JP5692701B2 - Catalysts for electrochemical oxidation of hydrides - Google Patents

Description

  The present invention relates to a catalyst for electrochemical oxidation of hydride and its use.

  In recent years, hydrogen has been considered promising as a new energy source due to environmental problems and energy problems. For example, the development of hydrogen automobiles that use hydrogen directly as fuel and fuel cells that use hydrogen are being developed. The fuel cell has excellent advantages such as small size, high power generation efficiency, no generation of noise and vibration, and use of waste heat.

  When hydrogen is used as an energy source, it is necessary to supply hydrogen as a fuel safely and stably. A method for supplying hydrogen directly as compressed hydrogen or liquid hydrogen, or a hydrogen storage material such as a hydrogen storage alloy. Various methods have been proposed, such as a method for storing and supplying hydrogen by using hydrogen and a method for supplying hydrogen by steam reforming methanol or hydrocarbon.

  However, these methods can be used for production on a factory scale or generation of hydrogen to the extent that they can be used in laboratories, but the required amount of hydrogen fuel can be continuously supplied, and downsizing is required. It is unsuitable as a hydrogen supply method for automobile fuel cells; portable fuel cells for mobile phones, personal computers, and the like.

On the other hand, attempts have been made to use various metal hydrides such as LiAlH ₄ and NaBH ₄ as a hydrogen generating material. In particular, many current portable hydrogen generators employ a method of generating hydrogen by adding a catalyst containing a noble metal in a metallic state such as platinum-supported carbon to a hydride. However, in the method using a hydride oxidation catalyst composed of a noble metal in a metal state, since the hydride self-decomposition reaction proceeds in an aqueous solution, it is difficult to control the hydrogen generation amount, the hydrogen generation rate, and the like. There is also a problem that the amount of noble metal used is large because noble metal is used in a bulk metal state (see Non-Patent Document 1 below).

  In addition, development of a direct fuel cell that uses metal hydride as a direct fuel without generating hydrogen from these metal hydrides is also underway (see Non-Patent Documents 2 and 3 below). However, since these fuel cells use a noble metal in a metallic state on the anode side, there is a problem that hydrides decompose during non-power generation, and some hydrides decompose without being oxidized electrochemically even during power generation. . There is also a problem that the amount of noble metal used is increased on the anode side.

Fuel Process. Technol. 87 (2006) 811-819 Electrochem. Commun. 10 (2008) 100-102 J. Power Sources 176 (2008) 287-292

  The present invention has been made in view of the current state of the prior art described above, and its main purpose is a catalyst effective for the oxidation reaction of hydride, particularly when hydride is used as a hydrogen generation source. When generating electricity using hydride or hydride as a direct fuel, it is possible to solve the problems associated with conventional noble metal catalysts and to provide a new low-cost catalyst.

  The present inventor has intensively studied to achieve the above-described object. As a result, the complex containing a specific transition metal atom is very cheap compared to a catalyst containing a conventional noble metal component, and has an excellent activity as an electrochemical oxidation catalyst for various hydrides. And having a very low activity in the hydride self-decomposition reaction. The metal complex can exhibit excellent performance when used as an anode catalyst for a hydrogen generator or a direct borohydride fuel cell. For example, an electrochemical oxidation reaction of a hydride using the metal complex In combination with the hydrogen generation reaction at the cathode makes it easy to control the rate and amount of hydrogen generation, and to make effective use of the electrochemical energy generated during the hydrogen generation reaction. The headline and here came to complete the present invention.

That is, the present invention provides the following catalyst for electrochemical oxidation of hydride and use thereof.
1. A catalyst for electrochemical oxidation of a hydride comprising a metal complex containing cobalt, iron or copper as a metal component and containing a nitrogen-containing polycyclic compound as a ligand.
2. Item 2. The catalyst for electrochemical oxidation of a hydride according to Item 1, wherein the ligand is a porphyrin compound, a phthalocyanine compound, or a salen compound.
3. Item 3. The catalyst for electrochemical oxidation of a hydride according to Item 1 or 2, wherein the metal complex is supported on a conductive support.
4). Item 4. The catalyst for electrochemical oxidation of a hydride according to any one of Items 1 to 3, wherein the hydride is an alkali metal borohydride compound.
5. 5. An anode for a direct fuel cell using a borohydride compound as a fuel, comprising the catalyst according to any one of Items 1 to 4 as an anode electrode catalyst.
6). An anode side electrode part to which a solution containing a hydride and a hydroxide is supplied;
A cathode-side electrode portion that is arranged opposite to the anode-side electrode portion and generates hydrogen by a proton reduction reaction;
A hydrogen generator comprising an ion permeable diaphragm disposed between the anode side electrode part and the cathode side electrode part,
A hydrogen generator comprising the catalyst according to any one of Items 1 to 4 as a catalyst for the anode side electrode.
7). 7. The hydrogen generator according to item 6, wherein the anode electrode catalyst is a catalyst having an anode electrode potential lower than the cathode electrode potential in an open circuit.

  Hereinafter, the catalyst for electrochemical oxidation of hydride of the present invention will be described in detail.

