalyst.

  Metal complexes can be regularly integrated with metal atoms and organic ligands to control the arrangement, space, and magnetism, and are expected to be used for gas storage, proton conductors, molecular memory, etc. (Non-Patent Document 1).

Among metal complexes, when having a transition metal atom as a central metal, it is known to have excellent catalytic activity as an oxygen reduction catalyst or a hydrogen peroxide decomposition catalyst (see Non-Patent Document 2 and Non-Patent Document 3). .
In addition, it is known that reactive chemical species are captured and catalytic activity is improved by disposing a substituent that interacts with an acid base in the vicinity of a metal atom (Non-patent Document 4).
However, when a conventional metal complex as described above is used as a catalyst, the stability of the complex is insufficient, and there is a problem particularly when the reaction is performed in the presence of an acid or when the reaction is performed under heating. It was. Therefore, it has been eagerly desired to improve the stability of the metal complex catalyst in the presence of an acid or at a high temperature.

  Non-Patent Document 5 discloses a fuel cell electrode catalyst in which a cobalt mononuclear metal complex is stabilized by heat treatment.

However, the catalytic activity of the metal complex as described in Non-Patent Document 5 is still insufficient, and further improvement of the catalytic activity has been desired.
Susumu Kitagawa, Ryo Kitaura, Shin-ichiro Noro, Angelwandte Chemie International Edition, 43, 2334 (2004). Z. Liu, F .; C. Anson, Inorganic Chemistry, 40, 1329 (2001). M.M. D. Godbole et al., European Journal of Inorganic Chemistry, 305 (2005). S. -Y. Liu, D .; G. Nocara, Journal of American Chemical Society, 127, 5278 (2005). Tatsuhiro Okada, et. al. Journal of Inorganic and Organometallic Polymers, 9, 199, (1999).

  An object of the present invention is to provide a fuel cell electrode catalyst having excellent catalytic activity and stability.

  The present inventors have found that introduction of a plurality of phenol rings and a plurality of aromatic heterocycles into a ligand of a mononuclear metal complex is effective in improving catalytic activity and stability, and these findings Based on the above, the present invention was completed by repeated testing.

The object of the present invention is achieved by means shown in the following (1) to (7).
(1) A fuel cell electrode catalyst using a mononuclear metal complex having an organic compound having two or more phenol rings and three or more aromatic heterocycles as a ligand.
(2) The fuel cell electrode catalyst according to (1), wherein the mononuclear metal complex is represented by the formula (I).

（式中、Ｒ^１は、水素原子または置換基であり、隣合う２つのＲ^１は互いに連結していて
もよく、複数あるＲ^１は、互いに同一であっても異なっていてもよい。Ｑ^１は、少なくと
も１つの芳香族複素環を有する２価の有機基であり、Ｔ^１は、少なくとも１つの芳香族複素環を有する１価の有機基であり、２つのＴ^１は、互いに同一でも異なっていてもよい。Ｍは遷移金属原子を表す。Ｘは、金属錯体を電気的に中性とする対イオン又は中性分子であり、ｎは、錯体中にあるＸの個数であり、０以上の整数を表し、Ｘが複数ある場合それらは互いに同一でも異なっていてもよい。）
（３）式（Ｉ）のＴ^１を構成する芳香族複素環の共役酸の酸解離定数ｐＫａが−２．０以上であることを特徴とする（２）に記載の燃料電池用電極触媒。
（４）前記単核金属錯体が、該単核金属錯体に１つの酸素分子を吸着させ、該１つの酸素分子を構成する２つの酸素原子のＭｕｌｌｉｋｅｎ電荷を密度汎関数法で計算したとき、該２つの酸素原子のＭｕｌｌｉｋｅｎ電荷の差の絶対値が０．０２０〜０．０６２であることを特徴とする（１）〜（３）の何れかに記載の燃料電池用電極触媒。
（５）前記単核金属錯体が、該単核金属錯体に１つの酸素分子を吸着させ、該１つの酸素分子を構成する２つの酸素原子のＭｕｌｌｉｋｅｎ電荷を密度汎関数法で計算したとき、該２つの酸素原子のＭｕｌｌｉｋｅｎ電荷の和が−０．２５以上であることを特徴とする（１）〜（４）の何れかに記載の燃料電池用電極触媒。
（６）（１）〜（５）の何れかに記載の単核金属錯体を２５０℃以上１５００℃以下の温度にて加熱することにより得られる燃料電池用電極錯体。
（７）（１）〜（５）の何れかに記載の単核金属錯体と、カーボン担体及び／又は導電性高分子とを含む単核金属錯体混合物を用いてなる燃料電池用電極触媒。
（８）（１）〜（５）の何れかに記載の単核金属錯体と、カーボン担体及び／又は導電性高分子とを含む単核金属錯体混合物を２５０℃以上１５００℃以下の温度にて加熱することにより得られる燃料電池用電極触媒。

(In the formula, R ¹ is a hydrogen atom or a substituent, and two adjacent R ^{1 s} may be linked to each other, and a plurality of R ¹ may be the same or different from each other. Q ¹ is a divalent organic group having at least one aromatic heterocyclic ring, T ¹ is a monovalent organic group having at least one aromatic heterocyclic ring, and two T ¹ are the same as each other M represents a transition metal atom, X is a counter ion or neutral molecule that electrically neutralizes the metal complex, n is the number of X in the complex, and 0 Represents the above integer, and when there are a plurality of X, they may be the same or different from each other.
(3) The fuel cell electrode catalyst according to (2), wherein the acid dissociation constant pKa of the conjugate acid of the aromatic heterocyclic ring constituting T ¹ of formula (I) is −2.0 or more.
(4) When the mononuclear metal complex adsorbs one oxygen molecule to the mononuclear metal complex, and the Mulliken charges of two oxygen atoms constituting the one oxygen molecule are calculated by a density functional method, 2. The fuel cell electrode catalyst according to any one of (1) to (3), wherein the absolute value of the difference between the Mulliken charges of two oxygen atoms is 0.020 to 0.062.
(5) When the mononuclear metal complex adsorbs one oxygen molecule to the mononuclear metal complex, and the Mulliken charges of two oxygen atoms constituting the one oxygen molecule are calculated by a density functional method, 2. The fuel cell electrode catalyst according to any one of (1) to (4), wherein the sum of Mulliken charges of two oxygen atoms is −0.25 or more.
(6) An electrode complex for a fuel cell obtained by heating the mononuclear metal complex according to any one of (1) to (5) at a temperature of 250 ° C. or higher and 1500 ° C. or lower.
(7) A fuel cell electrode catalyst comprising a mononuclear metal complex mixture comprising the mononuclear metal complex according to any one of (1) to (5) and a carbon support and / or a conductive polymer.
(8) A mononuclear metal complex mixture containing the mononuclear metal complex according to any one of (1) to (5) and a carbon support and / or a conductive polymer at a temperature of 250 ° C. or higher and 1500 ° C. or lower. A fuel cell electrode catalyst obtained by heating.

