Electrode for electrolytic processes and method for producing the same

Abstract

An electrode for electrolytic processes, in particular to an anode suitable for oxygen evolution in an industrial electrolytic process and a method of manufacturing thereof. More specifically, MMO coated titanium anode for electrochemical reaction used for oxygen evolution reaction (OER) in various applications such as electrowinning, electroplating, electrogalvanizing and electrolytic copper-foil production, and methods for manufacturing the anode.

1 . An electrode for electrolytic processes comprising:
 a valve metal substrate comprising a coating, the coating comprising a catalytic layer and a barrier layer interposed between the catalytic layer and the substrate,   the catalytic layer comprising a composition of metal oxides with a percent ratio of 17-42% Ta, 40-57% Ru, 19.5-26 Ir, and 0-9% Sn relative to the sum of Ta+Ru+Ir+Sn present in the catalytic layer,   the barrier layer comprising a composition of metal oxides with a percent ratio of 25-40% Ta, 0-16% Ru, 0-9% Ir, and 44-55% Sn relative to the sum of Ta+Ru+Ir+Sn present in the barrier layer,   wherein the coating is characterized by a diffusion area throughout in-between the barrier layer and the catalytic layer comprising oxides of metals that make up the barrier layer and the catalytic layer, the diffusion area comprising metal oxides with a percent ratio of 17-41% Ta, 17-39% Ru, 10-26% Ir and 14-37% Sn relative to the sum of Ta+Ru+Ir+Sn present in the diffusion area.   
     
     
         2 . The electrode according to  claim 1 , wherein
 the catalytic layer comprises the percent ratio of 17-21% Ta, 50-57% of Ru, 22-26% Ir and 2-7% of Sn relative to the sum of Ta+Ru+Ir+Sn present in the catalytic layer,   the barrier layer comprises the percent ratio of 34-40% Ta, 7-16% Ru, 4-9% Ir and 44-46% Sn relative to the sum of Ta+Ru+Ir+Sn present in the barrier layer, and   the diffusion area comprises the percent ratio of 21-34% Ta, 22-39% Ru, 12-26% Ir and about 14-31% Sn relative to the sum of Ta+Ru+Ir+Sn present in the diffusion area.   
     
     
         3 . The electrode according to  claim 1 , wherein the composition of metal oxides in the catalytic layer comprises the percent ratio of: 
       
         
           
                 
                 
                 
                 
                 
               
                     
                     
                 
                     
                   Ta At % 
                   Ru At % 
                   Ir At % 
                   Sn At % 
                 
                     
                     
                 
                     
                   18% 
                   57% 
                   24% 
                   2% 
                 
                     
                   21% 
                   56% 
                   22% 
                   2% 
                 
                     
                   17% 
                   56% 
                   26% 
                   2% 
                 
                     
                   18% 
                   50% 
                   25% 
                   7% 
                 
                     
                     
                 
             
                
                
                
               
               
                
                
                
                
                
               
            
           
         
         relative to the sum of Ta+Ru+Ir+Sn present in the catalytic layer. 
       
     
     
         4 . The electrode according to  claim 1 , wherein the composition of metal oxides in the barrier layer comprises the percent ratio of: 
       
         
           
                 
                 
                 
                 
                 
               
                     
                     
                 
                     
                   Ta At % 
                   Ru At % 
                   Ir At % 
                   Sn At % 
                 
                     
                     
                 
                     
                   37% 
                   16% 
                   4% 
                   44% 
                 
                     
                   34% 
                   13% 
                   9% 
                   45% 
                 
                     
                   40% 
                    7% 
                   7% 
                   46% 
                 
                     
                     
                 
             
                
                
                
               
               
                
                
                
                
               
            
           
         
         relative to the sum of Ta+Ru+Ir+Sn present in the barrier layer. 
       
     
     
         5 . The electrode according to  claim 1 , wherein the composition of metal oxides in the diffusion area comprises the percent ratio of: 
       
         
           
                 
                 
                 
                 
                 
               
                     
                     
                 
                     
                   Ta At % 
                   Ru At % 
                   Ir At % 
                   Sn At % 
                 
                     
                     
                 
                     
                   21% 
                   39% 
                   26% 
                   14% 
                 
                     
                   33% 
                   29% 
                   12% 
                   26% 
                 
                     
                   34% 
                   22% 
                   14% 
                   31% 
                 
                     
                     
                 
             
                
                
                
               
               
                
                
                
                
               
            
           
         
         relative to the sum of Ta+Ru+Ir+Sn present in the diffusion area. 
       