Catalyst for Electrochemical Oxidation of Hydride The catalyst for electrochemical oxidation of hydride of the present invention is a metal complex containing cobalt, iron or copper as a metal component and a nitrogen-containing polycyclic compound as a ligand. is there.

  Among these, examples of the nitrogen-containing polycyclic compound used as the ligand include porphyrin compounds, phthalocyanine compounds, and salen compounds.

  By using these specific metal complexes as catalysts, it becomes possible to oxidize hydrides with a low overvoltage. Further, since the metal complex has low activity for chemical decomposition reaction of hydride, the decomposition reaction of hydride is extremely slow when the electrode provided with the metal complex is not connected to the cathode electrode.

  In particular, the metal complex contains relatively inexpensive cobalt, iron or copper as a metal component, and these metal components are used not as a metal in a bulk state but as a metal complex containing the metal component. For this reason, it is a cheap catalyst compared with the catalyst which uses the conventional noble metal component as an active ingredient, and also has sufficient activity with respect to the electrochemical oxidation reaction of hydride.

  In the present invention, any metal complex containing the above-mentioned specific transition metal component and containing a nitrogen-containing polycyclic compound as a ligand can be used without any particular limitation. Is not particularly limited.

  In particular, a metal complex containing a porphyrin compound as a ligand is preferable in that the overvoltage of the hydride electrochemical oxidation reaction is low.

  Hereafter, a preferable specific example is shown about the metal complex which is an active ingredient of the catalyst of this invention.

  (1) Chemical formula:

(Wherein R _{1 to} R ₁₂ are the same or different and each represents an alkyl group, an aryl group which may have a substituent, a hydrogen atom or a halogen atom, and M represents cobalt, iron or copper. The metal porphyrin complex represented by this.

  In the above chemical formula, the central metal element represented by M is cobalt, iron or copper, and iron is particularly preferable in that it is inexpensive.

R _{1 to} R ₁₂ are the same or different and each represents an alkyl group, an aryl group that may have a substituent, a hydrogen atom, or a halogen atom. Among these, as an alkyl group, methyl, ethyl, isopropyl, n-propyl, t-butyl, sec-butyl, n-butyl, isobutyl, n-pentyl, etc. A branched lower alkyl group is preferred. Further, as the halogen atom, fluorine, chlorine, bromine and the like are preferable. As the aryl group which may have a substituent, a phenyl group, a phenyl group having a substituent, a pyridyl group, a pyridyl group having a substituent, and the like are preferable.

Among these, when R ₁ , R ₄ , R _7, and R ₁₀ are all aryl groups that may have a substituent, the meso position is chemically protected, so that the oxidation reaction and the like are prevented. Increases stability.

Among the aryl groups having a substituent, examples of the pyridyl group having a substituent include a 1-methylpyridyl group. Examples of the substituent in the phenyl group having a substituent include a lower alkoxy group, a lower alkyl group, a halogen atom, —SO ₃ M ¹ (wherein M ¹ is a hydrogen atom, an alkali metal, or —NH ₄ ), —COOM. ² (wherein M ² is a hydrogen atom, an alkali metal, —NH ₄ or an alkyl group), —OCH ₂ —COOM ³ (wherein M ³ is a hydrogen atom, an alkali metal, —NH ₄ or an alkyl group) And the like.

  Among these, as a phenyl group having a lower alkoxy group as a substituent, a para-methoxyphenyl group and the like, and as a phenyl group having a lower alkyl group as a substituent, a para-methylphenyl group, 2,4,6-trimethyl Examples of the phenyl group having a halogen atom as a substituent such as a phenyl group include a pentafluorophenyl group.

Among the substituents of the phenyl group, the _-SO 3 ^{M 1, M 1} is a hydrogen atom, an alkali metal or -NH _4. Among these, examples of the alkali metal include K and Na. Among the substituents of the phenyl group, in —COOM ² , M ² is a hydrogen atom, an alkali metal, —NH ₄ or an alkyl group. Among these, examples of the alkali metal include K and Na. Examples of the alkyl group include the same groups as those described above. Among the substituents of the phenyl group, in —OCH ₂ —COOM ³ , M ³ is a hydrogen atom, an alkali metal, —NH ₄ or an alkyl group. Among these, examples of the alkali metal include K and Na. Examples of the alkyl group include the same groups as those described above.

Substituents such as —SO ₃ M ¹ , —COOM ² and —OCH ₂ —COOM ³ can be substituted at the 4-position of the phenyl group, for example, but are not limited thereto.

As a representative example of the porphyrin complex represented by the above chemical formula, R ₁ , R ₄ , R ₇ and R ₁₀ are phenyl groups that may have a substituent, and R _2, R ₃ , R ₅ , R ₆ , A tetraphenylporphyrin complex in which R ₈ , R ₉ , R ₁₁ and R ₁₂ are hydrogen atoms; R ₁ , R ₄ , R ₇ and R ₁₀ are hydrogen atoms, and R _2, R ₃ , R ₅ , R ₆ , R ₈ , R ₉ , R ₁₁ and R ₁₂ are octaalkylporphyrin complexes in which a lower alkyl group is exemplified.