  By using the mononuclear metal complex of the present invention, a fuel cell electrode catalyst excellent in catalytic activity (for example, mass activity) and stability is provided.

  The mononuclear metal complex used in the present invention has a ligand composed of two or more phenol rings (that is, phenols and / or derivatives thereof) and an organic compound having three or more aromatic heterocycles.

  The number of phenol rings is preferably 2 to 4, more preferably 2 to 3. In addition to the aromatic heterocyclic ring coordinated to the transition metal atom, the aromatic heterocyclic ring must be capable of capturing a reaction intermediate or integrating mononuclear metal complexes. Since it is preferable, the number of aromatic heterocycles is preferably 3 or more and 5 or less.

  Next, the mononuclear metal complex is preferably a metal complex represented by the formula (I). In this metal complex, a transition metal atom M forms a complex with a ligand having at least two oxygen atoms. The bond between the oxygen atom and the metal atom is a coordination bond or an ionic bond. Here, “transition metal” is synonymous with “transition element” described on page 1283 of “Chemical Dictionary” (Michinori Oki et al., Issued July 1, 2005, Tokyo Chemical Doujin). Yes, means an element with an incomplete d or f subshell. The transition metal atom in the present invention may be an uncharged or charged ion.

Here, specific examples of the transition metal include scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, cadmium. , Hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury.
Among these, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, molybdenum, ruthenium, rhodium, palladium, silver, cadmium, tantalum, tungsten, osmium, iridium, platinum, gold , Mercury. Particularly preferred are vanadium, chromium, manganese, iron, cobalt, nickel and copper, and more preferred are iron, cobalt, nickel and copper.

The substituent represented by R ¹ in the general formula (I) is a hydroxy group, an amino group, a nitro group, a cyano group, a carboxyl group, a formyl group, a sulfonyl group, a halogen atom, or an optionally substituted monovalent group. A hydrocarbon group, an optionally substituted hydrocarbyloxy group (an optionally substituted hydrocarbonoxy group), an amino group substituted with two unsubstituted or substituted monovalent hydrocarbon groups (ie, substituted Optionally substituted hydrocarbon di-substituted amino group), optionally substituted hydrocarbyl mercapto group (optionally substituted hydrocarbon mercapto group) optionally substituted hydrocarbyl carbonyl group (optionally substituted). Hydrocarbon carbonyl group), optionally substituted hydrocarbyloxycarbonyl group (optionally substituted hydrocarbon oxycarbonyl group), non-substituted An aminocarbonyl group substituted by two substituted or substituted monovalent hydrocarbon groups (that is, an optionally substituted hydrocarbon disubstituted aminocarbonyl group), or an optionally substituted hydrocarbyloxysulfonyl group (substituted) An optionally substituted hydrocarbon sulfonyl group), an optionally substituted monovalent hydrocarbon group, an optionally substituted hydrocarbyloxy group, two unsubstituted or substituted monovalent hydrocarbon groups. A substituted amino group, an optionally substituted hydrocarbyl mercapto group, an optionally substituted hydrocarbylcarbonyl group, and an optionally substituted hydrocarbyloxycarbonyl group are preferred, and an optionally substituted monovalent hydrocarbon A substituted or unsubstituted hydrocarbyloxy group, an unsubstituted or substituted monovalent hydrocarbon group More preferably amino group, 1 may be substituted monovalent hydrocarbon group, an optionally substituted hydrocarbyloxy group is more preferred. In these groups, the nitrogen atom to which a hydrogen atom is bonded is preferably substituted with a monovalent hydrocarbon group. Moreover, when the group represented by R ¹ has a plurality of substituents, the two substituents may be linked to form a ring.

Examples of the monovalent hydrocarbon group represented by R ¹ include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, and hexyl. Group, nonyl group, dodecyl group, pentadecyl group, octadecyl group, docosyl group, etc., an alkyl group having 1 to 50 carbon atoms (preferably an alkyl group having 1 to 20 carbon atoms); cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclo Hexyl group, cyclononyl group, cyclododecyl group, norbornyl group, adamantyl group and other cyclic saturated hydrocarbon groups having 3 to 50 carbon atoms (preferably cyclic saturated hydrocarbon groups having 3 to 20 carbon atoms); ethenyl group and propenyl group 3-butenyl group, 2-butenyl group, 2-pentenyl group, 2-hexenyl group, 2-nonenyl group, 2-dodecenyl group An alkenyl group having 2 to 50 carbon atoms (preferably an alkenyl group having 2 to 20) such as a group; phenyl group, 1-naphthyl group, 2-naphthyl group, 2-methylphenyl group, 3-methylphenyl group, 4-methyl Phenyl group, 4-ethylphenyl group, 4-propylphenyl group, 4-isopropylphenyl group, 4-butylphenyl group, 4-tert-butylphenyl group, 4-hexylphenyl group, 4-cyclohexylphenyl group, 4-adamantyl Aryl groups having 6 to 50 carbon atoms such as phenyl group and 4-phenylphenyl group (preferably 6 to 20 aryl groups); phenylmethyl group, 1-phenylethyl group, 2-phenylethyl group, 1-phenyl-1-propyl Group, 1-phenyl-2-propyl group, 2-phenyl-propyl group, 3-phenyl-1-propyl group, 4-phenyl 1-butyl group, 5-phenyl-1-pentyl group, 6-phenyl-1- (preferably an aralkyl group having 7 to 20) aralkyl group having 7 to 50 carbon atoms such as a hexyl group include.

The monovalent hydrocarbon group represented by R ¹ is preferably those having 1 to 20 carbon atoms, more preferably those having 1 to 12 carbon atoms, more preferably those having 2 to 12 carbon atoms, and 1 carbon atom. To 10 carbon atoms are more preferable, those having 3 to 10 carbon atoms are more preferable, alkyl groups having 1 to 10 carbon atoms are particularly preferable, and alkyl groups having 3 to 10 carbon atoms are particularly preferable.

The hydrocarbyloxy group, hydrocarbyl mercapto group, hydrocarbylcarbonyl group, hydrocarbyloxycarbonyl group, and hydrocarbylsulfonyl group represented by R ¹ are the same as the above-mentioned 1 to oxy group, mercapto group, carbonyl group, oxycarbonyl group, and sulfonyl group, respectively. This is a group formed by bonding one valent hydrocarbon group.

R ¹ represents an “amino group substituted with two unsubstituted or substituted monovalent hydrocarbon groups”, “an amino group substituted with two unsubstituted or substituted monovalent hydrocarbon groups” The carbonyl group '' is a group in which two hydrogen atoms in an amino group and an aminocarbonyl group (that is, —C (═O) —NH ₂ ) are substituted with the monovalent hydrocarbon group. . Specific examples and preferred examples of the monovalent hydrocarbon group contained in these are the same as the monovalent hydrocarbon group represented by R ¹ described above.

The monovalent hydrocarbon group represented by R ¹ , hydrocarbyloxy group, hydrocarbyl mercapto group, hydrocarbylcarbonyl group, hydrocarbyloxycarbonyl group, hydrocarbylsulfonyl group, a part or all of the hydrogen atoms contained in these groups, Halogen atom, hydroxyl group, amino group, nitro group, cyano group, monovalent hydrocarbon group which may be substituted, hydrocarbyloxy group which may be substituted, hydrocarbyl mercapto group which may be substituted, substituted It may be substituted with an optionally substituted hydrocarbylcarbonyl group, an optionally substituted hydrocarbyloxycarbonyl group, an optionally substituted hydrocarbylsulfonyl group, and the like.

Among the R ¹ , hydrogen atom, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, phenyl group, methylphenyl group, naphthyl group, and pyridyl are particularly preferable. One or more groups selected from the group.

Specific examples of Q ^{1 in} the general formula (I) include a pyridylene group, a pyrazylene group, a pyrimidylene group, a pyridazylene group, a pyrrolylene group, a furylene group, a thienylene group, a thiazolylene group, an imidazolylene group, an oxazolylene group, a triazorylene group, and an indylene group. , Benzimidazolylene group, benzofurylene group, benzothienylene group, quinolylene group, isoquinolylene group, cinnolylene group, phthalazilene group, quinazolylene group, quinoxarylene group, benzodiazylene group, 1,10-phenanthrolylene group, 2,2'-bipyridylene group 2,2'-bithiophenylene group, 2,2'-bipyrrolene group, 2,2'-bithiazolylene group, 2,2'-bifurylene group, 2,2'-bipyrimidylene group, 2,2'-bipyridazilene group , 2,2'-biimidazolylene group is preferred. Or pyridylene group, pyrazylene group, pyrimidylene group, pyridazylene group, pyrrolylene group, furylene group, thienylene group, 1,10-phenanthrolylene group, 2,2'-bipyridylene group, 2,2'-bithiophenylene. Group, 2,2'-bipyrrolene group, 2,2'-bithiazolylene group, 2,2'-bifurylene group, 2,2'-bipyrimidylene group, 2,2'-bipyridazilene group, 2,2'-biimidazolylene group And more preferably a 1,10-phenanthrolylene group, a 2,2′-bipyridylene group, a 2,2′-bipyrrolene group, a 2,2′-bithiazolylene group, or a 2,2′-biimidazolylene group. In addition, these groups may be further substituted with the substituents mentioned in the section for R ¹ .

Specific examples of the monovalent organic group having an aromatic heterocyclic ring represented by T ¹ in the general formula (I) include a pyridyl group, a pyrazyl group, a pyrimidyl group, a pyridazyl group, a pyrrolyl group, a furyl group, and a thienyl group. , Thiazolyl group, imidazolyl group, oxazolyl group, triazolyl group, indolyl group, benzoimidazolyl group, benzofuryl group, benzothienyl group, quinolyl group, isoquinolyl group, cinnolyl group, phthalazyl group, quinazolyl group, quinoxalyl group, benzodiazepinyl group, And so on. Further, these groups may be further substituted with the substituent of R ¹ .

The aromatic heterocyclic group constituting T ¹ in the general formula (I) is preferably an aromatic heterocyclic ring in which the acid dissociation constant (pKa) of the conjugate acid is −2.0 or more. Specific examples of the monovalent organic group T ₁ having an aromatic heterocyclic ring include a pyridyl group (pyridine, pKa 5.23), a pyrazyl group (pyrazine, pKa 1.00), and a pyridazyl group (pyridazine, pKa2. 34), pyrrolyl group (pyrrole, pKa-0.27, 17.00), imidazolyl group (imidazole, pKa 7.18, 14.10), oxazolyl group (oxazole, pKa 0.80), triazolyl group (1H- 1,2,4-triazole, pKa 3.00, 10.18, 1H-1,2,4-triazole, pKa 1.47, 8.73), indolyl group (indole, pKa-0.27, 17. 00), benzimidazolyl group (benzimidazole, pKa 5.67, 12.60), quinolyl group (quinoline, pKa 4.97), isoquino Group (isoquinoline, pKa 5.37), cinnolyl group (cinnoline, pKa 3.00), phthalazyl group (phthalazine, pKa 3.47), quinazolyl group (quinazoline, pKa 3.43), quinoxalyl group (quinoxaline, pKa) 0.59), a benzodiazepinyl group (benzodiazepine, pKa 9.57), and the like. Here, pKa is a predicted value at 25 ° C. in water according to Advanced Chemistry Development (ACD / Labs) Software registered in Sciffender. The value of pKa is more preferably 0 or more, and further preferably 2 or more. The pKa is preferably 20 or less, more preferably 18 or less.

