JP2010144206A - Method for generating hydrogen and hydrogen generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel method for generating hydrogen, which can control the amount of hydrogen to be generated, the rate of hydrogen generation and the like, while using a hydride as a raw material and using an apparatus having a relatively simple structure, and to provide a hydrogen generator which can be used for the method. <P>SOLUTION: The method for generating hydrogen is directed for causing an anode reaction including an electrochemical oxidation reaction of the hydride and a cathode reaction including a hydrogen generation reaction due to the reduction of protons in an electrolyte containing the hydride and a hydroxide, and includes using ruthenium oxide as a catalyst for the cathode. The hydrogen generator has an electrolytic tank in which the electrochemical oxidation reaction of the hydride and the electrochemical reduction reaction of the proton are caused, and the anode and the cathode which are inserted in the electrolytic tank; and includes using ruthenium oxide as the catalyst for the cathode. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hydrogen generation method and a hydrogen generation apparatus.

  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 not suitable as a hydrogen supply method for automobile-mounted 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 hydrogen compounds 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 a method using a 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).

Further, a hydrogen comprising an anode for decomposing a fuel having a standard oxidation-reduction potential of 0 or less, a cathode disposed opposite to the anode and generating hydrogen, and an electrolyte membrane disposed between the anode and the cathode A generator is also reported (see Patent Document 1 below). In this document, hydrazines such as hydrazine (NH ₂ NH ₂ ) and hydrazine (NH ₂ NH ₂ .H ₂ O), ammonia (NH ₃ ), formic acid (HCOOH) and the like are described as fuels. These fuels have a low flash point and require careful handling. In addition, ammonia and carbon monoxide are generated by a side reaction on the anode side, and these by-products have a problem that the electrode reaction on the anode side is inhibited by adsorbing to the electrode surface. Furthermore, since the fuel crosses over the electrolyte membrane, not only does the fuel oxidize at the cathode to reduce the amount of hydrogen generated, but also impurities such as ammonia, carbon monoxide and carbon dioxide are mixed in the generated hydrogen gas. There is a problem of doing.
Fuel Process. Technol. 87 (2006) 811-819 JP 2005-71645 A

  The present invention has been made in view of the current state of the prior art described above, and its main purpose is to use a hydride as a raw material, and use a device with a relatively simple structure to generate a hydrogen generation amount and a hydrogen generation rate. A novel hydrogen generation method capable of controlling the above, and a hydrogen generation apparatus that can be used in this method.

  The present inventor has intensively studied to achieve the above-described object. As a result, the inventors have found a new property which has not been known so far, that ruthenium oxide has high activity for electrochemical reduction reaction of proton and very low activity for chemical oxidation reaction of hydride. In a hydrogen generation method using an electrochemical oxidation reaction of a hydride, a substance having catalytic activity for an electrochemical oxidation reaction of a hydride is used as an anode electrode catalyst, and ruthenium oxide is used as a cathode electrode catalyst. In this case, since the natural decomposition of the hydride hardly proceeds at the cathode electrode, the solution containing the hydride and the hydroxide without distinguishing between the electrolyte solution on the anode electrode side and the electrolyte solution on the cathode electrode side. It was found that the hydrogen generation reaction can be controlled with good control by using as a common electrolyte. According to this method, since the same solution is used as the electrolyte solution on the anode electrode side and the electrolyte solution on the cathode electrode side, the electrolytic cell comprising a single chamber in which the anode electrode side and the cathode electrode side are not separated by the diaphragm Even when using a hydrogen generator, the hydrogen generation rate and hydrogen generation rate can be easily controlled by adjusting the open / closed state of the external circuit and the potential of the anode with respect to the cathode. It was found that the required amount of hydrogen can be easily obtained by using, and the present invention has been completed here.