    (2) Chemical formula

(Wherein R _{1 to} R ₈ are the same or different and each represents a hydrogen atom, an alkyl group, a hydroxyalkyl group, an alkenyl group, a group: —SO ₃ M ₁ (wherein M ₁ represents a hydrogen atom, an alkali A metal or —NH ₄ ), or a group: —R ₉ —COOM ₂ (wherein R ₉ is a linear or branched alkylene group, and M ₂ is a hydrogen atom, an alkali metal or an alkyl group) Or at least one combination of R ₁ and R ₂ , R ₃ and R ₄ , R ₅ and R ₆ , R ₇ and R ₈ is bonded to each other, and these groups are bonded to each other. An aromatic ring which may have a substituent may be formed together with the carbon atom to be used, and M represents cobalt, iron or copper, provided that at least one of R _{1 to} R ₈ is a group: —R ₉ -COOM ₂ ).

  In the above chemical formula, the central metal element represented by M is cobalt, iron or copper, and iron is particularly preferable in that it is inexpensive.

  In the above chemical formula, the alkyl group is linear or branched having about 1 to 5 carbon atoms such as methyl, ethyl, isopropyl, n-propyl, t-butyl, sec-butyl, n-butyl, isobutyl, n-pentyl and the like. A chain-like lower alkyl group is preferred.

  As the alkyl group portion of the hydroxyalkyl group, a straight chain having about 1 to 5 carbon atoms such as methyl, ethyl, isopropyl, n-propyl, t-butyl, sec-butyl, n-butyl, isobutyl, n-pentyl or the like A branched lower alkyl group can be exemplified. The hydroxy group can be substituted on any carbon atom of the alkyl group.

  Examples of the alkenyl group include linear or branched alkenyl groups having 2 to 6 carbon atoms such as vinyl, allyl, 2-butenyl, 3-butenyl, 1-methylallyl, 2-pentenyl, 2-hexenyl and the like. Can do.

In the group: —SO ₃ M ₁ , M ₁ is a hydrogen atom, an alkali metal, or —NH ₄ . Among these, examples of the alkali metal include K and Na.

In the group: —R ₉ —COOM ₂ , as the alkylene group represented by R ₉ , for example, methylene, ethylene, trimethylene, 2-methyltrimethylene, 2,2-dimethyltrimethylene, 1-methyltrimethylene, methylmethylene C1-C6 linear or branched alkylene groups such as ethylmethylene, tetramethylene, pentamethylene and hexamethylene groups. The alkyl group and alkali metal represented by M ₂ are the same as those described above.

In the metalloporphyrin complex represented by the above chemical formula, a compound in which two or more of R _{1 to} R ₈ are a group: —R ₉ —COOM ₂ has a particularly high activity for an electrochemical oxidation reaction of a hydride. It is what has.

  (3) Chemical formula

(Wherein R _{1 to} R ₁₆ are the same or different and each represents a hydrogen atom, an alkyl group, an alkoxyl group, a halogen atom or a sulfonic acid group, or R ₂ and R ₃ , R ₆ and R _7). , R ₁₀ and R ₁₁ , and each combination of R ₁₄ and R ₁₅ are bonded to each other to form an aromatic ring which may have a substituent together with the carbon atom to which these groups are bonded. And M represents cobalt, iron, or copper.) A metal phthalocyanine complex represented by:

  In the above chemical formula, the central metal element represented by M is cobalt, iron or copper, and iron is preferable in that it is inexpensive.

In the above chemical formula, R _{1 to} R ₁₆ are the same or different and each represents a hydrogen atom, an alkyl group, an alkoxyl group, a halogen atom, or a sulfonic acid group. Further, among these, at least one of each combination of R ₂ and R ₃ , R ₆ and R ₇ , R ₁₀ and R ₁₁ , R ₁₄ and R ₁₅ is bonded to each other, and these groups are bonded. You may form the aromatic ring which may have a substituent with a carbon atom.

  Among these, as an alkyl group, methyl, ethyl, isopropyl, n-propyl, t-butyl, sec-butyl, n-butyl, isobutyl, n-pentyl, etc. A branched lower alkyl group is preferred. Examples of the alkoxy group include straight chain or branched chains having 1 to 6 carbon atoms such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, tert-butoxy, n-pentyloxy, n-hexyloxy group, and the like. An alkoxyl group is preferred. Further, as the halogen atom, fluorine, chlorine, bromine and the like are preferable.

Among the metal phthalocyanine complexes represented by the above chemical formula, for example, a compound in which R _{1 to} R ₁₆ are all hydrogen atoms has high activity for an electrochemical oxidation reaction of a hydride.

Each combination of R ₂ and R ₃ , R ₆ and R ₇ , R ₁₀ and R ₁₁ , R ₁₄ and R ₁₅ is bonded to each other, and has a substituent together with the carbon atom to which these groups are bonded. As an aromatic ring-containing compound, the following chemical formula

The compound represented by these can be illustrated. In the above chemical formula, R _{17 to} R ₃₂ are the same or different and each represents a hydrogen atom, an alkyl group, an alkoxyl group, a halogen atom, or a sulfonic acid group. Specific examples of each of these groups are the same as R _{1 to} R ₁₆ .

  (4) Chemical formula:

A metal-salen complex represented by the formula (wherein M is cobalt, iron or copper).

  In the above chemical formula, the central metal element represented by M is cobalt, iron or copper, and iron is particularly preferable in that it is inexpensive.

