Anode for oxygen evolution
An electrode for high overvoltage oxygen anodic evolution is described comprising a substrate of titanium or other valve metal, a first protective interlayer containing valve metal oxides, a second interlayer containing platinum or other noble metal, and an outer layer comprising tin, copper and antimony oxides. The electrode of the invention may be employed as anode in waste water treatment.
1. An anode for high overvoltage oxygen evolution, comprising a valve metal or ceramic substrate, a first interlayer of valve metal oxides applied to said substrate, a second interlayer consisting of platinum applied to said first interlayer, an outer layer consisting of oxides of tin, copper and antimony.
2. The anode of claim 1 wherein said valve metal substrate is made of titanium or titanium alloy.
3. The anode of claim 1 wherein said substrate of titanium alloy has a roughness profile controlled by a treatment comprising a sulfuric acid etching optionally preceded by sandblasting.
4. The anode of claim 1 wherein said first interlayer comprises titanium and tantalum oxides.
5. The anode of claim 1 wherein said second interlayer essentially consisting of platinum comprises 10 to 24 g/m 2 of platinum.
6. The anode of claim 1 wherein said outer layer comprises 5 to 25 g/m 2 of tin, 0.4 to 2 g/m 2 of antimony and 0.2 to 1 g/m 2 of copper.
7. The anode of claim 6 wherein tin is present in said outer layer in an amount not lower than 90% by weight of the overall metal content.
8. A method for the production of an anode for high overvoltage oxygen evolution of claim 1 , comprising applying a first interlayer based on valve metal oxides to a valve metal or ceramic substrate, applying a second interlayer essentially consisting of platinum to said first interlayer and applying an outer layer consisting oxides of tin, copper and antimony.
9. The method of claim 8 wherein said substrate is a titanium alloy substrate with a controlled roughness profile obtained by sandblasting and subsequent sulfuric acid etching.
10. The method of claim 8 wherein said first interlayer is applied by means of at least one method selected between spraying, brushing and rolling starting from a solution of chlorides of titanium and tantalum, with subsequent thermal decomposition at a temperature comprised between 450 and 600° C.
11. The method of claim 8 wherein said second interlayer essentially consisting of platinum is applied by thermal decomposition of a solution containing hexachloroplatinic acid at a temperature comprised between 400 and 600° C.
12. The method of claim 8 wherein said outer layer is applied in multiple coats starting from a solution containing chlorides of tin, antimony and copper, with subsequent thermal decomposition at a temperature between 450 and 600° C.
13. In an electrochemical process comprising the anodic evolution of oxygen at potential above 2 V (NHE) the improvement comprising using an anode of claim 1 .
14. The process of claim 13 comprising the industrial treatment of waters.
15. The process of claim 14 wherein said treatment comprises the elimination of organic molecules from waste waters.