     
     
         6 . The electrode according to  claim 1 , wherein the valve metal substrate is niobium, zirconium, titanium or alloyed titanium. 
     
     
         7 . The electrode according to  claim 1 , wherein the roughness surface of the substrate is 2.0 to 10.0 μm in terms of the arithmetic average of the roughness profile (Ra). 
     
     
         8 . The electrode according to  claim 1 , wherein the catalytic coating loading is 2.0 to 20.0 g/m 2  in terms of total precious metals iridium and ruthenium. 
     
     
         9 . The electrode according to  claim 1 , wherein the barrier layer coating loading is 1.0 to 13.0 g/m 2  in terms of tin and tantalum. 
     
     
         10 . A method for manufacturing an electrode for electrolytic processes comprising:
 a. optionally, pre-treating a valve metal substrate to obtain a pre-treated substrate with a surface roughness of the substrate in the range of 2.0 to 10.0 μm in terms of the arithmetic average of the roughness profile (Ra);   b. mixing stannic hydroxyacetochloride (SnHAC) complex solution, tantalum solution and aqueous solution of 10 wt % acetic acid to obtain a Sn—Ta barrier layer solution;   c. preparing a precursor solution of Ru, Ir and Ta to obtain a catalytic coating solution of Ir—Ru—Ta;   d. applying the Sn—Ta barrier layer solution from step b) to the optionally pre-treated substrate, followed by drying, thermal decomposition treatment and cooling down to obtain a Sn—Ta barrier layer coated substrate;   e. optionally repeating step d) until reaching an overall loading of 1.0-13.0 g/m 2  in terms of Sn and Ta metals in the coated substrate;   f. applying the catalytic coating solution from step c) to the Sn—Ta barrier layer coated substrate, followed by drying, thermal decomposition treatment and cool down;   g. optionally repeating step f) until reaching an overall loading of the catalytic coating of 2.0 to 20.0 g/m 2  in terms of total precious metals Ir and Ru.   
     
     
         11 . The method according to  claim 10 , wherein the catalytic coating solution comprises 18-21 mol % iridium, 52-64 mol % ruthenium and 15-30 mol % tantalum. 
     
     
         12 . The method according to  claim 10 , wherein the barrier layer solution comprises oxides of tin and tantalum in a ratio of 70-90:30-10 mol % Sn:Ta. 
     
     
         13 . The method according to  claim 10 , wherein in step a) the pre-treating step is carried out first by sandblasting by alumina grit, followed by blasting with steel grit and then etching in aqueous solution of 20 wt % hydrochloric acid at boiling temperature for 20 minutes; after the etching, rinsing the substrate with deionized water and drying. 
     
     
         14 . The method according to  claim 10 , wherein in step b) the Sn—Ta barrier layer solution is obtained by mixing 1.65 M of stannic hydroxyacetochloride (SnHAC) complex solution, 120 g/L of tantalum solution and aqueous solution of 10 wt % acetic acid. 
     
     
         15 . The method according to  claim 10 , wherein in step c) the Ru precursor for the catalytic coating solution is RuCl 3  or RuHAC, Ir precursor is IrCl 3 , H 2 IrCl 6  or IrHAC, and Ta precursor is TaCl 5 . 
     
     
         16 . The method according to  claim 10 , wherein in step c) the precursor solution of Ru, Ir and Ta is obtained by mixing H 2 IrCl 6  solution, 20 wt % RuCl 3  solution, 120 g/L of tantalum solution and 10 wt % HCl. 
     
     
         17 . The method according to  claim 10 , wherein in steps d) and f) the drying temperature can be from 25° C. to 60° C. 
     
     
         18 . The method according to  claim 10 , wherein in steps d) and f) the thermal decomposition treatment is carried out in an electric furnace, at a temperature range of 480-530° C. for 10 to 20 minutes. 
     
     
         19 . An electrode obtained by a method comprising applying a barrier layer solution comprising oxides of tin and tantalum in a ratio of 70-90:30-10 mol % Sn:Ta to a valve metal substrate, followed by drying, thermal decomposition treatment and cooling down; thereafter applying a catalytic coating solution comprising 18-21 mol % iridium, 52-64 mol % ruthenium and 15-30 mol % tantalum to the barrier layer, followed by drying, thermal decomposition treatment and cooling down, wherein the electrode comprises a coating comprising a catalytic layer and a barrier layer interposed between the catalytic layer and the substrate.