The mononuclear metal complex used as the electrode catalyst for a fuel cell according to the present invention includes a single functional oxygen molecule adsorbed on the mononuclear metal complex, and the Mulliken charges of the two oxygen atoms constituting the single oxygen molecule. When calculated by the method, the absolute value of the difference between the Mulliken charges of the two oxygen atoms is preferably 0.020 to 0.062. The Mulliken charge is obtained by a structure optimization calculation based on a density functional method. For the calculation of the Mulliken charge, Gaussian03 is used, B3LYP is used as the functional, LANL2DZ is used as the transition metal atom, and 6-31G (d) is used as the other atoms. When there are multiple stable structures, the most stable structure is adopted.
The absolute value of the difference between the Mulliken charges is preferably 0.030 or more, more preferably 0.040 or more, and particularly preferably 0.050 or more. The absolute value of the difference between the Mulliken charges is preferably 0.060 or less, particularly preferably 0.058 or less.
The mononuclear metal complex used as the electrode catalyst for a fuel cell of the present invention includes a single functional oxygen molecule adsorbed on the mononuclear metal complex, and the Mulliken charge of two oxygen atoms constituting the oxygen molecule is expressed as a density functional. When calculated by the method, the sum of the Mulliken charges of the two oxygen atoms is preferably −0.25 or more. The Mulliken charge is obtained by a structure optimization calculation based on the density functional method.
The sum of the Mulliken charges is preferably −0.23 or more, more preferably −0.20 or more, and particularly preferably −0.17 or more. The sum of the Mulliken charges is preferably 0.00 or less, more preferably −0.05 or less, and particularly preferably −0.10 or less.

  The mononuclear metal complex represented by the general formula (I) is preferably a mononuclear metal complex represented by the following formula (II).

(In the formula, R ² has the same meaning as R ^1, and two adjacent R ² may be linked to each other to form a ring. Y ¹ and Y ² are each independently

(Wherein, R _a is a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms). P1 and P2 are each independently, together with Y ¹ and Y ² represents a divalent aromatic heterocyclic group, P1 and P2 may form a further bond to ring. M, X, and n have the same meaning as M, X, and n in the general formula (I). T ² has the same meaning as T ¹ . )

Specific examples of P1 and P2 in the general formula (II) include pyridylene group, pyrazylene group, pyrimidylene group, pyrrolylene group, furylene group, thienylene group, thiazolylene group, imidazolylene group, oxazolylene group, triazolylene group, indolylene group, benzimidazolylene. Group, benzofurylene group, benzothienylene group, isoquinolylene group, cinnolylene group, phthalazilene group, quinazolylene group, quinoxalylene group, preferably pyridylene group, pyrazylene group, pyrimidylene group, pyrrolylene group, furylene group, thienylene group, Preferred are a pyridylene group, a pyrrolylene group, a furylene group, and a thienylene group. P1, 2-valent aromatic heterocyclic group represented by P2 may be substituted with a substituent of R ^1.
P1 and P2 may be bonded to each other to form a new ring, and the mononuclear metal complex preferably has the following structures (III-a) to (III-i): And those having the structures of (III-a) to (III-d) are more preferred.

Here, R ³ represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms.
In addition, a part or all of the hydrogen atoms in the divalent aromatic heterocyclic group represented by P1 and P2 may be substituted with the substituent of R ¹ exemplified above.
The ligand part of the mononuclear metal complex represented by the general formula (II) is described in non-patent document Tetrahedron, 55, 8377 (1999). Can be synthesized by an addition reaction and oxidation of an organometallic reagent to a heterocyclic ring, a halogenation reaction, and then a cross-coupling reaction using a transition metal catalyst. Moreover, it is also possible to synthesize stepwise by a cross-coupling reaction using a halide of a compound having a heterocyclic ring.

As the ligand moiety of the mononuclear metal complex represented by the formula (II), those having structures represented by the following formulas (IV-1) to (IV-18) are preferable. Among these, preferably, it has a structure represented by (IV-1) to (IV-12), and particularly preferably has a structure represented by (IV-1) to (IV-6). Is.
In the formula, Me represents ^methyl, t Bu is tert- butyl, Ph is phenyl.

  X in the formulas (I) and (II) is a neutral molecule or a counter ion that electrically neutralizes the metal complex. Specific examples of the neutral molecule include water, methanol, ethanol, n-propanol, isopropyl alcohol, 2-methoxyethanol, 1,1-dimethylethanol, ethylene glycol, N, N′-dimethylformamide, N, N′-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, acetone, chloroform, acetonitrile, benzonitrile, triethylamine, pyridine, pyrazine, diazabicyclo [2,2,2] octane, 4,4′-bipyridine , Tetrahydrofuran, diethyl ether, dimethoxyethane, methyl ethyl ether, 1,4-dioxane. Preferably, water, methanol, ethanol, isopropyl alcohol, ethylene glycol, N, N′-dimethylformamide, N, N′-dimethylacetamide, N-methyl-2-pyrrolidone, chloroform, acetonitrile, benzonitrile, triethylamine, pyridine, Pyrazine, diazabicyclo [2,2,2] octane, 4,4′-bipyridine, tetrahydrofuran, dimethoxyethane, and 1,4-dioxane.

Further, when X is a counter ion, the transition metal atom and the typical metal atom usually have a positive charge, so an anion that makes this electrically neutral is selected, and fluoride ion, chloride ion, Bromide ion, iodide ion, sulfide ion, oxide ion, hydroxide ion, hydride ion, sulfite ion, phosphate ion, cyanide ion, acetate ion, carbonate ion, sulfate ion, sulfate ion, nitrate ion, bicarbonate ion Trifluoroacetate ion, thiocyanide ion, trifluoromethanesulfonate ion, acetylacetonate, tetrafluoroborate ion, hexafluorophosphate ion, tetraphenylborate ion. Preferably, chloride ion, bromide ion, iodide ion, oxide ion, hydroxide ion, hydride ion, phosphate ion, cyanide ion, acetate ion, carbonate ion, sulfate ion, nitrate ion, acetylacetonate , Tetraphenylborate ion.
When a plurality of X are present, they may be the same or different, and a form in which a neutral molecule and a counter ion coexist is also possible.