  In the salen complex described above, an arbitrary substituent may be present on the salen ring.

Method for Producing Metal Complex The metal complex described above can be produced , for example, by dissolving a compound serving as a ligand of the target complex and the metal compound in a solvent and heating.

  For example, as a copper compound, a compound containing a monovalent or divalent copper element, as a cobalt compound, a compound containing a divalent or trivalent cobalt element, as an iron compound, as a divalent or trivalent iron A compound containing an element can be used. As the solvent, a solvent capable of dissolving the above-described ligand compound and metal compound may be used. For example, ethanol, dimethylformamide, or the like can be used. The heating temperature may be, for example, the reflux temperature of the solvent used.

Supported Catalyst The above-described metal complex can have a high catalytic activity for an electrochemical oxidation reaction of a hydride by being supported on a conductive support.

  The conductive carrier is not particularly limited, and for example, various carriers conventionally used as catalyst carriers for polymer electrolyte fuel cells can be used. Specific examples of such a carrier include carbonaceous materials such as carbon black, activated carbon, and graphite. Among these, carbon black is a particularly preferable substance as a conductive carrier because it is excellent in conductivity and has a large specific surface area.

The shape of the conductive carrier is not particularly limited, and for example, a conductive carrier having an average particle diameter of about 0.1 to 100 μm, preferably about 1 to 10 μm can be used. Further, when carbon black is used, for example, is preferably one in the range BET specific surface area of about 100~800m ² / g, more is intended to be within the range of about 200 to 300 [m ² / g preferable. As a specific example of such a carbon black, those commercially available under the trade name Vulcan XC-72R (Cabot) can be used.

  As a method for supporting the conductive carrier, for example, a known method such as a dissolution drying method or a gas phase method can be applied.

  For example, in the dissolution drying method, a metal complex is dissolved in an organic solvent, and a conductive carrier is added to this solution. For example, the metal complex is adsorbed on the carrier by stirring for several hours, and then the organic solvent is dried. Just do it. In addition, when a large amount of metal complex is contained in the organic solvent, the metal complex that is not adsorbed on the conductive support is removed by filtering after adsorbing the metal complex on the conductive support until equilibrium is reached. Thus, only the metal complex interacting with the support can be left on the surface of the support.

  In this method, any organic solvent can be used without particular limitation as long as it can dissolve the metal complex. For example, chlorinated hydrocarbons such as dichloromethane and chloroform and lower alcohols such as ethanol can be preferably used.

  If the dispersion obtained by filtration is further washed with an organic solvent until the washing liquid becomes transparent, the metal complex having a weak interaction with the conductive carrier can be washed away and firmly adsorbed on the conductive carrier. It is possible to obtain a highly active catalyst containing only the metal complex.

  In the case of carrying by a vapor phase method, for example, a known method such as a plasma vapor deposition method, a CVD method, or a heating vapor deposition method can be adopted.

  The amount of the metal complex to be supported on the conductive carrier is not particularly limited. For example, it is preferable to carry about 10 μmol to 1000 μmol of the metal complex with respect to 1 g of the conductive carrier, and about 20 μmol to 100 μmol. Is more preferable.

Use of the catalyst of the present invention Any of the metal complexes described above has excellent activity as a catalyst for electrochemical oxidation reaction of hydride.

The hydride to be subjected to the electrochemical oxidation reaction by the catalyst of the present invention is not particularly limited. For example, a compound represented by the general formula: X (YH _4-n Z _n ) can be used. . In the above general formula, X is an alkali metal, NH ₄ , or M _1/2 (wherein M is an alkaline earth metal), Y is B, Al or Ga, and Z is a halogen atom or a single atom. And n is an integer of 0 to 3. Examples of the alkali metal include Li. Na, K, Rb, and Cs. Examples of the alkaline earth metal include Mg, Ca, Sr, and Ba. Examples of the halogen atom include F, Cl, Br, and I. Etc. can be illustrated. Examples of the monovalent hydrocarbon group include a linear or branched alkyl group having about 1 to 6 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, Isobutyl, tert-butyl, sec-butyl, n-pentyl, 1-ethylpropyl, isopentyl, neopentyl, n-hexyl, 1,2,2-trimethylpropyl, 3,3-dimethylbutyl, 2-ethylbutyl, isohexyl, 3 -A methylpentyl group etc. can be illustrated.

Among these hydrides, alkali metal borohydride compounds such as LiBH ₄ , NaBH ₄ and KBH ₄ are particularly preferable.

  By using the catalyst of the present invention, the hydride electrochemical oxidation reaction proceeds at a low overvoltage. For example, when an alkali metal borohydride compound is used, the following reaction proceeds.

BH ₄ ⁻ + 8HO ⁻ → BO ₂ ⁻ + 6H ₂ O + 8e ⁻
The electrochemical oxidation reaction of the hydride can proceed with high selectivity by setting it to a predetermined potential in a state where the hydride is in contact with the catalyst. For example, the electrochemical oxidation reaction can be allowed to proceed by immersing the electrode provided with the catalyst of the present invention in an aqueous solution containing an alkaline hydride having a pH of about 12 or more and setting the electrode at a predetermined potential. The specific potential in this case cannot be defined unconditionally because it varies depending on the type of metal complex to be used, the type of hydride, the state of the solution, etc. As a reference for AgCl / KCl (saturated) electrode), a metal complex having a nitrogen-containing polycyclic compound (porphyrin, phthalocyanine, salen, etc.) as a ligand is preferably about -0.7 V to -0.4 V, In particular, it is more preferably about −0.7 V to −0.6 V.

