JPH08269762A - Catalytic electrode for oxidation of water and its production - Google Patents

Abstract

PURPOSE: To attain the oxidation of water at low oxidation potential by using a specified metallic component, a specified metallic complex component and a specified carrying method when a metallic component and a metallic complex component are carried on the surface of a substrate to obtain a catalytic electrode for oxidation of water. CONSTITUTION: A metallic component used for an electrode is one or more kinds of elements and/or oxides selected from among group VIII elements of the Periodic Table and their oxides and a metallic complex component is a water oxidation catalyst. The components are carried as a mixture or in a separate state on a carrier made of a polymer film, clay or an interlaminar compd. and formed in a layer shape on at least a part of an electrode substrate. The metallic component is preferably one selected from among Ru, Pt and Ir, the metallic complex component consists preferably of Ru or Mn and an N-contg. ligand and the weight ratio between the metallic component and the metallic complex component is (10-10<5> ):1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode used for decomposing water, and more particularly to a catalyst for oxidizing water which can oxidize water at a low oxidation potential and a method for producing the same.

[0002]

2. Description of the Related Art
As an electrode for oxidation of water used in electrolysis of water, etc.
Noble metals such as platinum and metal oxides (RuO ₂ , IrO ₂ , P
bO ₂ , ferrite, etc.), graphite, etc. have been used (Chemical Handbook, Applied Chemistry I, p. 200, Maruzen (1986)). Various efforts have been made to increase the efficiency of water decomposition. As one of them, it is conceivable to use a water oxidation catalyst such as a metal complex. However, the present inventors have confirmed that even if an oxidation catalyst is directly provided on the electrode, the transfer of electrons to the electrode is hindered, and the water decomposition efficiency is reduced.

On the other hand, in the case of artificial photosynthesis, if a water oxidation catalyst is provided on a water oxidation electrode composed of a photocatalytic semiconductor, not only does light irradiation be prevented, but the improvement of water decomposition efficiency cannot be obtained for the above-mentioned reasons. In order to improve the efficiency of water decomposition, holes supplied from the photoexcitation system are efficiently transferred to the oxidation electrode without hindering light irradiation, and then water is oxidized on the electrode surface under conditions where the overvoltage is as low as possible. There is a need to

That is, there is a demand for an electrode having water oxidation characteristics and capable of efficiently receiving electrons, that is, an oxidation electrode having a low water oxidation potential.

Accordingly, an object of the present invention is to provide a water oxidation catalyst electrode capable of oxidizing water at a low oxidation potential and a method for producing the same.

[0006]

Means for Solving the Problems As a result of intensive studies in view of the above problems, the present inventors have found that a metal and / or metal oxide and a metal complex which is an oxidation catalyst for water are supported on an electrode substrate. It was discovered that an oxidation electrode having a low oxidation potential was obtained, and the present invention was completed.

That is, the catalyst electrode for oxidizing water of the present invention has a metal component and a metal complex component supported on the surface of an electrode substrate, and the metal component is an element belonging to Group 8 of the periodic table and a metal component thereof. And / or an oxide selected from the group consisting of oxides of the above, wherein the metal complex component is a catalyst for oxidizing water.

[0008] In addition, the surface of the electrode substrate has an eighth element of the periodic table.
For oxidizing water, comprising a metal component comprising at least one element and / or compound selected from the group consisting of group III elements and their oxides, and a metal complex component which is a catalyst for oxidizing water. A first method of the present invention for producing an electrode is characterized in that a thin film is formed on the electrode substrate after mixing the metal component and the metal complex component.

Further, a metal component comprising at least one element and / or compound selected from the group consisting of elements of Group VIII of the periodic table and their oxides on the surface of the electrode substrate;
A second method of the present invention for producing a water oxidation catalyst electrode comprising a metal complex component that is a catalyst for oxidizing water,
After forming the metal component in a thin film on the electrode substrate,
The method is characterized in that the metal complex component is formed in a thin film on the metal component layer.

Hereinafter, the present invention will be described in detail. [1] Water Oxidation Electrode The water oxidation electrode of the present invention comprises a metal component and a metal complex component supported on an electrode substrate.

(A) Electrode substrate When used for electrolysis of water, the electrode substrate is made of a noble metal such as platinum or a metal oxide (RuO ₂ , IrO ₂ , PbO ₂ , ferrite, etc.), graphite, graphite or the like.

In the case of an oxidation electrode for artificial photosynthesis water, the electrode substrate is made of a semiconductor which is a photocatalyst. Specifically, n
An electrode substrate made of -Cds, n-CdSe, N-GaP, or the like.