  Next, a method for synthesizing a mononuclear metal complex used in the present invention will be described. The metal complex can be obtained by mixing with a reactant that gives a metal atom coordinated by a ligand (hereinafter referred to as “metal-imparting agent”). As the metal-imparting agent, the transition metal acetates, chlorides, sulfates, carbonates and the like exemplified as specific examples can be used.

As described above, the mononuclear metal complex used in the present invention can be prepared by mixing a ligand compound and a metal imparting agent in the presence of an appropriate reaction solvent. Specifically, the reaction solvent includes water, acetic acid, oxalic acid, aqueous ammonia, methanol, ethanol, n-propanol, isopropyl alcohol, 2-methoxyethanol, 1-butanol, 1,1-dimethylethanol, ethylene. Glycol, diethyl ether, 1,2-dimethoxyethane, methyl ethyl ether, 1,4-dioxane, tetrahydrofuran, benzene, toluene, xylene, mesitylene, durene, decalin, dichloromethane, chloroform, carbon tetrachloride, chlorobenzene, 1,2- Examples include dichlorobenzene, N, N′-dimethylformamide, N, N′-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, acetone, acetonitrile, benzonitrile, triethylamine, and pyridine. It may be used a reaction solvent comprising a mixture of two or more, but is preferably one ligand compound and the metal-providing agent is soluble. The reaction temperature is usually −10 to 200 ° C., preferably 0 to 150 ° C., particularly preferably 0 to 100 ° C., and the reaction time is usually 1 minute to 1 week, preferably 5 minutes to 24 hours, particularly preferably 1 hour. It can be carried out in ~ 12 hours. The reaction temperature and reaction time can also be optimized as appropriate depending on the type of ligand compound and metal imparting agent.
As a means for isolating and purifying the produced mononuclear metal complex from the reaction solution after the reaction, an optimum means can be appropriately selected and used from known recrystallization methods, reprecipitation methods or chromatography methods. These means may be combined.
Depending on the type of the reaction solvent, the produced mononuclear metal complex may precipitate, and the precipitated mononuclear metal complex may be separated by filtration or the like, and may be washed or dried as necessary. A mononuclear metal complex can also be isolated and purified.

In preparing the catalyst of the present invention, the above mononuclear metal complex is preferably heat-treated. This heat treatment causes the cleavage of carbon-hydrogen bonds in the mononuclear metal complex and promotes the formation of carbon-carbon bonds in the mononuclear metal complex or between adjacent mononuclear metal complexes, thereby improving the stability of the catalyst. At the same time, it has the effect of imparting conductivity.
Next, the conditions for the heat treatment of the mononuclear metal complex in the present invention will be described in detail.
As the mononuclear metal complex used for the heat treatment, only one mononuclear metal complex may be used, or two or more mononuclear metal complexes may be used.
The mononuclear metal complex is particularly preferably dried for 6 hours or more at a temperature of 15 ° C. or more and 200 ° C. or less and a reduced pressure of 10 Torr or less as a pretreatment for heat treatment. As the pretreatment, a vacuum dryer or the like can be used.

The atmosphere used for the heat treatment of the mononuclear metal complex is a reducing atmosphere such as hydrogen or carbon monoxide, an oxidizing atmosphere such as oxygen, carbon gas, or water vapor, or an inert atmosphere such as nitrogen, helium, neon, argon, krypton, or xenon. An active gas atmosphere, a gas or vapor of a nitrogen-containing compound such as ammonia or acetonitrile, and a mixed gas thereof are preferable. More preferably, in a reducing atmosphere, hydrogen and a mixed atmosphere of hydrogen and the inert gas, in an oxidizing atmosphere, oxygen, a mixed atmosphere of oxygen and the inert gas, or an inert gas atmosphere If so, it is a mixed atmosphere of nitrogen, neon, argon, and these gases.
Moreover, the pressure which concerns on heat processing is although it does not specifically limit, It is preferable in the normal pressure vicinity of about 0.5-1.5 atmospheres.

  The temperature at which the mononuclear metal complex is subjected to heat treatment is preferably 250 ° C. or higher, more preferably 300 ° C. or higher, further preferably 400 ° C. or higher, and particularly preferably 500 ° C. or higher. Moreover, the temperature concerning heat processing becomes like this. Preferably it is 1500 degrees C or less, More preferably, it is 1200 degrees C or less, Most preferably, it is 1000 degrees C or less.

  The treatment time for the heat treatment can be set as appropriate depending on the gas used, the temperature, etc., but in the sealed or ventilated state of the gas, the temperature can be gradually raised from room temperature and reached immediately after reaching the target temperature. Good. Among them, it is preferable to gradually heat the mononuclear metal complex by maintaining the temperature after reaching the target temperature because durability can be further improved. The holding time after reaching the target temperature is preferably 1 to 100 hours, more preferably 1 to 40 hours, still more preferably 2 hours to 10 hours, and particularly preferably 2 to 3 hours. .

  An apparatus for performing the heat treatment is not particularly limited, and examples thereof include a tubular furnace, an oven, a furnace, and an IH hot plate.

  In another embodiment of the fuel cell electrode catalyst of the present invention, a fuel cell electrode catalyst comprising the mononuclear metal complex and a mononuclear metal complex mixture containing a carbon support and / or a conductive polymer is provided. be able to.

  The mixing ratio of the mononuclear metal complex to the carbon carrier and the conductive polymer in the mononuclear metal complex mixture is such that the content of the mononuclear metal complex is relative to the total mass of the mononuclear metal complex, the carbon carrier and the conductive polymer. 1 to 70% by mass is preferably set. The content of the base metal complex is more preferably 2 to 60% by mass, and particularly preferably 3 to 50% by mass.

  Examples of the carbon carrier include Norrit (manufactured by NORIT), Ketjen Black (manufactured by Lion), Vulcan (manufactured by Cabot), Black Pearl (manufactured by Cabot), and acetylene black (manufactured by Chevron) (all products) Name), fullerenes such as C60 and C70, carbon nanotubes, carbon nanohorns, and carbon fibers.

  Such a mononuclear metal complex mixture may be heat-treated to form an electrode catalyst for a fuel cell, and the conditions for the heat treatment are the same as the conditions for heat-treating the mononuclear metal complex alone.