That is, the present invention provides the following hydrogen generation method and hydrogen generation apparatus.
1. A method for generating hydrogen by causing an anode reaction including an electrochemical oxidation reaction of a hydride and a cathode reaction including a hydrogen generation reaction by reduction of protons in an electrolyte solution containing a hydride and a hydroxide, A method comprising using ruthenium oxide as a cathode electrode catalyst.
2. Item 2. The method for generating hydrogen according to Item 1, wherein the ruthenium oxide is a compound represented by a composition formula: RuO ₂ · xH ₂ O (x is a numerical value of 0 to 4).
3. The anode catalyst is a catalyst comprising rhodium, ruthenium or iridium, comprising a metal complex containing nitrogen-containing polycyclic compound or CO as a ligand, or a metal catalyst comprising an element belonging to Group 11 of the periodic table. Item 3. The method for generating hydrogen according to Item 1 or 2 above.
4). The hydride is of the general formula: X (YH _4-n Z _n ), where X is an alkali metal, NH ₄ , or M _1/2 , where M is an alkaline earth metal; Y is B, Al or Ga, Z is a halogen atom or a monovalent hydrocarbon group, and n is an integer of 0 to 3, and the hydroxide has the general formula: Any of the above items 1 to 3, which is a compound represented by AOH (wherein A is an alkali metal, NH ₄ , or M _1/2 (wherein M is an alkaline earth metal)) The hydrogen generation method according to claim 1.
5). A hydrogen generator comprising an electrolytic cell for causing an electrochemical oxidation reaction of hydride and an electrochemical reduction reaction of protons, and an anode electrode and a cathode electrode inserted in the electrolytic cell,
A hydrogen generator using ruthenium oxide as a catalyst for a cathode electrode.
6). Item 6. The hydrogen generator according to Item 5, wherein the electrolytic cell has a one-chamber structure having no diaphragm for separating the anode and the cathode.

  The hydrogen generation method of the present invention is a method using an anode reaction including an electrochemical oxidation reaction of a hydride and a cathode reaction including a hydrogen generation reaction by reduction of protons in a solution containing a hydride and a hydroxide. .

In this method, 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 ⁻
On the other hand, electrons generated by the anode reaction pass through an external circuit and are supplied to the cathode electrode, and the following cathode reaction including hydrogen generation occurs on the surface of the cathode electrode.

The cathode ^{_{reaction: 8H 2 O + 8e - →}} 4H 2 + 8 OH -
The hydrogen generation method of the present invention is a method characterized by using ruthenium oxide as a cathode electrode catalyst in the hydrogen generation method utilizing the above reaction.

  Hereinafter, the hydrogen generation method of the present invention will be specifically described.

Electrolyte Solution In the hydrogen generation method of the present invention, a solution containing a hydride and a hydroxide is used as a raw material solution, that is, an electrolyte solution.

The hydrides, for example, the general formula: represented by _{X (YH 4-n Z n} ) may be a compound. 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, Cs and the like, examples of the alkaline earth metal include Mg, Ca, Sr, Ba and the like, and examples of the halogen atom include F,
Cl, Br, 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.

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 non-aqueous 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 0.01 to 10 mol / L.

The hydroxide concentration is preferably about 0.0001 to 20 mol / L, and 0.01 to 4 mol / L.
More preferably, it is about.

Cathode electrode The hydrogen generation method of the present invention is characterized in that ruthenium oxide is used as a catalyst for the cathode electrode in the hydrogen generation method utilizing the anode reaction and cathode reaction in the above-described electrolyte. . According to the inventor's research, ruthenium oxide has high activity for electrochemical reduction reaction of protons, and activity for chemical decomposition reaction of hydride and activity for electrochemical oxidation reaction. It became clear that it was a very low substance. Therefore, when ruthenium oxide is used as a cathode electrode catalyst, the cathode reaction can proceed smoothly in the hydrogen generation method using the electrochemical oxidation reaction of the hydride as an anode reaction. The natural decomposition of hydride hardly progresses in the liquid. For this reason, when a solution containing a hydride and a hydroxide is used as the electrolyte, it is not necessary to separate the electrolyte that contributes to the anode reaction and the electrolyte that contributes to the cathode reaction, and the same electrolyte is used. It becomes possible to do.

In the present invention, the ruthenium oxide may be any oxide containing IV valent ruthenium. For example, ruthenium represented by a composition formula: RuO ₂ .xH ₂ O (x is a numerical value of 0 to 4). An oxide can be used. In particular, an oxide having x = 0 in the composition formula is preferable in terms of high electric conductivity.

Especially as this ruthenium oxide, a thing with favorable electroconductivity is suitable, and it is preferable that a resistivity is ^10-2 ohm ^- cm or less, and it is more preferable that it is ^10-3 ohm-cm or less.

  The structure of the cathode electrode using ruthenium oxide as a catalyst is not particularly limited, and a current collector similar to that used in various types of batteries is used as a support, and ruthenium oxide is used in accordance with a conventional method. The supported one can be used as the cathode electrode. As such a support, for example, an aluminum plate, carbon paper, or the like can be used.

  The catalyst made of ruthenium oxide may be supported on a conductive carrier.

  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 oxide is dissolved in a solvent composed of water, an organic solvent, etc., and a conductive carrier is added to this solution, and stirred for several hours, for example, to adsorb the metal oxide on the carrier. After that, the solvent may be dried. In addition, when the solvent contains a large amount of metal oxide, the metal oxide is not adsorbed on the conductive support by filtering after adsorbing the metal oxide on the conductive support until equilibrium is reached. Can be removed, leaving only the metal oxide interacting with the support 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 oxide. 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 water or an organic solvent until the washing liquid becomes transparent, the metal oxide having a weak interaction with the conductive carrier can be washed away, and the conductive carrier is firmly attached. A highly active catalyst containing only the metal oxide adsorbed on the catalyst can be obtained.

  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 catalyst to be supported on the conductive support is not particularly limited, but for example, it is preferable to support about 10 μmol to 150 μmol of metal oxide with respect to 1 g of conductive support, and about 20 μmol to 100 μmol. Is more preferable.

Although there is no particular limitation on the supported amount of ruthenium oxide in the cathode, for example, it is a 0.1 to 5.0 mg / cm ² or so, be 0.1-3.0 mg / cm ² of about Is preferred.

The anode electrode anode catalyst is a substance having an activity for the electrochemical oxidation reaction of the hydride used as a raw material, and the hydride chemistry so that the oxidation reaction of the hydride does not proceed during open circuit. Any catalyst can be used without particular limitation as long as it has a low activity with respect to a general oxidation reaction.

  Specific examples of such a catalyst include a metal complex containing rhodium, ruthenium or iridium as a metal component and a nitrogen-containing polycyclic compound or CO as a ligand. In addition, elements belonging to Group 11 of the periodic table can also be suitably used as an anode electrode catalyst in the hydrogen generator of the present invention in a metal state.

  Hereinafter, these anode electrode catalysts will be described in detail.

(I) Metal complex As a metal component containing rhodium, ruthenium or iridium as a catalyst metal component, examples of the nitrogen-containing polycyclic compound used as a 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. In addition, since the metal complex has low activity for the chemical oxidation reaction of hydride, the electrode to which the metal complex is added hardly progresses the decomposition reaction of hydride when not connected to the cathode electrode. .

  In the present invention, any noble metal complex containing the above-described metal component and containing a nitrogen-containing polycyclic compound or CO as a ligand can be used without any particular limitation. It is not particularly limited.

  Hereinafter, specific examples of the above metal complexes will be shown.

  (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 rhodium, ruthenium or iridium. The metal porphyrin complex represented by this.

  In the above chemical formula, the central metal element represented by M is rhodium, ruthenium or iridium, and rhodium is particularly preferable in that it has a high activity for the electrochemical oxidation reaction of hydride.

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.

    (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 rhodium, ruthenium or iridium, provided that at least one of R _{1 to} R ₈ is a group: —R ₉ A metal porphyrin complex represented by -COOM ₂ ).