(B) Metal component The metal component is one or more elements and / or oxides selected from the group consisting of Group 8 elements of the periodic table and their oxides, preferably Ru, Pt, Ir is at least one element and / or oxide, particularly preferably Ru element and / or oxide thereof. Two or more metals and / or oxides thereof may be used together.
By supporting the metal component on the electrode substrate, electrons can be efficiently transferred between the water oxidation catalyst and the electrode.

The loading amount of the metal component with respect to the loading area of the electrode surface is preferably 0.1 to 20 mg / cm ² , and 0.5 to ²⁰ mg / cm ^2.
10 mg / cm ² is more preferred. If the supported amount of the metal component is less than 0.1 mg / cm ² , the electron transfer efficiency is not improved, and if the supported amount of the metal component exceeds 20 mg / cm ² , the stability is lowered, which is not preferable.

(C) Metal complex component The metal complex component is a compound capable of oxidizing water by itself. Specific examples include a complex composed of ruthenium, manganese, or the like and a nitrogen-containing ligand. Examples of the nitrogen-containing ligand include 2,2′-bipyridine, ammine, o-phenanthroline and the like. For example, an ammine ligand type Ru trinuclear complex (formula 1), a pentaammine Ru complex (formula 2), a tetrakis (2,2′-bipyridine) -μ-oxo-ziruthenium complex (formula 3), a tetrakis ( 2,2 '
-Bipyridine) -di-oxo-dimanganese complex (formula 4).

[0016]

(Equation 1)

[0017]

(Equation 2)

[0018]

(Equation 3)

[0019]

Formula 4 (where X ⁻ represents an anion)

The loading amount of the metal complex component with respect to the loading area of the electrode surface is preferably 0.001 to 1 mg / cm ² ,
0.01 to 0.1 mg / cm ² is particularly preferred. If the supported amount of the metal complex component is less than 0.001 mg / cm ² , the oxidation efficiency of water is not improved, and if the supported amount of the metal complex component exceeds 1 mg / cm ² , the complex is deactivated by self-decomposition. Undesirably occurs. In the case of an artificial photosynthesis electrode, the amount of the metal complex component to be carried is particularly preferably 0.01 to 0.1 mg / cm ² so as not to hinder the irradiation of light to the electrode substrate.

The weight ratio between the metal component and the metal complex component is 1
It is preferably 0: 1 to 10 ⁵ : 1 and 10: 1 to 1
It is particularly preferred that the ratio be 0 ⁴ : 1. If the weight ratio of the metal component to the metal complex component is less than 10: 1, the activity is rather reduced. If the weight ratio exceeds 10 ⁵ : 1, the activity is still not sufficiently imparted.

(D) Form of Water Oxidation Electrode Within the above range, the water oxidation electrode of the present invention can take various forms. Hereinafter, embodiments of the present invention will be described with reference to examples, but these examples do not limit the present invention.

(I) A mixture of an electrode metal component and a metal complex component is formed in a layer on at least a part of the surface of an electrode substrate.

The mixture can be directly carried on the electrode substrate, but the mixture can be carried on a carrier and then carried on the electrode substrate. Examples of the carrier include a polymer film, an interlayer compound, and clay. Specifically, a perfluoroalkylsulfonic acid polymer (hereinafter, referred to as Nafion) and polystyrenesulfonic acid are used as the polymer film, and zeolite and tetratitanic acid are used as the interlayer compound.

(Ii) The metal component is formed in a layer on at least a part of the surface of the electrode substrate, and the metal complex component is formed in a layer on at least a part of the surface of the metal component layer. The metal complex component layer may be formed directly on the metal component layer, or the metal complex component may be supported on the above-described carrier and then formed on the metal component layer. The total layer thickness of the metal component layer and the metal complex component layer is preferably 100 μm or less, particularly preferably 10 μm or less.

When the metal component is formed in a layer and a metal complex component layer is formed thereon, it is preferable that the metal complex component layer has a thickness of 10 ³ or less, that is, a layer having a height of 10 ³ molecules or less. It is preferable to use a layer, that is, a layer having a height of one molecule.

[2] Method for Producing Water Oxidation Electrode The method for producing the water oxidation electrode of the present invention differs depending on the above-described embodiment. In the first method of the present invention, a thin film is formed on an electrode substrate after mixing a metal component and a metal complex component. As a method for forming a thin film on the electrode substrate, a casting method or an immersion method can be used.

The metal component and the metal complex component can be mixed by a known method. The metal component powder and the metal complex component powder can be mixed by a known method. By carrying the components individually or simultaneously, the metal component and the metal complex component can be used by being dispersed or adsorbed in a solid phase matrix such as a polymer film. In this case, the carrier supporting the metal component and the metal complex component is formed into a thin film on the electrode substrate by using a method such as a casting method, spin coating, and vapor deposition method.

According to a second method of the present invention, after the metal component is formed on the electrode substrate in a thin film, the metal complex component is formed on the metal component layer in a thin film.

(A) Method of Carrying Metal Component The metal component can be formed into a thin film of a desired thickness on the electrode substrate by a method such as a vacuum evaporation method, a high-frequency sputtering method, and an ion plating method. Alternatively, the electrode substrate may be immersed in an aqueous solution of a metal component salt, and a reduction potential may be applied to reduce the ions of the metal component and deposit the metal on the electrode to form a thin film. After the metal component thin film is formed, the electrode is subjected to a heat treatment in the presence of oxygen, whereby a metal oxide thin film can be obtained.

(B) Method of Carrying Metal Complex Component A thin film layer of the metal complex component can be formed on the metal component layer by using a casting method or an immersion method. A thin film layer can be formed on the component layer. For example, after the metal complex solution is added onto the metal component layer, the solvent is removed and dried, so that the surface of the metal component layer is coated with the metal complex component.
Alternatively, the electrode substrate on which the metal component layer is formed is immersed in the metal complex solution and then the solvent is removed, thereby forming a thin film layer of the metal complex component on the surface.

[0032]

As described above, the water oxidation catalyst electrode of the present invention fuses the water oxidation catalyst and the electrode by supporting a metal component and a metal complex component on the electrode substrate, and thus has an electron accepting efficiency. And thereby promote the oxidation of water.

[0033]

The present invention will be described in more detail with reference to the following specific examples. Example 1 Basal Plan in which carbon six-membered ring planes are arranged in parallel with the electrode surface
e Pyrolytic Graphite electrode (hereinafter abbreviated as BPG electrode, surface area: 0.17 cm ² ) 0.2 m with working electrode and platinum plate as counter electrode
Immersed in 10 mM chloroplatinic acid aqueous solution containing M lead acetate,
A voltage of 2.0 V was applied between the BPG electrode and the counter electrode to deposit platinum fine particles on the BPG electrode. Thereafter, the same operation was performed in a 1 M aqueous sulfuric acid solution to prepare a BPG electrode modified with platinum fine particles (platinum black). The amount of the deposited platinum fine particles is about 1.
2 mg.

By adding 10 μl of a 0.6 mM aqueous solution of the metal complex ammine ligand type Ru trinuclear complex to the platinum fine particles and drying, about 3.2 μg of the ammine ligand type Ru trinuclear complex is formed on the platinum fine particles. Was adsorbed. Pt at this time
The weight ratio of the trinuclear complex / ammine ligand type is about 370: 1.
It is. Using this Pt / ammine ligand type Ru trinuclear complex-modified electrode as a working electrode, a triode cell was placed in a 0.1 M sodium perchlorate aqueous solution, the counter electrode was a platinum plate, and the reference electrode was Ag / AgCl. Then, argon gas was blown into the solution to replace the air with argon, followed by sealing. When an oxidation potential was applied, water was oxidized, and oxygen bubbles were generated on the catalyst.

After performing the electrolysis at a constant potential for 1 hour, the gas was sampled with a syringe, and the generated oxygen was qualitatively and quantitatively determined by gas chromatography equipped with a column of Molechara sheep 5A. The oxidation potential with respect to the reference electrode was changed in the range of 1.05 to 1.4 V, and the amount of oxygen generated at each potential was measured. FIG. 1 shows the relationship between the amount of generated oxygen and the applied oxidation potential. Table 1 shows the amount of oxygen generated when the applied oxidation potential was 1.2 V.

Comparative Example 1 1.2 mg of platinum fine particles (platinum black) in the same manner as in Example 1.
A BPG electrode modified with was prepared. This platinum black modified BP
Using the G electrode, water electrolysis was performed in the same manner as in Example 1, and the amount of generated oxygen was measured. FIG. 1 shows the relationship between the amount of generated oxygen and the applied oxidation potential. Table 1 shows the amount of oxygen generated when the applied oxidation potential was 1.2 V.

Comparative Example 2 Using the same unmodified BPG electrode as in Example 1, water was electrolyzed in the same manner as in Example 1, and the amount of generated oxygen was measured. The results are shown in FIG.

