JPS6017086A - Cathode for aqueous solution electrolysis and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Industrial Field of Application] A cathode for the electrolysis of aqueous alkaline solutions and aqueous solutions of alkali chloride to obtain hydrogen, comprising a carrier made of nickel or nickel-coated steel; The present invention relates to a layer that at least partially covers the surface of a carrier and includes a platinum group metal.

[Conventional technology]

For the electrolysis of aqueous solutions at temperatures below room temperature, mixtures containing oxides of the group of platinum metals and of the group of passivatable metals, such as 30 molar ruthenium oxide and 70 molar titanium oxide, are used. Titanium anodes coated with a mixture of are known (German Patent Application No. 1,671,422). This anode has a relatively small overvoltage and is easy to handle because the electrode spacing remains unchanged during the electrolysis process. In this electrolytic treatment, it is also known that the cathode is generally made of steel, nickel or nickel and is coated with metallic ruthenium (German Patent Application No. 2734084). In that case, the metal layer covering the carrier is produced by electrolysis or CVD methods. In other methods, ruthenium-containing layers are produced on the carrier by electroplating or by pyrolysis of salt-containing precipitates (DE 2811472). In that case, the surface of the carrier is coated with a ruthenium compound, e.g. ruthenium hydroxide,
It is coated with a solution or suspension of ruthenium chloride, ruthenium oxide or ruthenium sulfide, a solvent or dispersion medium is deposited, and the compound is decomposed by heating to about 12001Z' in a non-oxidizing atmosphere. For the production of fuel cells that are not used in electrolysis processes, it is known to provide a layer containing metallic ruthenium and spinel on the surface of the cathode.

[Problem that the invention seeks to solve]

Coating the cathode carrier with ruthenium metal is not preferred because the hydrogen overvoltage increases with prolonged use of the cathode (4) and under many conditions the overvoltage becomes relatively too large. The problem to be solved by the present invention is therefore to obtain a coated cathode which is stable with respect to electrolytes and electrolysis products and which has a small overpotential with respect to hydrogen.

[Means and effects for solving the problem] The above-mentioned problem is solved according to the invention by a cathode comprising a layer comprising ruthenium oxide and nickel oxide and consisting of a plurality of sublayers.

It is known to coat anodes consisting of titanium supports with platinum metal oxides alone or in mixtures with other oxides. It has been found that anodic coatings are of no use for the cathode,9 and therefore the cathode is coated with metallic platinum or an element of the platinum group and the first coating layer of the electrode is an oxide or other salt type compound. It has been found that supports made of nickel or nickel-coated steel coated with ruthenium oxide and nickel oxide have lower overpotentials to hydrogen and better stability than metal-coated cathodes.

The carrier of the cathode according to the invention consists of a porous or massive plate, rod or tube of nickel or nickel-coated steel, depending on the predetermined conditions of the electrolytic treatment. The layer of ruthenium oxide and nickel oxide deposited on the surface of the carrier and at least partially covering the surface consists of a plurality of sublayers, these sublayers together forming a coating.

According to an advantageous embodiment of the invention, the proportions of the oxides in the individual sublayers are different. By dividing the coating into several partial layers, very good adhesion and at the same time a long service life are achieved. The partial layer adjacent to the carrier contains more Nimotsu oxide than ruthenium oxide, and the partial layer facing the electrolyte is preferably oxidized. Partial layers with a content of nickel oxide of 70 to 95% and ruthenium oxide of 30 to 5% and nickel oxide of 5 to 25% and ruthenium oxide of 95 to 75% are preferred.

The thickness of the coating is 1 to 10 μm, in particular 2 to 5 μm, and the number of partial layers is 3 to 5, so that the cross-sectional thickness of one partial layer is approximately 0.2 to 3 μm. In this range the cathodic activity is particularly good together with good mechanical stability of the layer.

To produce the cathode, a carrier made of nickel group, nickel-plated steel is coated with a solution containing nickel and ruthenium salts, such as ethanolic hydrochloride solutions of nickel nitrate and ruthenium chloride. The solvent is removed by drying and the carrier is dried in air from about 450 to 55
Heated to 0C. In that case, a layer consisting of nickel oxide and ruthenium oxide is formed, the thickness of which is proportional to the amount of solution applied to the carrier surface. This process is repeated 3 to 5 times, resulting in a layer consisting of 3 to 5 partial layers.

