1. Field of the Invention
The present invention relates to an electrode. More particularly, it relates to an electrode especially a cathode which is used in an electrolysis of an aqueous solution at a reduced cell voltage.
2. Description of the Prior Arts
Various anticorrosive electrodes have been used in electrolysis of aqueous solutions to obtain electrolyzed products such as electrolysis of an aqueous solution of an alkali metal chloride to obtain an alkali metal hydroxide and chlorine.
When an overvoltage of the electrode caused in an electrolysis of an aqueous solution such as an aqueous solution of alkali metal chloride is lowered, the electric power consumption can be reduced and the electrolyzed product can be obtained at lower cost.
In order to reduce a chlorine overvoltage of an anode, various studies have been made on the materials on the substrate and the treatments. Some of them have been practically employed.
It has been needed to use an electrode having a low hydrogen overvoltage and an anticorrosive characteristic since the diaphragm method for an electrolysis using a diaphragm has been developed.
In the conventional electrolysis of an aqueous solution of an alkali metal chloride using an asbestos diaphragm, iron plate has been used as a cathode.
It has been proposed to treat a surface of an iron substrate by a sand blast treatment in order to reduce a hydrogen overvoltage of the iron substrate (for example, Surface Treatment Handbook Pages 541 to 542 (Sangyotosho) by Sakae Tajima). However, the asbestos diaphragm method has disadvantages of a low concentration of sodium hydroxide as about 10 to 13 wt. % and a contamination of sodium chloride in an aqueous solution of sodium hydroxide. Accordingly, the electrolysis of an aqueous solution of an alkali metal chloride using an ion exchange membrane as a diaphragm has been studied developed and practically used. In accordance with the latter method, an aqueous solution of sodium hydroxide having high concentration of 25 to 40 wt. % may be obtained. When the iron substrate is used as a cathode in the electrolysis the iron substrate is broken by stress cracking in corrosion or a part of the iron substrate is dissolved in a catholyte because of high concentration of sodium hydroxide high temperature such as 80.degree. to 120.degree. C. in an electrolysis.
It has been preferable to use an alkali resistant anticorrosive substrate such as iron-nickel alloy, iron-nickel-chromium alloy-nickel, nickel alloy and chromium alloy as the substrate of the cathode. However, in the electrolysis of an aqueous solution of an alkali metal chloride using these cathodes, the hydrogen overvoltage is high and the electric power consumption is large and the cost for producing the electrolyzed products is high in comparison with those of the iron cathode. In the specification, the substrate means the material of the electrode and the etching treatment means the etching.