As can be seen from FIG. 1, at any oxidation potential, the electrode modified with Pt and the trinuclear complex of ammine ligand type Ru (Example 1) was better than the electrode modified with Pt alone (Comparative Example 1). Show much higher oxygen evolution, Pt
It can be seen that the coexistence of a triamine complex with an ammine ligand type Ru acts as a highly active oxidation catalyst. The potential at which oxygen starts to be generated is 1.0 in the Pt / ammine ligand type Ru trinuclear complex-modified electrode (Example 1) system.
5 V (vs. the reference electrode), which was 0.1 V higher than 1.15 V of the modified electrode only for Pt of Comparative Example 1, and the overpotential of oxygen generation was smoother for the supported electrode of Pt and the ammine ligand type Ru trinuclear complex. Indicates small.

Example 2 An electrocatalytic water oxidation reaction was carried out in the same manner as in Example 1 except that a platinum plate electrode having a surface area of 1 cm ² was used in place of the BGP electrode. An electrode coated with black was prepared, and 3 μm was formed in the same manner as in Example 1.
g of ammine ligand type Ru trinuclear complex was supported. Water was electrolyzed at an oxidation potential of 1.2 V in the same manner as in Example 1, and the amount of generated oxygen was measured.

Comparative Examples 3 and 4 The same method as in Example 1 was used, using the same unmodified platinum plate electrode (Comparative Example 3) and platinum black-modified platinum plate electrode (Comparative Example 4) as in Example 2. Was subjected to electrolysis of water at an oxidation potential of 1.2 V, and the amount of generated oxygen was measured.

Example 3 A Pt (1.2 mg) / pentaammine Ru complex (1.5 mg) was prepared in the same manner as in Example 1 except that a pentaammine Ru complex was used as the metal complex instead of the ammine ligand type Ru trinuclear complex. μg) A modified BPG electrode was prepared. The procedure was the same as in Example 1. Water was electrolyzed at an oxidation potential of 1.2 V, and the amount of generated oxygen was measured.

Example 4 Using the same BPG electrode as in Example 1, a platinum thin film was formed on the BPG electrode by high frequency sputtering. The amount of platinum supported on the electrode is 0.5 mg. This platinum-modified BPG
Apply 2.5% by weight alcohol solution of Nafion on the electrode
After adding and spreading, the mixture was air-dried, and then immersed in a 1 mM aqueous solution of an ammine ligand-type Ru trinuclear complex to saturate and adsorb 1.5 μg of an ammine ligand-type Ru trinuclear complex. Using this modified electrode, in the same manner as in Example 1, water was electrolyzed at an oxidation potential of 1.2 V, and the amount of generated oxygen was measured.
It was shown to.

COMPARATIVE EXAMPLE 5 Using the platinum-modified BPG electrode prepared in Example 4, water was electrolyzed at an oxidation potential of 1.2 V in the same manner as in Example 1, and the amount of generated oxygen was measured. 1 is shown.

Example 5 5.03 was placed on the same platinum plate electrode (surface area: 1 cm ² ) as in Example 2.
A 1 mM RuO ₂ aqueous solution was immersed, and a reduction potential was applied to deposit 1 mg of RuO ₄ on a platinum plate electrode under the condition of a current density of 1 A / dm ² . On this RuO ₂ -modified platinum plate electrode, a 2.5% by weight alcohol solution of Nafion was cast and dried to form a Nafion film of about 10 μm. This was immersed in an aqueous solution of a 1 mM ammine ligand type Ru trinuclear complex to allow saturated adsorption of a 0.2 M ammine ligand type Ru trinuclear complex in a Nafion membrane, and a RuO ₂ / ammine ligand type trinuclear complex was obtained. An electrode modified with a Ru trinuclear complex was prepared. Using this modified electrode as a working electrode, 1.2 V
The electrolysis of water was performed at the oxidation potential of, and the amount of generated oxygen was measured.

Table 1 Example No. Oxygen generation amount (μl / hr) Example 1 35.1 Example 2 15.7 Example 3 12.5 Example 4 40.3 Example 5 70.1 Comparative Example 15 .52 Comparative Example 2 0 Comparative Example 3 0 Comparative Example 4 2.15 Comparative Example 5 10.2

As can be seen from Table 1, the metal component and the metal complex component were carried in comparison with Comparative Examples 2 and 3 using only the electrode substrate and Comparative Examples 1, 3 and 4 in which the electrode substrate was modified with platinum. The electrode of the present invention generated high oxygen and showed excellent hydroxylation performance.

[0047]

As described above in detail, the catalyst electrode for oxidizing water of the present invention easily accepts electrons from water by supporting a metal component and a metal complex component on the electrode substrate, and quickly converts the water. It can transport electrons. Therefore, water can be oxidized at a low oxidation potential, and the oxidation rate of water can be increased.

