JP2777677B2 - Method for producing iridium oxide film / metal bonded body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an iridium oxide film / metal assembly mainly intended for use as an anode electrode catalyst, and more particularly, to electrolyze a desired aqueous solution to generate oxygen at the anode. The present invention relates to a method for producing an electrode for oxygen generation used in a reaction and having a low oxygen overvoltage.

[0002]

2. Description of the Related Art Generally, when zinc or tin is electroplated on the surface of steel or the like, a sulfuric acid aqueous solution is used as an electrolytic solution, and a cathode made of a metal base such as steel to be plated, titanium, lead, or the like. The plating is performed by applying a current to the anode electrode. In this case, in order to perform plating with high energy efficiency, it is preferable to lower the voltage applied between the anode and the cathode.

[0003] However, oxygen is generated from the anode at the same time as zinc or tin is plated on the cathode, which causes an oxygen generation overpotential.

[0004] Therefore, a method of coating the surface of the cathode made of the above-mentioned metal base material with a noble metal such as platinum or iridium has been conventionally used in order to reduce the oxygen generation overvoltage. As a method disclosed in JP-A-63-235493, there is a method in which a mixed oxide of iridium oxide and tantalum oxide is coated on the surface of a metal substrate such as titanium by a wet process.

However, this method is disadvantageous in cost because a relatively large amount of metal iridium is required to form a coating.

On the other hand, it has been revealed by Beni et al. That an iridium oxide film exhibits excellent properties as an anode electrode catalyst (Nature, Vol. 282, 281-28).
3 pages, issued November 15, 1979). According to this, iridium oxide has superior properties over iridium as an anode electrode catalyst, and furthermore, the iridium oxide film produced by the reactive sputtering method has a better anode than the iridium oxide film produced by the anodic oxidation method. It is shown to have properties as an electrocatalyst. However, in this method, it is necessary to use plate-like iridium having the same area as the base material as the target material, which is disadvantageous in cost.

Also, a composite film made of metal iridium and carbon is coated on a metal substrate whose surface has been cleaned by a known cleaning method by a method disclosed in Japanese Patent Publication No. 62-57707.
There is known a method for producing an iridium oxide film by heating and oxidizing at about ° C. However, there arises a problem that an iridium oxide film produced by washing a titanium or the like by a known washing method and producing the iridium oxide film in accordance with the above-described method immediately peels off when an electric current is applied in an acidic aqueous solution such as sulfuric acid.

As described above, in the prior art, an iridium oxide / metal junction which is cost-effective and electrochemically stable has not yet been obtained.

[0009]

Means for Solving the Problems The present inventor has conducted intensive studies in view of the above prior art, and as a result, prior to forming an iridium oxide film, the metal substrate was subjected to electrolytic treatment under specific conditions. It has been found that a joined body having excellent anode electrode catalytic properties can be obtained.

That is, the present invention provides the following method for producing an iridium oxide / metal junction. 1. In the method for producing an iridium oxide film / metal assembly, in which a composite film made of metal iridium and carbon is formed on a metal substrate and then heated and oxidized to make the composite film an iridium oxide film, A method for producing an iridium oxide film / metal assembly, wherein a surface electrolytic treatment of the metal substrate is performed by applying an AC voltage in an aqueous sulfuric acid solution. 2. 2. The method for producing an iridium oxide film / metal assembly according to claim 1, wherein the metal substrate is titanium.

Hereinafter, the present invention will be described in detail.

Examples of the metal substrate that can be used in the present invention include titanium, platinum, tantalum, etc. Among them, titanium is particularly preferable.

First, in the electrolytic treatment method, a metal substrate is immersed in a sulfuric acid aqueous solution, and an AC voltage is applied. As the AC voltage, using a saturated sweet potato electrode as a reference electrode, for example, an AC potential of a triangular wave having a period of 30 seconds with a lower limit of -0.25 V and an upper limit of 1.25 V is applied for 1 minute to several hours, preferably for 30 to 60 minutes. .
In addition, processing conditions are not limited to this, -0.5 to
An AC voltage such as a rectangular wave or a sine wave having 0 V as a lower limit potential range and 1 to 1.5 V as an upper limit potential range may be applied.

The concentration of the aqueous sulfuric acid solution is about 0.05 to 4 mol / l, preferably about 0.5 to 1 mol / l.

After the electrolytic treatment, an iridium-carbon composite film is formed. This can be performed by a generally employed evaporation method under vacuum, for example, an electron beam evaporation method or a sputtering method. More specifically, (i) iridium and carbon are evaporated using electron beams from separate evaporation sources to form a composite film on the same substrate, and (ii) iridium is placed in a graphite crucible. To accommodate
A method in which carbon is evaporated together with iridium using an electron beam to form a composite film on a substrate, and (iii) a composite film is formed by sputtering in argon gas using a target having iridium disposed on carbon as a target. And the like. However, it goes without saying that the iridium-carbon composite film can be formed not only by these exemplified methods but also by other methods.

By controlling the evaporation source, an iridium-carbon composite film having an arbitrary composition ratio can be obtained. However, when thermal oxidation is performed, when the composition ratio of iridium to carbon in the composite film is in the range of 0.05 to 0.30. In addition, the formation of an oxide film is improved. That is, when the composition ratio of iridium to carbon in the composite film is less than 0.05 or more than 0.30, desorption of carbon from the iridium-carbon composite film becomes insufficient during thermal oxidation.

Next, the desired iridium oxide film is obtained by heating and oxidizing the iridium-carbon composite film formed on the substrate in the air at about 225 to 350 ° C. for about 10 to 20 minutes. The heating oxidizing atmosphere is not particularly limited as long as the iridium oxide film is formed, and may be, for example, an oxygen-enriched atmosphere or an oxygen- and steam-enriched atmosphere.

[0018]

The iridium oxide film / metal assembly according to the method of the present invention can exhibit excellent electrochemical stability, can reduce oxygen overvoltage during plating or the like, and is very effective in terms of energy efficiency. .

Further, since only a small amount of metal iridium is required for production, it is very advantageous in terms of cost.

[0020]

The following examples are provided to further clarify the features of the present invention.

[0021]

[Example 1] Titanium base material (dimensions: 1 cm x 3-4 cm x 1 mm)
Is immersed in a 0.5 mol / l sulfuric acid aqueous solution, a triangular wave with a period of 30 seconds is applied within a range of -0.25 to 1.25 V using a saturated sweet potato electrode as a standard electrode, and a potential scan is performed for one hour to make a surface. Cleaned.

Thereafter, according to the method described in JP-B-62-57707, that is, iridium powder is put into a graphite crucible, and electron beam evaporation is performed under the conditions of an acceleration voltage of 6 kV and an emission current of 180 to 200 mA, thereby obtaining titanium. An iridium-carbon composite film was formed on a substrate, and then the composite film was heated in the air at 250 ° C. for 10 minutes to form a heated iridium oxide film. The amount of iridium in the iridium oxide film was about 90 μg / cm ^{2 as} a result of X-ray fluorescence analysis.

0.5 mol of the iridium oxide film / titanium assembly (electrode size: 1 cm × 1.4 cm) obtained as described above
/ l of sulfuric acid aqueous solution, and the anode electrode characteristics were examined at a potential of 1.5 V using a saturated sweet pepper electrode as a reference electrode. The time change of the current density at this time is shown by a solid line in FIG.

From this, generation of oxygen was recognized at a current density of 50 mA / cm ² .

[0025]

Comparative Example 1 A mixed oxide / titanium composite of iridium oxide and tantalum oxide formed by a wet process described in JP-A-63-235493 (electrode size: 1 cm ×
(0.7 cm) was immersed in a 0.5 mol / l sulfuric acid aqueous solution, and the anode electrode characteristics were examined at a potential of 1.5 V using a saturated sweet pepper electrode as a reference electrode. The time change of the current density at this time is shown by a broken line in FIG. From this, generation of oxygen was recognized at a current density of 40 to 53 mA / cm ² . As a result of X-ray fluorescence analysis, the amount of iridium in the mixed oxide of iridium oxide and tantalum oxide was about 3 mg / cm ² .