  In the above chemical formula, the central metal element represented by M is rhodium, ruthenium or iridium, and rhodium is particularly preferable in that it has a high activity for the electrochemical oxidation reaction of hydride.

  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 , examples of the alkylene group represented by R ₉ include methylene, ethylene, trimethylene, 2-methyltrimethylene, 2,2-dimethyltrimethylene, 1-
Examples thereof include straight-chain or branched alkylene groups having 1 to 6 carbon atoms such as methyltrimethylene, methylmethylene, 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. M represents a rhodium, ruthenium or iridium) metal phthalocyanine complex.

  In the above chemical formula, the central metal element represented by M is rhodium, ruthenium or iridium, and rhodium is particularly preferable in that it has a high activity for the electrochemical oxidation reaction of hydride.

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:

(Wherein, M is rhodium, ruthenium or iridium).

  In the above chemical formula, the central metal element represented by M is rhodium, ruthenium or iridium, and rhodium is particularly preferable in that it has a high activity for the electrochemical oxidation reaction of hydride.

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

  (5) A complex containing one or more molecules of CO as a ligand per metal atom.

In the complex containing CO as a ligand, the number of metal atoms in the complex is preferably about 1 to 10. CO may be coordinated to one metal or may be coordinated to a plurality of metal atoms. When coordinated to a plurality of metal atoms, it is in a state of being crosslinked by CO. There are no particular limitations on the type of ligand other than CO. The metal element in the complex is rhodium, ruthenium or iridium, and rhodium is particularly preferred because it has a high activity for the electrochemical oxidation reaction of hydride.

Examples of such a metal complex containing CO as a ligand include a metal complex represented by the chemical formula: Rh ₂ Cl ₂ (CO) ₄ , a metal complex represented by Rh ₆ (CO) ₁₆ , and the like.

  The above-described metal complexes (1) to (5) can be produced, for example, by dissolving a compound that serves as a ligand of the target complex and the metal compound in a solvent and heating.

  For example, for the rhodium complex, a compound body containing a monovalent rhodium metal can be used as the rhodium compound. As the solvent, a solvent capable of dissolving the above-described ligand compound and rhodium compound may be used. For example, ethanol may be used. The heating temperature may be, for example, the reflux temperature of the solvent used.

Further, for example, a metal complex containing CO represented by the chemical formula: Rh ₂ Cl ₂ (CO) ₄ as a ligand can be easily obtained as a commercial product.

  Among the above metal complexes, in particular, the 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 rhodium). Metal porphyrin complexes are preferred. In particular, R ₁ , R ₄ , R ₇ and R ₁₀ are phenyl groups which may have a substituent, and R _2, R ₃ , R ₅ , R ₆ , R ₈ , R ₉ , R ₁₁ and R ₁₂ Is a hydrogen atom; R ₁ , R ₄ , R ₇ and R ₁₀ are hydrogen atoms, R _2, R ₃ , R ₅ , R ₆ , R ₈ , R ₉ , R ₁₁ and R _An octaalkylporphyrin complex in which ₁₂ is a lower alkyl group is preferred. Among these, preferred specific examples of the tetraphenylporphyrin complex include rhodium tetraphenylporphyrin complex, and preferred specific examples of the octaalkylporphyrin complex include rhodium octaalkylporphyrin.

  The above-described metal complex may be used as an anode catalyst as it is, but can have a high catalytic activity for the electrochemical oxidation reaction of hydride by being supported on a conductive carrier.

  The type of conductive carrier, the loading method, and the like may be the same as those for the cathode catalyst.

  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 150 μmol of the metal complex with respect to 1 g of the conductive carrier, and about 20 μmol to 100 μmol. Is more preferable.

(Ii) Elements belonging to Group 11 of the Periodic Table Elements belonging to Group 11 of the Periodic Table can be effectively used as an anode catalyst in the metal state (hereinafter sometimes referred to as Group 11 metal catalyst). Among group 11 metal catalysts, copper, silver, gold and the like can be exemplified as preferable ones. The form of the Group 11 metal catalyst is not particularly limited, and may be a fine powder metal, or a plate-like or linear metal may be used as an electrode as it is.

(Iii) Structure of anode electrode The structure of the anode electrode is the same as that used for batteries, etc., except for using the above-mentioned metal complex or Group 11 metal catalyst as a catalyst. Any body may be used as long as it supports the above-described anode electrode catalyst.

Although there is no particular limitation on the amount of catalyst supported in the anode electrode, 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 of about .

  In addition, a plate-like or linear 11-group metal catalyst can be used as an anode electrode as it is.

Hydrogen generation method In the hydrogen generation method of the present invention, the above raw material solution (electrolyte) is supplied into an electrolytic cell in which an anode and a cathode are arranged, and the anode and the cathode are electrically connected using an external circuit. What is necessary is just to combine.

  In this method, 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. In this case, as the potential of the anode electrode with respect to the cathode electrode decreases, the amount of hydrogen generated decreases. Therefore, it is usually preferable that the potential of the anode electrode with respect to the cathode electrode be higher than about -0.05V.

  On the other hand, 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 proceed by increasing the potential of the anode electrode using an external power source. 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 this case, the higher the potential of the anode electrode, the more hydrogen is generated, but the power consumption increases. Therefore, it is usually appropriate that the potential of the anode electrode with respect to the cathode electrode is about 0.6 V or less. It is preferably about 0.25V to 0.35V.

  The reaction temperature is not particularly limited, and the reaction can usually proceed at room temperature.

  In the hydrogen generation method of the present invention, the electrolytic cell is not particularly limited as long as the above-described cathode electrode and anode electrode can be disposed simultaneously and can stably contain a solution containing a hydride and a hydroxide used as raw materials. Can be used. For example, an electrolytic cell having an arbitrary shape such as a round shape or a box shape can be used. The material of the electrolytic cell is not particularly limited as long as it can stably accommodate an electrolytic solution made of metal such as stainless steel or resin such as polypropylene.

  In the hydrogen generation method of the present invention, since a solution containing a hydride and a hydroxide is used as both the electrolyte solution on the cathode electrode side and the electrolyte solution on the anode electrode side, no diaphragm is disposed between the cathode electrode and the anode electrode. A one-chamber electrolytic cell can be used. FIG. 1 is a schematic diagram showing a schematic structure of a hydrogen generator using a one-chamber electrolytic cell. The ruthenium oxide used as the cathode electrode catalyst in the hydrogen generation method of the present invention is a substance having a very low activity against the chemical oxidation reaction of the hydride used as a raw material, and is a one-chamber type without the diaphragm shown in FIG. Even in the case of using an electrolytic cell, the hydride self-decomposition reaction hardly occurs at the cathode electrode. For this reason, even in a one-chamber type hydrogen generator with a simple structure, it is possible to control the hydrogen generation rate, hydrogen generation amount, etc. by adjusting the open / close state of the external circuit and the potential of the anode with respect to the cathode It becomes.

  The above-described hydrogen generator can further be provided with a raw material inlet, a generated hydrogen discharge port, and the like as necessary. 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.

  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 may be joined to the hydrogen supply line and the generated hydrogen may be supplied to the fuel cell.

  According to the hydrogen generation method of the present invention, a hydrogen generation reaction is performed using a solution containing a hydride and a hydroxide as a common electrolyte without distinguishing between an electrolyte on the anode side and an electrolyte on the cathode side. Can be controlled with good control.

  In particular, when a catalyst whose anode electrode potential is lower than that of the cathode electrode during the open circuit is used as the anode electrode catalyst, the cathode reaction and the anode reaction are allowed to proceed spontaneously by closing the external circuit. Simultaneously with the generation of hydrogen, the potential difference between the cathode potential and the anode potential can be acquired as electric energy. 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.

  In addition, according to the hydrogen generation method of the present invention, it is possible to use an electrolytic cell consisting of a single chamber without a diaphragm. In this case, the hydrogen generation reaction can be controlled with a simple hydrogen generator. The amount of hydrogen generation, the rate of hydrogen generation, etc. can be easily controlled.

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

Reference Example 1: Proton reducing ability of ruthenium oxide 5 mg of commercially available ruthenium oxide (RuO ₂ ) in 0.5 mL mixed solvent (water: ethanol = 1:
After suspending in 1), 5 μL of 5% Nafion solution (manufactured by Aldrich) was added. This suspension is placed in an ultrasonic cleaner for 5 minutes to disperse well, and then a glassy carbon electrode (surface area =
2 μL on 0.071 cm ² ) and dried.

  With respect to the electrode thus prepared, the hydrogen generation activity in the presence and absence of borohydride ions was measured by the following method using a potentiostat (ALS model 711B) manufactured by ALS.

A glassy carbon electrode coated with ruthenium oxide was used as a working electrode, a platinum electrode as a counter electrode, and an Ag / AgCl / KCl (sat.) Electrode as a reference electrode. As the electrolytic solution, 0.1 M NaOH was used. Cyclic voltammetry was measured under these conditions. Next, NaBH ₄ was added to the above solution to 1 mM, and linear sweep voltammetry was measured while rotating the electrode at a speed of 3600 rpm.

The results are shown in FIG. Curve A is a cyclic voltammogram for an electrolyte containing no NaBH ₄ , and curve B is a linear sweep voltammogram for an electrolyte containing 1 mM NaBH ₄ .

In curves A and B, it can be seen that the reduction current begins to flow from around -1.0 V, and hydrogen is generated due to the reduction of water. NaBH ₄ As is apparent from the curve B measured for electrolyte containing, in the presence of NaBH _4, oxidation current of NaBH ₄ it can be seen that hardly flows. From this result, it became clear that ruthenium oxide is a catalyst having activity against hydrogen generation by electrochemical reaction without causing oxidation reaction of NaBH ₄ .

Examples 1 to 7: Hydrogen generation experiment using a single-chamber hydrogen generator 0.2 ml of the ruthenium oxide suspension prepared in Reference Example 1 was placed on a glassy carbon electrode (effective surface area = 4.5 cm ² ) and dried. Thus, a cathode electrode was produced.

On the other hand, an anode electrode was produced in the same manner as the cathode electrode production method except that each anode electrode catalyst shown in Table 1 below was used. However, for the anodes of Examples 6 and 7, a gold or silver flat plate (effective surface area = 4.5 cm ² ) was used.

A 0.1 M NaOH aqueous solution containing 10 mM NaBH ₄ was put in a glass container sealed with a silicon stopper shown in FIG. After removing dissolved oxygen from the aqueous solution by purging with argon, the cathode and anode prepared by the method described above were immersed in the solution. The gas outlet was closed and allowed to stand for 100 minutes to quantify hydrogen gas in the gas phase.

Next, after the electrolytic solution was purged with nitrogen again, a voltage was applied between both electrodes so that the potential of the anode with respect to the cathode was 0.3 V, and then the hydrogen gas in the gas phase was quantified. The determination of hydrogen gas in the gas phase was performed after 33 minutes for Example 1, 83 minutes for Example 2, 100 minutes for Example 3, and 85 minutes for Example 4. 5 was done 67 minutes later. Also,
For Example 6, a voltage was applied between both electrodes so that the potential of the anode electrode with respect to the cathode electrode was 0.5 V, and then the amount of hydrogen gas was quantified 100 minutes later. A voltage was applied between the electrodes so that the electrode potential was 0.6 V, and the amount of hydrogen gas was determined 67 minutes later.

Table 1 below shows the amount of hydrogen generated per unit time and the increase ratio by applying voltage (open circuit without applying voltage / voltage applied when voltage is applied). The amount of hydrogen in the state) and the number of moles of electrons transferred. A hydrogen generating device having a high increase ratio (amount of hydrogen after electrolysis / amount of hydrogen in an open circuit state where no voltage is applied) and a high amount of hydrogen after electrolysis is considered to be a better hydrogen generator.

  From the above, even when any of the anode electrode catalysts of Examples 1 to 7 is used, in the open circuit state where no voltage is applied, the amount of hydrogen gas generated is small, but when a voltage is applied, current flows and hydrogen gas is generated. It became clear that the generation amount can be greatly increased. Therefore, this apparatus can be said to be a controllable hydrogen generating apparatus that can advance the hydrogen generating reaction with a small voltage.

Example 8
Commercially available ruthenium oxide (RuO ₂ ) (5.2 mg) in 0.5 mL mixed solvent (water: ethanol = 1
: After suspension in 1), 5 μL of 5% Nafion solution (manufactured by Aldrich) was added. 5 of this suspension
The glassy carbon electrode (surface area)
= 0.071 cm ² ) 2 μL on the cathode and dried.

On the other hand, as an anode electrode catalyst, each of the metal complexes of Example 1 (rhodium octaethylporphyrin) and Example 4 (rhodium hematoporphyrin) was used to prepare an anode electrode in the same manner as the above cathode electrode preparation method. .

A 0.1 M NaOH aqueous solution containing 10 mM NaBH ₄ was put in a glass container sealed with a silicon stopper shown in FIG. After removing the dissolved oxygen from the aqueous solution by purging with nitrogen, the cathode electrode and the anode electrode were immersed. In order to eliminate the influence of the charge capacity of RuO ₂ , a current of 0.1 μA was first flowed to charge all the charge capacity to stabilize the voltage, and then the potential-current curve was measured. As for the potential, a value one minute after changing the current was recorded. The results are shown in FIG.

  As is apparent from FIG. 3, it can be seen that in this potential region, hydrogen generation occurs while generating power.

It is a schematic block diagram which shows one Embodiment of the one-chamber type hydrogen generator of this invention. 2 is a voltammogram measured in Reference Example 1. 10 is a graph showing a potential-current curve measured in Example 8.

Claims (6)

A method for generating hydrogen by causing an anode reaction including an electrochemical oxidation reaction of a hydride and a cathode reaction including a hydrogen generation reaction by reduction of protons in an electrolyte solution containing a hydride and a hydroxide, A method comprising using ruthenium oxide as a cathode electrode catalyst. The method for generating hydrogen according to claim 1, wherein the ruthenium oxide is a compound represented by a composition formula: RuO ₂ .xH ₂ O (x is a numerical value of 0 to 4). The anode catalyst is a catalyst comprising rhodium, ruthenium or iridium, comprising a metal complex containing nitrogen-containing polycyclic compound or CO as a ligand, or a metal catalyst comprising an element belonging to Group 11 of the periodic table. The method for generating hydrogen according to claim 1 or 2. The hydride is of the general formula: X (YH _4-n Z _n ), where X is an alkali metal, NH ₄ , or M _1/2 , where M is an alkaline earth metal; Y is B, Al or Ga, Z is a halogen atom or a monovalent hydrocarbon group, and n is an integer of 0 to 3, and the hydroxide has the general formula: Any one of claims 1 to 3, which is a compound represented by AOH (wherein A is an alkali metal, NH ₄ , or M _1/2 (wherein M is an alkaline earth metal)). The hydrogen generation method according to claim 1. A hydrogen generator comprising an electrolytic cell for causing an electrochemical oxidation reaction of a hydride and an electrochemical reduction reaction of a proton, and an anode electrode and a cathode electrode inserted into the electrolytic cell, the catalyst for a cathode electrode A hydrogen generator characterized by using ruthenium oxide. The hydrogen generator according to claim 5, wherein the electrolytic cell has a one-chamber structure having no diaphragm for separating the anode and the cathode.

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