The catalyst electrode for oxidizing water of the present invention can be used as an electrode for electrolysis of water, artificial photosynthesis and the like.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of generated oxygen and the applied oxidation potential in Example 1 and Comparative Examples 1 and 2.

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 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Yamashita 4-14-1, Suehiro, Kumagaya-shi, Saitama Pref.Rikken Kumagaya Office (72) Inventor Kiyohide Yoshida 4-14, Suehiro, Kumagaya-shi, Saitama No. 1 Inside the Riken Kumagaya Office

Claims (14)

[Claims] 1. A catalyst electrode for oxidizing water comprising a metal component and a metal complex component supported on a surface of an electrode substrate, wherein the metal component is an element belonging to Group 8 of the periodic table and its oxidation. A catalyst for oxidizing water, wherein the metal complex component is at least one element and / or oxide selected from the group consisting of: 2. The water oxidation catalyst electrode according to claim 1, wherein a mixture of the metal component and the metal complex component is formed in a layer on at least a part of the surface of the electrode substrate. Characteristic catalyst electrode for water oxidation. 3. The catalyst electrode for oxidizing water according to claim 2, wherein the mixture of the metal component and the metal complex component is supported on a carrier comprising a polymer film, clay, or an intercalation compound. A catalyst electrode for oxidizing water, wherein the carrier is formed in a layer on at least a part of the surface of the electrode substrate. 4. The water oxidation catalyst electrode according to claim 1, wherein the metal component is formed in a layer on at least a part of the surface of the electrode substrate, and the metal complex component is a layer of the metal component. A water oxidation catalyst electrode, which is formed in a layer on at least a part of the surface of the catalyst. 5. The catalyst electrode for oxidizing water according to claim 4, wherein the metal complex component is supported on a carrier made of any of a polymer film, clay, and an intercalation compound, and the carrier is formed of the metal component. A water oxidation catalyst electrode, which is formed in a layer on at least a part of the surface of the layer. 6. The catalyst electrode for oxidizing water according to claim 1, wherein the metal component is one or more elements and / or oxides selected from the group consisting of Ru, Pt, and Ir. A catalyst electrode for oxidizing water. 7. The water oxidation catalyst electrode according to claim 1, wherein the metal complex component comprises at least one of ruthenium and manganese and a nitrogen-containing ligand. Oxidation catalyst electrode. 8. The water oxidation catalyst electrode according to claim 7, wherein the metal complex component is an ammine ligand type Ru trinuclear complex (formula 1), a pentaammine Ru complex (formula 2), and tetrakis (2). , 2′-bipyridine) -μ-oxo-diruthenium complex (formula 3) and tetrakis (2,2′-bipyridine) -diμ-oxo-dimanganese complex (formula 4). Catalytic electrode for water oxidation. 9. The catalyst electrode for oxidizing water according to claim 1, wherein a weight ratio of the metal component to the metal complex is 10: 1 to 10 ⁵ : 1. Catalytic electrode for oxidizing water. 10. The catalyst electrode for oxidizing water according to claim 1, wherein the supported amount of the metal component is 0.1 to 20 mg / cm ^{2 with} respect to the supported area of the electrode substrate.
And the loading amount of the metal complex is 0.001 to 1 mg /
oxidation catalyst electrode water which is a cm ^2. 11. A catalyst for oxidizing water and a metal component comprising at least one element and / or compound selected from the group consisting of Group 8 elements of the periodic table and their oxides on the surface of the electrode substrate. A method for producing a catalyst electrode for oxidizing water comprising a metal complex component, wherein the metal component and the metal complex component are mixed and then formed into a thin film on the electrode substrate. A method characterized by the following. 12. The method according to claim 11, wherein after mixing the metal component and the metal complex component, the metal component and the metal complex component are dispersed or adsorbed on a carrier made of a polymer film, clay, or an intercalation compound and supported. Forming a thin film of the carrier on the electrode substrate. 13. A catalyst for oxidizing water and a metal component comprising at least one element and / or compound selected from the group consisting of Group 8 elements and their oxides on the surface of an electrode substrate. A method for producing a catalyst electrode for oxidation of water carrying a metal complex component, wherein the metal component is formed in a thin film on the electrode substrate, and then the metal complex component is coated with the metal component layer. A method comprising forming a thin film thereon. 14. The method according to claim 13, wherein the metal complex component is supported by being dispersed or adsorbed on a carrier made of a polymer film, clay or an intercalation compound, and the carrier is provided on the metal component layer. A thin film.