Since the mononuclear metal complex has an aromatic skeleton, both have high heat resistance and acid resistance.
Therefore, since the complex structure is stable even at high temperatures or in the presence of strong acids, which are the operating conditions of the fuel cell, the catalyst performance can be exhibited over a long period of time.
Examples of the conductive polymer include polyacetylene, polyaniline, and polypyrrole. The mononuclear complex, carbon carrier, and conductive polymer may be used alone or in combination of two or more.

  The electrode catalyst for a fuel cell of the present invention can be used as a catalyst for a fuel electrode and an air electrode of a fuel cell, and may be used as a catalyst for both a fuel electrode and an air electrode, or either a fuel electrode or an air electrode. It can also be used as one catalyst.

  The fuel cell using the fuel cell electrode catalyst of the present invention can be used, for example, as a small power source for mobile devices such as an automobile power source, a household power source, a mobile phone, and a portable personal computer.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Synthesis Example 1 [Synthesis of Mononuclear Metal Complex (A)]
The mononuclear metal complex (A) was synthesized according to the following reaction formula.

In addition, the said ligand compound used as the raw material of a metal complex is Tetrahedron, 55, 8377 (1999). It was synthesized by the method described in 1. 50 ml of ethanol containing 0.315 g of the ligand and 0.124 g of cobalt acetate tetrahydrate was placed in a 100 ml eggplant flask and stirred at 80 ° C. for 1 hour. The produced brown precipitate was collected by filtration, washed with ethanol, and then vacuum-dried to obtain a mononuclear metal complex (A) (yield 0.270 g: 81% yield). Elemental analysis _{(%): Calcd for C 42} H 40 CoN 4 O 4; C, 69.70; H, 5.57; N, 7.74. Found: C, 70.01; H, 5.80; N, 7.56. ESI-MS [M + ·]: 687.1

Synthesis Example 2 [Synthesis of mononuclear metal complex (B)]
The mononuclear metal complex (B) was synthesized via compound (A) and compound (B) according to the following reaction formula.

The raw material 2,9-bis (3′-bromo-5′-tert-butyl-2′-methoxyphenyl) -1,10-phenanthroline was obtained from the literature Tetrahedron. , 1999, 55, 8377. Under an argon atmosphere, 3.945 g of 2,9-bis (3′-bromo-5′-tert-butyl-2′-methoxyphenyl) -1,10-phenanthroline, 3.165 g of 1-N-Boc— Pyrrole-2-boronic acid, 0.138 g of tris (benzylideneacetone) dipalladium, 0.247 g of 2-dicyclohexylphosphino-2 ′, 6′-dimethoxybiphenyl, 5.527 g of potassium phosphate and 200 mL of dioxane It melt | dissolved in the mixed solvent of 20 mL water, and stirred at 60 degreeC for 6 hours. After completion of the reaction, the mixture was allowed to cool, distilled water and chloroform were added, and the organic layer was extracted. The resulting organic layer was concentrated to give a black residue. This was refine | purified using the silica gel column, and the compound (A) was obtained. ¹ H-NMR (300 MHz, CDCl ₃ ) δ 1.34 (s, 18H), 1.37 (s, 18H), 3.30 (s, 6H), 6.21 (m, 2H), 6.27 ( m, 2H), 7.37 (m, 2H), 7.41 (s, 2H), 7.82 (s, 2H), 8.00 (s, 2H), 8.19 (d, J = 8 .6 Hz, 2H), 8.27 (d, J = 8.6 Hz, 2H).

窒素雰囲気下で０．９０４ｇの化合物（Ａ）を１０ｍＬの無水ジクロロメタンに溶解させる。ジクロロメタン溶液を−７８℃に冷却しながら、８．８ｍＬの三臭化ホウ素（１．０Ｍジクロロメタン溶液）をゆっくり滴下した。滴下後、１０分間そのまま攪拌させた後、室温まで攪拌させながら放置した。３時間後、反応溶液を０℃まで冷却させ、飽和ＮａＨＣＯ_３水溶液を加えたのち、クロロホルムを加えて抽出し、有機層を濃縮した。得られた褐色の残渣を、シリカゲルカラムで精製し、化合物（Ｂ）を得た。^１Ｈ−ＮＭＲ（３００ＭＨｚ， ＣＤＣｌ_３）δ１．４０（ｓ， １８Ｈ）， ６．２５（ｍ， ２Ｈ）， ６．４４（ｍ， ２Ｈ）， ６．７４（ｍ， ２Ｈ）， ７．８４（ｓ， ２Ｈ）， ７．８９（ｓ， ２Ｈ）， ７．９２（ｓ， ２Ｈ）， ８．３５（ｄ， Ｊ＝８．４Ｈｚ， ２Ｈ）， ８．４６（ｄ， Ｊ＝８．４Ｈｚ， ２Ｈ）， １０．６１（ｓ， ２Ｈ）， １５．８８（ｓ， ２Ｈ）．

Under a nitrogen atmosphere, 0.904 g of compound (A) is dissolved in 10 mL of anhydrous dichloromethane. While the dichloromethane solution was cooled to −78 ° C., 8.8 mL of boron tribromide (1.0 M dichloromethane solution) was slowly added dropwise. After dropping, the mixture was allowed to stir for 10 minutes and then allowed to stand while stirring to room temperature. After 3 hours, the reaction solution was cooled to 0 ° C., saturated aqueous NaHCO ₃ solution was added, chloroform was added for extraction, and the organic layer was concentrated. The resulting brown residue was purified with a silica gel column to obtain compound (B). ¹ H-NMR (300 MHz, CDCl ₃ ) δ 1.40 (s, 18H), 6.25 (m, 2H), 6.44 (m, 2H), 6.74 (m, 2H), 7.84 ( s, 2H), 7.89 (s, 2H), 7.92 (s, 2H), 8.35 (d, J = 8.4 Hz, 2H), 8.46 (d, J = 8.4 Hz, 2H), 10.61 (s, 2H), 15.88 (s, 2H).