〔Example〕

The invention will now be explained by means of diagrams and examples.

Example 1 A commercially available sandblasted nickel plate 1° thick and 50 mm x 50 cm in size was coated with the following solution. The composition of this solution consists of 15.6 m9 of Ni(NOs)2 and 26 mg of RuCQ3, which is 80 wt% N in 75 μC ethanol and 50 μα concentrated hydrochloric acid.
Corresponds to i/20 Juuka %Ru. The board was dried and heated to 500C in atmospheric oxygen in a Matsufuru furnace with a stop time of 10 minutes.

To create the second layer, 7.8 m9 of N i (NO3
)2 and 15m9 of RuCQ3 was applied, which solution contained 75μα of ethanol and 25μα
25 wt% Ni/75 wt% R in hydrogen chloride produced by
Corresponds to u. The plate was dried and heated as described above.

Then, 3.9μ of Ni(NO3)2 and 20m
9 with RuCff3, i.e. 11 wt% Ni/
A third layer consisting of a solution corresponding to 89% RH by weight was applied and heat treated.

Example 2 An expanded metal grid made of V4A steel was sandblasted and nickel plated in Watts electrolyte, the layer thickness being approximately 5 μm. on a nickel-plated carrier,
As described in Example 1, three partial layers of nickel oxide and ruthenium oxide were applied.

The cathode voltage in Examples 1 and 2 was measured as a function of current density in a 20°C aqueous solution of NaOH at 7oC. The results are shown in FIG.

In the figure, the ○ mark indicates Example 1, and the △ mark indicates Example 2. The reference electrode was a saturated calomel electrode. For comparison, sandblasted special steel plate (1) and nickel plate (2).

The small potential of the cathode according to the invention, which rises relatively slowly with increasing nickel density coated by West Gold Plate (3) and Example 1, requires no particular explanation. 51kA/
As the measurement results in the case of a current density of m2 show, the potential is practically independent of the operating time (FIG. 3).

〔Effect of the invention〕

According to the present invention, it is possible to obtain the effects of low overvoltage with respect to hydrogen, good stability, and long life.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the cathode potential of the cathode according to the present invention as a function of current density, FIG. 2 is a characteristic diagram showing the cathode potential of cathodes made of various materials as a function of current density, and FIG. FIG. 3 is a characteristic diagram showing the cathode potential of the cathode according to the invention as a function of time; DESCRIPTION OF SYMBOLS 1... Special steel plate, 2... Nickel plate, 3... Platinum plate, 4... Nickel cathode coated according to Example 1. Ni! n 2 style Shihi (kA-) 1jEi:2 Electrical technique completion (kA,,1

Claims (1)

[Claims] ■) A cathode for aqueous electrolysis comprising a carrier made of nickel or nickel-coated steel and a layer containing platinum metal that at least partially covers the surface of the carrier, the layer comprising ruthenium oxide and A cathode for aqueous electrolysis, characterized by comprising a plurality of partial layers containing nickel oxide. 2) The cathode according to claim 1, characterized in that the component ratios of the oxide in the individual partial layers of the layer are different. 3) A cathode according to claim 1 or 2, characterized in that the partial layer adjacent to the carrier comprises 7 to 95% by weight of nickel oxide and 30 to 5% by weight of ruthenium oxide. nickel oxide and 95 to 75% by weight of ruthenium oxide.
The cathode according to any one of Items 1 to 3. 5) A cathode according to any one of claims 1 to 4, characterized in that the layer has a thickness of 1 to 10 μm. 6) A cathode according to any one of claims 1 to 5, characterized in that the layer consists of 3 to 5 partial layers. 7) A carrier made of nickel-group, nickel-plated steel is coated with a solution containing nickel salts and ruthenium salts, dried and heated to 450 to 550 C in air, and this process is repeated 3 to 5 times. A method for producing a cathode for aqueous electrolysis, characterized by: