Anode for electrolytic evolution of chlorine
An electrode suitable as chlorine-evolving anode in electrolytic cells and a method for obtaining thereof is provided. The electrode has a metal substrate coated with a catalytic composition made of thin layers based on oxides of tin, iridium and ruthenium and combines excellent characteristics of anodic potential and selectivity with respect to the reaction of chlorine evolution without resorting to the use of dopants such as platinum and palladium.
1. An electrode for evolution of gaseous products in electrolytic cells consisting of a metal substrate provided with a catalytic coating made up of layers,
each layer of said catalytic coating consisting of a mixture of oxides consisting of 55-70% by weight of tin, 5-10% by weight of iridium and 20-40% by weight of ruthenium referred to the metals,
each layer of the catalytic coating having an average thickness of 0.1 to 0.4 μm,
said catalytic coating having a total noble metal loading expressed as the sum of iridium and ruthenium referred to the metals of the coating of 2 to 8 g/m 2 ,
wherein the ratio Ir/Ru is 0.3 to 0.4 by weight referred to the metals of the catalytic coating,
wherein each layer of said catalytic coating is obtained by applying a solution containing precursors of tin, iridium and ruthenium in the form of acetic solution containing SnHAC, IrHAC and RuHAC to the metal substrate with subsequent drying at 50-60° C. and thermal decomposition at 450-600° C. until reaching a noble metal loading, and upon reaching the total noble metal loading applying a final heat treatment at 500-550° C. for 20-200 minutes.
2. The electrode according to claim 1 , wherein the noble metal loading of each layer of the catalytic coating expressed as the sum of iridium and ruthenium referred to the metals of the catalytic coating is 0.2 to 1.4 g/m 2 .
3. The electrode according to claim 1 , wherein the ratio Ir/Ru is 0.3 to 0.4 by weight referred to the metals of the catalytic coating.
4. The electrode according to claim 1 , wherein said catalytic coating consists of a mixture consisting of 55-65% by weight of tin oxide, 15-20% by weight of iridium oxide and 20-25% by weight of ruthenium oxide referred to the metals of the catalytic coating.
5. A method for manufacturing an electrode according to claim 1 comprising the execution of the following sequential steps on a metal substrate:
a) applying the acetic solution containing precursors of the components of said catalytic coating in the form of SnHAC, IrHAC and RuHAC to the metal substrate with subsequent drying at 50-60° C. and thermal decomposition at 450-600° C. until reaching a specific noble metal loading of 0.2 to 1.4 g/m 2 ;
b) repeating step a) until obtaining a catalytic coating with a specific noble metal loading of 2 to 25 g/m 2 ; and
c) finally heat treating at 500-550° C. for a time of 50 to 200 minutes.
6. The method according to claim 5 comprising an intermediate heat treatment at 500-550° C. for a time of 50 to 200 minutes carried out upon reaching the application of half the total loading of noble metal.
7. An electrolysis cell of alkali chloride solutions comprising an electrode according to claim 1 as chlorine-evolving anode.