窒素雰囲気下において、０．１００ｇの化合物（Ｂ）と０．０４０ｇの酢酸コバルト４水和物を含んだ２０ｍｌのＡｒで脱気したアセトニトリル溶液を、１００ｍｌの二口フラスコに入れ、室温にて攪拌した。この溶液にトリエチルアミンを４５μｌ滴下し、３時間還流した。この溶液を濃縮し、冷却した後、メンブレンフィルターで濾取し、乾燥することで単核金属錯体（Ｂ）を得た（収量０．０９８ｇ）。ＥＳＩ−ＭＳ［Ｍ＋・］ ：６６３．１。

Under a nitrogen atmosphere, 20 ml of Ar solution degassed with 20 ml of Ar containing 0.100 g of compound (B) and 0.040 g of cobalt acetate tetrahydrate was placed in a 100 ml two-necked flask and stirred at room temperature. did. To this solution, 45 μl of triethylamine was added dropwise and refluxed for 3 hours. The solution was concentrated and cooled, and then filtered through a membrane filter and dried to obtain a mononuclear metal complex (B) (yield 0.098 g). ESI-MS [M +.]: 663.1.

Synthesis Example 3 [Synthesis of Mononuclear Metal Complex (C)]
The mononuclear metal complex (C) was prepared according to the following reaction formula in the document Tatsuhiro Okada, et. al. Journal of Inorganic and Organometallic Polymers, 9, 199 (1999). It was synthesized by the method described in 1.

Synthesis Example 4 [Synthesis of mononuclear metal complex (D)]
A mononuclear metal complex (D) was synthesized according to the following reaction formula.

30 ml of ethanol containing 0.250 g of ligand and 0.100 g of nickel acetate tetrahydrate was placed in a 50 ml eggplant flask and stirred at 80 ° C. for 2 hours. The produced orange precipitate was collected by filtration, washed with ethanol, and then vacuum dried to obtain a mononuclear metal complex (D) (yield 0.242 g: 89% yield). Elemental analysis _{(%): Calcd for C 42} H 36 N 4 NiO 2; C, 73.38; H, 5.28; N, 8.15. Found: C, 72.42; H, 5.27; N, 7.96. ESI-MS [M +.]: 687.1.

Synthesis Example 5 [Synthesis of Mononuclear Metal Complex (E)]
A mononuclear metal complex (E) was synthesized according to the following reaction formula.

30 ml of ethanol containing 0.315 g of ligand and 0.100 g of copper acetate monohydrate was placed in a 50 ml eggplant flask and stirred at 80 ° C. for 2 hours. The produced ocherous precipitate was collected by filtration, washed with ethanol, and vacuum dried to obtain a mononuclear metal complex (E) (yield 0.250 g: yield 72%). Elemental analysis _{(%): Calcd for C 42} H 36 CuN 4 O 2; C, 72.87; H, 5.24; N, 8.09. Found: C, 72.22; H, 5.37; N, 7.77. ESI-MS [M +.]: 692.1.

Synthesis Example 6 [Synthesis of Mononuclear Metal Complex (F)]
A mononuclear metal complex (F) was synthesized according to the following reaction formula.

30 ml of ethanol containing 0.440 g of ligand and 0.120 g of iron acetate was placed in a 50 ml eggplant flask and stirred at 80 ° C. for 2 hours. The produced orange precipitate was collected by filtration, washed with ethanol, and then vacuum dried to obtain a mononuclear metal complex (F) (yield 0.380 g: yield 80%). Elemental analysis _{(%): Calcd for C 42} H 36 FeN 4 O 2; C, 73.68; H, 5.30; N, 8.18. Found: C, 72.20; H, 5.42; N, 7.85. ESI-MS [M +.]: 684.0.

Example 1 (Evaluation of oxygen reduction ability)
[Preparation of electrode catalyst]
A mononuclear metal complex (A) and a carbon support (Ketjen Black EC300J, manufactured by Lion Corporation) were mixed at a mass ratio of 1: 4, and the mixture was stirred in ethanol at room temperature for 15 minutes, and then at room temperature. Drying under reduced pressure of 5 Torr for 12 hours. The treated mixture was heat-treated at 800 ° C. for 2 hours under a nitrogen stream of 200 ml / min using a tubular furnace to obtain an electrode catalyst (A-1).
[Create electrode]
As the electrode, a ring disk electrode in which the disk part is glassy carbon (6.0 mmφ) and the ring part is Pt (ring inner diameter 7.3 mm, ring outer diameter 9.3 mm) was used.
To a sample bottle containing 1 mg of the electrode catalyst (A-1), 0.5 ml of a total fluorinated ionomer solution having a sulfonic acid group diluted to 1/50 with methanol (Aldrich 5 mass% Nafion solution) was added. Thereafter, a dispersion treatment was performed with ultrasonic waves. 10 μL of the obtained suspension was dropped on the disk part of the electrode, and then dried at room temperature for 30 minutes to obtain a measurement electrode.
[Evaluation of oxygen reduction ability by rotating ring disk electrode]
By rotating the electrode produced above, the current value of the oxygen reduction reaction at that time was evaluated. The measurement is performed at room temperature in a nitrogen atmosphere and an oxygen atmosphere, and the current value obtained by measurement in the nitrogen atmosphere is subtracted from the current value obtained in the measurement in the oxygen atmosphere. Did. The measurement apparatus and measurement conditions are as follows.

Measuring device Rotating ring disk electrode device: Day thickness measurement RRDE-1
Dual potentio galvanostat: thickness measurement model DPGS-1
Function generator: Toho Giken model FG-02
Measurement conditions Test solution: 0.05 mol / L sulfuric acid aqueous solution Reference electrode: Reversible hydrogen electrode (RHE)
Counter electrode: platinum wire Disk potential sweep rate: 5 mV / s, ring potential 1.4 V vs RHE
Electrode rotation speed: 600 rpm

  Table 1 shows the catalytic activity for oxygen reduction of the electrode catalyst (A-1). The catalytic activity is shown as mass activity obtained by dividing the current density at 0.6 V with respect to the reversible hydrogen electrode by the amount of metal supported per unit area on the electrode. It can be seen that the heat-treated product of the mononuclear metal complex (A) is superior in oxygen reducing ability as compared with Comparative Example 1 below.

  In the said operation, the mononuclear metal complex (A) was replaced with the mononuclear metal complex (B), and the electrode catalyst (B) was prepared. The oxygen reduction ability was evaluated according to the above method. The results are shown in Table 1.