  The catalyst of the present invention can be used for various applications utilizing the electrical oxidation reaction of hydride utilizing the above-described excellent characteristics. For example, it can be effectively used for applications such as an anode catalyst in a direct borohydride fuel cell using hydride as a fuel and an anode catalyst in a hydrogen generator using hydride as a raw material. Hereinafter, these uses will be described.

(1) Direct-type borohydride fuel cell The catalyst of the present invention can be effectively used as an anode electrode catalyst of a direct-type borohydride fuel cell. The structure of the direct borohydride fuel cell using the catalyst of the present invention is not particularly limited as long as it is a direct fuel cell using a borohydride compound as a fuel. For example, an aqueous solution of a borohydride compound such as NaBH ₄ described in “Electrochem. Commun. 10 (2008) 100-102”, “J. Power Sources, 176 (2008) 287-292”, etc. is used as a fuel. It can be used as an anode electrode catalyst of a direct borohydride fuel cell using an anion exchange membrane or an alkaline solution as an electrolyte and a platinum group metal, gold, silver or the like as a cathode electrode catalyst.

  By using the catalyst of the present invention as an anode electrode catalyst of a direct borohydride fuel cell, it is possible to suppress the decomposition of the fuel during non-power generation and to take out electricity from a high voltage.

(2) Hydrogen generator The catalyst of the present invention uses an ion permeable membrane for an anode reaction including an oxidation reaction of a hydride in a solution containing a hydride and a hydroxide and a cathode reaction including a hydrogen generation reaction by reduction of protons. It can be used as an anode catalyst in a method for generating hydrogen by generating the catalyst.

  A hydrogen generation apparatus using the above-described hydrogen generation method includes, for example, an anode side electrode portion to which a solution containing a hydride and a hydroxide is supplied, and a cathode side electrode that is disposed opposite to the anode side electrode portion and generates hydrogen. And an ion permeable diaphragm disposed between the anode side electrode part and the cathode side electrode part, wherein the catalyst of the present invention is used as an anode catalyst in the anode side electrode part. is there.

  Hereinafter, a hydrogen generation method using the catalyst of the present invention will be described with reference to FIG. 1 showing a schematic configuration of one embodiment of the above-described hydrogen generation apparatus.

  A hydrogen generator 1 shown in FIG. 1 includes an anode side electrode 2, a cathode side electrode 3, and an ion exchangeable diaphragm 4 as main components. A solution containing a hydride and a hydroxide is supplied to the anode side electrode 2 from the anode side raw material inlet 6 as a raw material solution.

As the hydroxide, for example, a compound represented by the general formula: AOH can be used. In the above general formula, A is an alkali metal, NH ₄ , or M _1/2 (wherein M is an alkaline earth metal). Examples of the alkali metal include Li, Na, K, Rb, and Cs, and examples of the alkaline earth metal include Mg, Ca, Sr, and Ba. Of these hydroxides, alkali metal hydroxides such as LiOH, NaOH, and KOH are particularly preferable.

In a solution containing hydride and hydroxide, as a solvent, hydride: X (YH _4-n Z _n ) can be ionically dissociated into X ⁺ and (YH _4-n Z _n ) ⁻ in the solution. Any solvent can be used without particular limitation. As such a solvent, in addition to water, a non-aqueous solvent having a high Lewis basicity, a low Lewis acidity, and a high relative dielectric constant can be used. Examples of such nonaqueous solvents include diethyl ether, dimethoxyethane, diethoxyethane, diglyme, triglyme, tetraglyme, tetrahydrofuran, methyltetrahydrofuran, dioxane, dioxolane, tetramethylpyran, and other ethers, carbon disulfide, methyl acetate, γ-Butyllactone, methyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, acetone, formamide, methylformamide, dimethylformamide, acetamide, methylacetamide, dimethylacetamide, ethylenediamine, methylpyrrolidone, pyridine, aniline, N-methylpyrrolidone, tetra Methylurea, tetramethylguanidine, acetonitrile, nitromethane, dimethylsulfoxide, sulfolane, triethyl phosphate, hexamethylphosphorus Triamide, ammonia and the like. Preferred non-aqueous solvents are tetrahydrofuran, acetonitrile, dimethyl sulfoxide, dimethylacetamide, methylpyrrolidone, pyridine and the like.

  The concentration of hydride in the solution containing hydride and hydroxide is not particularly limited, but is preferably about 0.0001 to 30 mol / L, and more preferably about 0.001 to 10 mol / L.

  Further, the hydroxide concentration is preferably about 0.0001 to 20 mol / L, and more preferably about 0.01 to 4 mol / L.

By bringing the solution containing the hydride and hydroxide into contact with the anode side electrode, an oxidation reaction of hydride ions existing in the solution proceeds on the surface of the anode side electrode. This produces an oxidation product of hydride ions and water. For example, when a borohydride compound is used as a hydride, an anodic reaction proceeds by the following reaction, and hydride ions: BH ₄ ⁻ are oxidized.

