Cathode for electrolytic evolution of hydrogen

Abstract

The invention relates to an electrode suitable for use as a cathode for hydrogen evolution in industrial electrolytic processes. The electrode comprises a metallic substrate, an internal catalytic layer containing rhodium and an external catalytic layer containing ruthenium.

1 . Electrode suitable for use as cathode in electrolytic processes comprising a metal substrate equipped with a catalytic coating, said catalytic coating comprising a platinum-containing internal layer directly contacting the substrate, at least one intermediate layer consisting of an oxide mixture containing 40-60% by weight of rhodium referred to the elements, an external layer of ruthenium oxide. 
     
     
         2 . The electrode according to  claim 1  wherein said metal substrate is made of nickel. 
     
     
         3 . The electrode according to  claim 1  wherein said at least one intermediate layer contains 10-30% by weight of palladium and 20-40% by weight of rare earths referred to the elements. 
     
     
         4 . The electrode according to  claim 3  wherein said rare earths consist of praseodymium. 
     
     
         5 . The electrode according to  claim 3  wherein the specific loading of platinum in said internal layer is 0.3 to 1.5 g/m 2 , the sum of specific loadings of rhodium, palladium and rare earths in said intermediate layer is 1 to 3 g/m 2  and the specific loading of ruthenium in said external layer is 2 to 5 g/m 2 . 
     
     
         6 . Method for manufacturing an electrode according to  claim 1  comprising the following steps:
 a) applying an acetic solution of Pt(NH3)2(NO3)2 to a metal substrate, with subsequent drying at 80-100° C. and thermal decomposition at 450-600° C.; 
 b) optionally repeating step a) until obtaining an internal catalytic layer with a specific loading of 0.3-1.5 g/m 2  of Pt; 
 c) applying an acetic solution containing a rhodium nitrate with optional addition of nitrates of palladium and of rare earths on said internal catalytic layer, with subsequent drying at 80-100° C. and thermal decomposition at 450-600° C.; 
 d) optionally repeating step c) until obtaining an intermediate catalytic layer with a specific loading of 1-3 g/m 2  as sum of Rh, Pd and rare earths; 
 e) applying an acetic solution containing Ru nitrosyl nitrate on said intermediate catalytic layer, with subsequent drying at 80-100° C. and thermal decomposition at 450-600° C.; 
 f) optionally repeating step e) until obtaining an external catalytic layer with a specific loading of 2-5 g/m 2  of Ru. 
 
     
     
         7 . The method according to  claim 6  wherein the temperature of said thermal decomposition of steps a), c) and e) ranges from 480 to 520° C. 
     
     
         8 . Electrolysis cell comprising an anodic compartment and a cathodic compartment separated by an ion-exchange membrane wherein the cathodic compartment is equipped with an electrode according to  claim 1 . 
     
     
         9 . Electrolyser for production of chlorine and alkali from alkali brine free of protecting polarisation devices comprising a modular arrangement of cells according to  claim 8 .