Electrode for electrolytic evolution of gas

Abstract

An electrode for evolution of gas in electrolytic processes having a substrate of valve metal and a catalytic coating having two layers. A first layer having oxides of valve metal, ruthenium and iridium and a second layer having one or more metals chosen from amongst elements of the platinum group.

1 . An electrode for gas evolution in electrolytic processes comprising
 a valve metal substrate and   a coating comprising
 a first catalytic layer formed on said substrate containing a mixture of iridium, ruthenium, tin and platinum or their oxides or combinations thereof, obtained from precursors containing said iridium, ruthenium and tin in the form of organometallic complexes, and 
 a second catalytic layer formed on said first catalytic layer containing platinum and tin or their oxides or combinations thereof, 
   wherein said tin of the said second catalytic layer is present in a decreasing concentration from the interface with said first catalytic layer and   wherein said platinum of the said first catalytic layer is present in a decreasing concentration from the interface with said second catalytic layer.   
     
     
         2 . An electrode for gas evolution in electrolytic processes comprising
 a valve metal substrate and   a coating comprising
 a first catalytic layer formed on said substrate containing a mixture of iridium, ruthenium, tin and platinum or their oxides or combinations thereof and 
 a second catalytic layer formed on said first catalytic layer containing platinum and tin or their oxides or combinations thereof, 
   wherein said first layer is obtained from a platinum-free first precursor solution comprising a mixture of iridium, ruthenium and tin, applied said substrate and subjected to a heat treatment,   wherein said platinum-free first precursor solution contains said iridium, ruthenium and tin in the form of organometallic complexes, and   wherein said second catalytic layer is obtained from a tin-free second catalytic composition containing platinum, applied said substrate and subjected to a heat treatment.   
     
     
         3 . The electrode according to  claim 1 , wherein said second catalytic layer contains Pt=48-96% in the form of metal, or its oxides, in molar percentage referred to the metal element. 
     
     
         4 . The electrode according to  claim 1 , wherein said second catalytic layer contains Pd=0-24% or Rh=0-24%, in the form of metal, or their oxides, or combinations thereof, in the form of metals or their oxides in molar percentage referred to the metal elements. 
     
     
         5 . The electrode according to  claim 1 , wherein said second catalytic layer contains Sn=4-12% in the form of metal or its oxides, in average molar percentage referred to the metal element. 
     
     
         6 . The electrode according to  claim 1 , wherein said iridium, ruthenium and tin oxides of said first catalytic layer are present in molar percentages Ru=24-34%, Ir=3-13%, Sn=30-70% referring to the metal elements. 
     
     
         7 . The electrode according to  claim 1 , wherein said first catalytic layer also contains titanium oxides in molar percentage Ti=30-40% referred to the metal element. 
     
     
         8 . The electrode according to  claim 1 , wherein said first catalytic layer contains Pt=3-10% in the form of metal or its oxides, in average molar percentage referred to the metal element. 
     
     
         9 . The electrode according to  claim 1 , wherein the valve metal substrate is selected from the group consisting of titanium, tantalum, zirconium, niobium, tungsten, aluminium, silicon, or their alloys. 
     
     
         10 . A method for the production of an electrode as defined in  claim 1 , comprising the following steps:
 applying to a valve metal substrate a platinum-free first solution comprising a mixture of iridium, ruthenium and tin, subsequently drying at 50-60° C. and carrying out decomposition of said first solution by heat treatment at 400-650° C. for a time of 5 to 30 minutes, wherein said first solution contains said iridium, ruthenium and tin in the form of organometallic complexes;   repeating the previous step until a desired specific load of noble metal is reached;   applying a tin-free second catalytic solution containing platinum and subsequently drying at 50-60° C. and carrying out decomposition of said second solution by heat treatment at 400-650° C. for a time of 5 to 30 minutes;   repeating the previous step until a desired specific load of noble metal is reached.   
     
     
         11 . The method according to  claim 10 , wherein the temperature of said thermal decomposition in steps a) and c) is between 480 and 550° C. 
     
     
         12 . (canceled) 
     
     
         13 . A cell for the electrolysis of solutions of alkaline chlorides comprising an anodic compartment and a cathodic compartment wherein the anodic compartment is equipped with the electrode according to  claim 1 . 
     
     
         14 . A cell for electrolysis according to  claim 13  wherein said anodic compartment and said cathodic compartment are separated by a diaphragm or an ion-exchange membrane. 
     
     
         15 . An electrolyzer for the production of chlorine and alkali from alkali chloride solutions comprising a modular arrangement of cells, wherein each cell is the cell according to  claim 13 . 
     
     
         16 . The electrode according to  claim 2 , wherein said second catalytic layer contains Pt=48-96% in the form of metal, or its oxides, in molar percentage referred to the metal element. 
     
     
         17 . The electrode according to  claim 2 , wherein said second catalytic layer contains Pd=0-24% or Rh=0-24%, in the form of metal, or their oxides, or combinations thereof, in the form of metals or their oxides in molar percentage referred to the metal elements. 
     
     
         18 . The electrode according to  claim 2 , wherein said second catalytic layer contains Sn=4-12% in the form of metal or its oxides, in average molar percentage referred to the metal element. 
     
     
         19 . The electrode according to  claim 2 , wherein said iridium, ruthenium and tin oxides of said first catalytic layer are present in molar percentages Ru=24-34%, Ir=3-13%, Sn=30-70% referring to the metal elements. 
     
     
         20 . The electrode according to  claim 2 , wherein said first catalytic layer also contains titanium oxides in molar percentage Ti=30-40% referred to the metal element. 
     
     
         21 . The electrode according to  claim 2 , wherein said first catalytic layer contains Pt=3-10% in the form of metal or its oxides, in average molar percentage referred to the metal element.