Anode reaction: BH ₄ ⁻ + 8OH ⁻ → BO ₂ ⁻ + 6H ₂ O + 8e ⁻
The reaction temperature of the anodic reaction is not particularly limited, and the reaction can usually proceed at room temperature.

The amount of catalyst supported in the anode, for example, be a 0.1 to 5.0 mg / cm ² or so, it is preferable to 0.1-3.0 mg / cm ² or so.

  Electrons generated by the anode reaction pass through the external circuit 5 and are supplied to the cathode side electrode 3, and the following cathode reaction including hydrogen generation occurs on the surface of the cathode side electrode 3.

The cathode ^{_{reaction: 8H 2 O + 8e - →}} 4H 2 + 8 OH -
The reaction temperature of the cathode reaction is not particularly limited, and the reaction can usually proceed at room temperature.

  In the cathode side electrode 3, for example, by supplying water from the cathode side raw material inlet 8, the above-described cathode reaction can proceed. In this case, water may be supplied directly, or a humidified inert gas may be supplied. Even when water is not supplied from the cathode side raw material inlet 8, when water contained in the anode raw material or water generated by the anode reaction moves through the ion permeable diaphragm and reaches the cathode side electrode 3, The cathode reaction described above can proceed. Hydrogen generated on the surface of the cathode side electrode 3 is recovered from, for example, a hydrogen outlet 9 installed in the cathode side electrode portion. Further, hydroxide ions generated at the cathode side electrode 3 pass through the ion permeable diaphragm and move to the anode side raw material solution, or can be used again for the anode reaction by mixing with the raw material solution. . This makes it possible to proceed the reaction without supplying new hydroxide from the outside.

  The cathode side electrode 3 is not particularly limited. For example, a porous electrode in which a catalyst is supported on a carrier can be used.

  For example, the cathode side electrode 3 is provided opposite to the anode side electrode 2 so as to be in contact with the other surface of the ion permeable diaphragm 4.

  The catalyst used in the cathode-side electrode 3 may be any catalyst that has activity for the hydrogen generation reaction by proton reduction. For example, a fourth catalyst such as Ru, Rh, Pd, Ag, Os, Ir, Pt, or Au may be used. Or 5 period group 8-11 metal can be mentioned, Pt black is especially preferable.

Amount of catalyst supported in the cathode 3 is, for example, be a 0.1 to 5.0 mg / cm ² or so, it is preferable to 0.1-3.0 mg / cm ² or so.

As the ion permeable diaphragm 4, an anion permeable or cation permeable diaphragm can be used. When an anion permeable diaphragm is used, OH ⁻ ions generated by the cathode reaction pass through the anion permeable diaphragm 4 and move to the anode side electrode portion.

  In this case, the total reaction combined with the anode reaction described above is as follows.

Total reaction: BH ₄ ⁻ + 2H ₂ O → BO ₂ ⁻ + 4H ₂
As the ion permeable diaphragm 4 disposed between the anode side electrode 2 and the cathode side electrode 3 described above, for example, an anion permeation capable of passing cations dissociated from OH ⁻ ions or hydrides generated by the cathode reaction is allowed. An permeable membrane or a cation permeable membrane can be used.

As the anion permeable diaphragm, it is preferable to use a diaphragm that can permeate OH ⁻ ions generated by the anode reaction but does not permeate the hydride anion supplied to the anode electrode portion. This prevents the hydride anion from being hydrolyzed at the cathode electrode surface. As such an anion permeable membrane, for example, a trade name: Neoceptor AMX (Astom Co., Ltd.) membrane or the like can be used.

  Even when a cation permeable membrane is used, the hydride anion supplied to the anode electrode portion does not move to the cathode electrode portion, and the hydride anion is prevented from being hydrolyzed on the cathode electrode surface. . As the cation permeable membrane, a cation exchange type solid polymer electrolyte membrane capable of passing cations dissociated from hydride can be used. Specific examples of such a solid polymer electrolyte membrane include fluorine-based ion exchange membranes such as a perfluorocarbon sulfonic acid membrane and a perfluorocarbon carboxylic acid membrane, a polybenzimidazole membrane impregnated with phosphoric acid, a polystyrene sulfonic acid membrane, and a sulfone. Examples thereof include a styrene oxide / vinylbenzene copolymer film. Among these, a perfluorocarbon sulfonic acid membrane marketed under a trade name such as Nafion is particularly preferable.

  A glass filter having an appropriate pore size can also be used as the ion permeable diaphragm.

  In the hydrogen generator 1 described above, an anode-side raw material inlet 6 and an anode-side outlet 7 can be further provided outside the anode-side electrode 2, and a cathode-side raw material inlet 8 is generated outside the cathode-side electrode 3. A hydrogen discharge port 9 or the like can be provided. Further, a current collector can be provided outside the anode side electrode 2 in contact with the anode side electrode 2, and gas diffusion can be performed outside the cathode side electrode 3 in contact with the cathode side electrode 3. A layered current collector or the like can be provided. The structure of the hydrogen generator including these members may be the same as that of a known hydrogen generator. For example, the structure of the hydrogen generator described in JP-A-2005-71645 can be used.

  In the hydrogen generator having the structure described above, in particular, as an anode catalyst, a catalyst for electrochemical oxidation of a hydride of the present invention, that is, containing cobalt, iron or copper as a metal component, and containing a large amount of nitrogen as a ligand. It is an important feature to use a metal complex containing a cyclic compound. By using such a catalyst, the hydride can be electrode-oxidized at a low overvoltage, and efficient hydrogen generation becomes possible.

The catalyst of the present invention, (a borohydride ^{_{BH 4 - + 2 H 2 O}} → BO 2 - + reaction 4H ₂₎ chemical hydrogen generation reaction from the hydride because a very low activity against autolysis hydride There is little to promote the reaction. For this reason, when the external circuit which connects an anode pole and a cathode pole is opened, hydrogen generation by the self-decomposition of hydride can be suppressed. In addition, by closing the external circuit and adjusting the anode potential according to the type of electrolyte used, the type of anode catalyst, the type of cathode catalyst, etc., the rate of hydrogen generation reaction, the amount of hydrogen generation, etc. can be simplified. Can be controlled. That is, in the hydrogen generator having the above structure, when the potential of the anode electrode in the open circuit is lower than the potential of the cathode electrode, the hydrogen generation reaction based on the above-described reaction can be advanced by closing the external circuit. In addition, when the potential of the anode electrode in the open circuit is higher than the potential of the cathode electrode, the hydrogen generation reaction can be advanced by setting the potential of the anode electrode to a higher potential using an external power source. it can. At this time, it is possible to control the hydrogen generation rate, the hydrogen generation amount, and the like by adjusting the potential of the anode electrode.

  In particular, when a catalyst comprising a porphyrin complex is used as the anode catalyst, it is easy to control the amount of hydrogen generated and the generation rate because the action of causing a hydride self-decomposition reaction is low.

  When the potential of the anode electrode is lower than the potential of the cathode electrode during the open circuit, the cathode reaction and the anode reaction proceed spontaneously by closing the external circuit. In this case, the potential difference between the cathode potential and the anode potential can be acquired as electric energy simultaneously with the generation of hydrogen. For this reason, it becomes possible to obtain chemical energy and electrical energy with high energy conversion efficiency from the hydride used as a raw material. Further, there is an advantage that an external power source is unnecessary for hydrogen generation, and the structure of the apparatus can be simplified.

  The anode catalyst that can be used in a hydrogen generator having such a power generation action varies depending on the type of electrolyte used, the concentration of hydride, the type of cathode catalyst, etc. The catalyst may be selected such that is lower than the cathode reaction potential.

  Although there is no limitation in particular about the use of the hydrogen generated using the above-mentioned hydrogen generator, for example, it can be used as a fuel of a fuel cell. In this case, for example, the hydrogen discharge port 9 described above may be joined to a hydrogen supply line, and the generated hydrogen may be supplied to the fuel cell.

  The hydride electrooxidation catalyst of the present invention has the following remarkable effects.

  (1) The catalyst for electrochemical oxidation of hydride of the present invention has high activity for electrochemical oxidation reaction of hydride, and can oxidize hydride with low overvoltage. Further, the catalyst of the present invention has a very low action for promoting the self-decomposition reaction of hydride because of its low activity for chemical hydrogen generation reaction from hydride. Therefore, by using the catalyst of the present invention as an anode catalyst in a hydrogen generator using hydride as a raw material, it is easy to control the hydrogen generation rate, the hydrogen generation amount, and the like.

  (2) By using the catalyst of the present invention as an anode catalyst of a fuel cell using hydride as a direct fuel, consumption of hydride in reactions other than electrochemical reactions can be suppressed, and power generation efficiency can be improved. It becomes possible.

  (3) The catalyst of the present invention uses a relatively inexpensive specific transition metal element as a complex, and is less expensive than a catalyst using a noble metal in a bulk state or a catalyst containing a noble metal element as an active ingredient. is there.

  (4) In the hydrogen generator using the catalyst of the present invention, by selecting the catalyst so that the potential of the anode electrode is lower than the potential of the cathode electrode in the open circuit, the cathode reaction and the anode reaction are performed simultaneously with hydrogen generation. The potential difference can be acquired as electric energy.

It is a schematic block diagram which shows one Embodiment of the hydrogen generator using the catalyst of this invention. It is a graph which shows the measurement result of the linear sweep voltammetry in Examples 1-3.

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

Examples 1-10
Preparation of supported carbon catalyst Each metal complex shown in Table 1 and Table 2 below was used as a catalyst component, and each metal complex was dissolved in a solvent, and then carbon black (specific surface area 250 m ² / g, trade name: Vulcan XC 72R, manufactured by Cabot) was added in an amount of 30 mg. As the solvent, dichloromethane was used in Examples 1 to 4 and 8, dimethylformamide was used in Examples 5, 6, 9, and 10, and acetic acid was used in Example 7. The amount of the solvent used was 20 mL. The addition amount of the metal complex in each solution was 30 micromol for Example 8, and was 9 micromol for the others.

  Next, for each solution in which the carbon black was suspended, the carbon black was well dispersed using an ultrasonic cleaner, and then the solvent was distilled off by a rotary evaporator, whereby each metal complex was supported on the carbon black. .