As a result, the iridium oxide film / titanium joined body obtained by the present invention has an extremely small iridium loading amount and is comparable to a mixed oxide / titanium joined body of iridium oxide and tantalum oxide formed by a wet process. It can be seen that the effect is exhibited.

[0027]

Comparative Example 2 A method combining known substrate cleaning methods,
That is, the glass substrate with the tin oxide transparent electrode was cleaned by a cleaning method combining a method using a neutral detergent, a method using a chemical / solvent, and an ultrasonic cleaning method.

Subsequently, the iridium powder was placed in a graphite crucible according to the method described in Japanese Patent Publication No. 62-57707, and electron beam evaporation was performed under the conditions of an acceleration voltage of 6 kV and an emission current of 180 to 200 mA. An iridium-carbon composite film was formed on a titanium substrate, and then the composite film was heated in the air at 250 ° C. for 10 minutes to form a heated iridium oxide film. The amount of iridium in the iridium oxide film was about 50 μg / cm ^{2 as} a result of X-ray fluorescence analysis. Next, a glass substrate assembly having an iridium oxide film / tin oxide transparent electrode (electrode dimensions: 1.1 cm × 2.0 cm) was added at 0.5 mol / l.
The electrode was immersed in a sulfuric acid aqueous solution, and the characteristics of the anode electrode were examined at a potential of 1.5 V with the saturated sweet pepper electrode as a reference electrode.
About 16 mA / cm ² after 1 minute, about 13 mA after 1 hour
Oxygen evolution at a current density of / cm ² was observed. To compare with the anode catalytic properties of iridium oxide film produced by reactive sputtering by Benira reported more apparent, the result of performing a long energization experiment, about 10 mA / cm ² after 20 hours Oxygen evolution was observed at a current density of. The potential of 1.5 V using the saturated sweetfish electrode as a reference electrode is
Corresponding to about 1.75 V with the hydrogen electrode as the reference electrode, the iridium oxide film produced by the reactive sputtering method reported by Beni et al. Was 1.75 V with the hydrogen electrode in a 0.5 mol / l sulfuric acid aqueous solution as the reference electrode. Oxygen is generated at a current density of about 10 mA / cm ² after applying a potential of 17 hours and conducting electricity for 17 hours, which is comparable to the anode electrode catalytic properties of the glass substrate assembly with an iridium oxide film / tin oxide transparent electrode. I understand.

Further, the iridium oxide film / titanium assembly obtained by the present invention can be obtained by a known method using a glass substrate assembly having an iridium oxide film / tin oxide transparent electrode and an oxide manufactured by a reactive sputtering method. It can be seen that the effect over the iridium film is exhibited.

[Brief description of the drawings]

FIG. 1 is a graph (solid line) showing a time change of an oxygen generation reaction current density of an iridium oxide film / titanium assembly obtained in Example 1, and a mixed oxidation of iridium oxide and tantalum oxide obtained in Comparative Example 1. 4 is a graph (broken line) showing a time change of an oxygen generation reaction current density of a product / titanium joined body.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C25B 11/04 C25B 11/04 A 11/08 11/08 A 11/10 11/10 A (56) References -133599 (JP, A) JP-A-60-162800 (JP, A) JP-B-48-3954 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) C25F 1/00- 1/08 C25B 11/10 C23C 8/10-8/16

Claims (2)

(57) [Claims] 1. A method of manufacturing an iridium oxide film / metal assembly in which a composite film made of metal iridium and carbon is formed on a metal substrate and then heated and oxidized to make the composite film an iridium oxide film. A method for producing an iridium oxide film / metal assembly, wherein a surface electrolytic treatment of the metal substrate is performed by applying an AC voltage to the metal substrate in an aqueous sulfuric acid solution. 2. The method for producing an iridium oxide film / metal assembly according to claim 1, wherein the metal substrate is titanium.