Comparative Example 1
The mononuclear metal complex (C) and graphite powder (Aldrich; 1-2 μm) are mixed at a weight ratio of 1: 4, and the mixture is heat-treated at 600 ° C. for 2 hours in a nitrogen stream using a tubular furnace. Catalyst (C) was obtained. The oxygen reduction ability of the electrode catalyst (C) was evaluated according to the method described in Example 1. The results are shown in Table 1. The catalytic activity of the electrocatalyst (C) prepared using the mononuclear metal complex (C) having no aromatic heterocycle is significantly lower than that of the electrocatalyst (A-1) and the electrocatalyst (B). I understand.

Example 2 (Calculation by density functional)
In the mononuclear metal complex (A), mononuclear metal complex (B), and mononuclear metal complex (C) used in Example 1, one oxygen molecule is adsorbed to form an oxygen molecule-adsorbed mononuclear metal complex. The Mulliken charges of two oxygen atoms constituting one oxygen molecule were calculated using a density functional. Table 2 shows the absolute value of the difference between the Mulliken charges of the two oxygen atoms and the sum of the two charges.

Example 3 (Evaluation of hydrogen oxidation ability)
[Preparation of electrode catalyst]
The electrode catalyst (A-2) was prepared by mixing the mononuclear metal complex (A) and the carbon support (Ketjen Black EC300J, manufactured by Lion Corporation) at a mass ratio of 1: 4.
[Create electrode]
As the electrode, a ring disk electrode in which the disk part is glassy carbon (6.0 mmφ) and the ring part is Pt (ring inner diameter 7.3 mm, ring outer diameter 9.3 mm) was used. 0.5 ml of a fully fluorinated ionomer solution having a sulfonic acid group diluted to 1/50 with methanol (Aldrich, 5% by mass Nafion solution) was added to a sample bottle containing 1 mg of an electrode catalyst, followed by ultrasonication. Distributed processing was performed. After applying 10 μL of the obtained suspension to the disk part of the electrode, the electrode for measurement was obtained by drying at room temperature for 30 minutes.
[Evaluation of hydrogen oxidation ability by rotating ring disk electrode]
Measurement is performed at room temperature in a nitrogen atmosphere and a hydrogen atmosphere, and a value obtained by subtracting a current value obtained by measurement in a nitrogen atmosphere from a current value obtained by measurement in a hydrogen atmosphere at 0.1 V is subjected to hydrogen oxidation. Current value. The apparatus and measurement conditions are as follows.

Measuring device Rotating ring disk electrode device: Day thickness measurement RRDE-1
Dual Potentiogalvanostat: Day thickness measurement DPGS-1
Function generator: Toho Giken model FG-02
Measurement method Linear sweep voltammetry Measurement conditions Test solution: 0.10 mol / L perchloric acid aqueous solution Reference electrode: Reversible hydrogen electrode (RHE)
Counter electrode: platinum wire Disk potential sweep rate: 5 mV / s, ring potential 1.4 V vs RHE
Electrode rotation speed: 300rpm

  Table 3 shows the mass activity of hydrogen oxidation of the electrode catalyst (A-2). From Table 3, it can be seen that the electrode catalyst (A-2) has hydrogen oxidizing ability. Here, the mass activity is a value obtained by dividing the current value at a potential of 0.1 V with respect to the reversible hydrogen electrode by the electrode area and then dividing by the amount of metal supported per electrode unit area.

  In the above operation, the mononuclear metal complex (A) is replaced with the mononuclear metal complex (D), the mononuclear metal complex (E), and the mononuclear metal complex (F), and the same operation is performed, respectively. Was evaluated. In addition, about the mononuclear metal complex (E), the electrode catalyst (F-1) which mixed the mononuclear metal complex (E) and the carbon support | carrier (Ketjen Black EC300J, the Lion company make) by mass ratio of 1: 4, And the electrode catalyst (F-2) which performed the heat processing for 2 hours at 500 degreeC in the tubular furnace was prepared, and hydrogen oxidation ability was evaluated, respectively. The results are shown in Table 3.

Claims (8)

  A fuel cell electrode catalyst using a mononuclear metal complex having an organic compound having two or more phenol rings and three or more aromatic heterocycles as a ligand. The fuel cell electrode catalyst according to claim 1, wherein the mononuclear metal complex is represented by the following formula (I).

(In the formula, R ¹ is a hydrogen atom or a substituent, and two adjacent R ^{1 s} may be linked to each other, and a plurality of R ¹ may be the same or different from each other. Q ¹ Is a divalent organic group having at least one aromatic heterocycle, T ¹ is a monovalent organic group having at least one aromatic heterocycle, and two T ¹ are the same or different from each other M represents a transition metal atom, X represents a counter ion or neutral molecule that electrically neutralizes the metal complex, n represents the number of X in the complex, and is 0 or more. And when there are a plurality of X, they may be the same as or different from each other.) 3. The fuel cell electrode catalyst according to claim 2, wherein the acid dissociation constant pKa of the conjugate acid of the aromatic heterocyclic ring constituting T ¹ of the formula (I) is −2.0 or more.   When the mononuclear metal complex adsorbs one oxygen molecule to the mononuclear metal complex, and the Mulliken charges of two oxygen atoms constituting the one oxygen molecule are calculated by a density functional method, the two oxygen atoms The fuel cell electrode catalyst according to any one of claims 1 to 3, wherein the absolute value of the difference in the Mulliken charge of the atoms is 0.020 to 0.062.   When the mononuclear metal complex adsorbs one oxygen molecule to the mononuclear metal complex, and the Mulliken charges of two oxygen atoms constituting the one oxygen molecule are calculated by a density functional method, the two oxygen atoms The fuel cell electrode catalyst according to any one of claims 1 to 4, wherein the sum of Mulliken charges of atoms is -0.25 or more.   An electrode complex for a fuel cell obtained by heating the mononuclear metal complex according to any one of claims 1 to 5 at a temperature of 250 ° C to 1500 ° C.   A fuel cell electrode catalyst comprising a mononuclear metal complex mixture comprising the mononuclear metal complex according to any one of claims 1 to 5 and a carbon support and / or a conductive polymer.   A mononuclear metal complex mixture comprising the mononuclear metal complex according to any one of claims 1 to 5 and a carbon support and / or a conductive polymer is obtained by heating at a temperature of 250 ° C to 1500 ° C. A fuel cell electrode catalyst.