Evaluation of catalytic activity The catalyst in which each metal complex is supported on carbon black by the above method is crushed in a mortar, and 5 mg is suspended in 0.5 mL of a mixed solvent (water: ethanol = 1: 1). After that, 5 μL of 5% Nafion solution (Aldrich) was added. This suspension was placed in an ultrasonic cleaner for 5 minutes to be well dispersed, and then 2 μL was placed on a rotating disk electrode (diameter 3 mm) and dried.

  Evaluation of the oxidation activity of the catalyst hydride was carried out using a potentiostat (ALS model 711B) manufactured by ALS. The rotational speed was controlled using a rotational speed control device (BAS RDE-1) manufactured by BAS Co., Ltd. A glassy carbon rotating disk electrode coated with a catalyst was used as a working electrode, a platinum electrode as a counter electrode, and an Ag / AgCl / KCl (sat.) Electrode as a reference electrode.

Using 0.1 M NaOH as an electrolyte, NaBH ₄ was added to 1 mM, and linear sweep voltammetry was measured while rotating the electrode at a speed of 3600 ppm.

  About the catalyst using each metal complex of Examples 1-3, a measurement result is shown in the graph of FIG.

As is clear from FIG. 2, for the catalyst supporting copper octaethylporphyrin of Example 1, an oxidation current is observed from around −0.73 V with respect to the Ag / AgCl / KCl (sat.) Electrode. In addition, with respect to the catalyst loaded with cobalt octaethylporphyrin of Example 2 and the catalyst loaded with iron octaethylporphyrin of Example 3, an oxidation current was observed from around −0.65 V. It can be seen that BH ₄ ^- is oxidized even near the potential. In these catalysts, the oxidation current rapidly increased as the potential became positive. For the catalyst of Example 1, an oxidation current of about 200 μA was obtained at around −0.4 V.

  In addition, with respect to the catalyst in which the metal complex of each Example was supported on carbon black, the current value (mA / micromole) per 1 micromole of metal at −0.5 V obtained by the above-described method was shown in Table 1 and Table 1 below. It is shown in 2.

Test example ( chemical hydrogen generation activity in the presence of NaBH ₄ )
Catalyst (Cu (OEP) in which copper octaethylporphyrin used in Example 1 was supported on carbon black in 0.5 mL of a mixed solvent (water: ethanol = 1: 1) containing 5 μL of Nafion 5% solution (Aldrich). ) / C) 0.2 mL of the suspension in which 5 mg was suspended was placed on a glassy carbon plate (effective surface area = 4.5 cm ² ) and dried to prepare a copper complex-modified electrode. Moreover, as Comparative Example 1, a suspension of platinum-supported carbon (40%, Johnson Matthey, Pt / C) was prepared by the same method (however, suspended in 0.5 mL of water), and the same method was used for glassy. It applied and dried on the carbon electrode.

  Next, the glassy carbon plate modified with Cu (OEP) / C was immersed in a 0.1 M NaOH aqueous solution containing 10 mM NaOH. After purging the solution with argon, the bottle containing this aqueous solution was sealed with a silicon stopper and allowed to stand for 180 minutes, and then hydrogen gas in the gas phase was quantified. The amount of hydrogen generated from the glassy carbon plate modified with Pt / C was also measured by the same method (however, the standing time was 17 minutes). The measurement results of the hydrogen generation rate are shown in Table 3 below.

From the above results, the catalyst of Example 1 containing copper octaethylporphyrin as an active ingredient has significantly suppressed hydrogen generation at rest compared to the platinum catalyst of Comparative Example 1, and the chemical properties of NaBH ₄ It is clear that the activity for the decomposition reaction is extremely weak.

DESCRIPTION OF SYMBOLS 1 Hydrogen generator 2 Anode side electrode 3 Cathode side electrode 4 Ion-permeable diaphragm 5 External circuit 6 Anode side raw material inlet 7 Anode side outlet 8 Cathode side raw material inlet 9 Hydrogen extraction port

Claims (5)

A catalyst for electrochemical oxidation of an alkali metal borohydride compound comprising a metal complex containing cobalt, iron or copper as a metal component and containing a porphyrin compound, phthalocyanine compound or salen compound as a ligand. The catalyst for electrochemical oxidation of an alkali metal borohydride compound according to claim 1, wherein the metal complex is supported on a conductive carrier. An anode electrode for a direct type fuel cell comprising the catalyst according to claim 1 or 2 as an anode electrode catalyst and using an alkali metal borohydride compound as a fuel. An anode side electrode portion to which a solution containing an alkali metal borohydride compound and a hydroxide is supplied;
A cathode-side electrode portion that is arranged opposite to the anode-side electrode portion and generates hydrogen by a proton reduction reaction;
A hydrogen generator comprising an ion permeable diaphragm disposed between the anode side electrode part and the cathode side electrode part,
A hydrogen generator comprising the catalyst according to claim 1 or 2 as a catalyst for the anode side electrode. 5. The hydrogen generator according to claim 4 , wherein a catalyst having an anode electrode potential lower than a cathode electrode potential in an open circuit is used as the anode electrode catalyst.

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