Electro-Oxidation of Concentrated Ce(III) at Carbon Felt Anode in Nitric Acid Media

Abstract

Electro-oxidation of Ce(III) to Ce(IV) in parallel plate flow type electrolyzer divided with cation exchange membrane was carried out in nitric acid media at carbon felt anode under galvanostatic conditions. Carbon felt was used as an anode for its high specific surface area and high oxygen evolution overpotential. Pt coated Ti plates were used as cathode and anode current feeder. The oxidation of 1 mol·L −1 Ce(III) solution in 2 mol·L −1 HNO 3 was proceeding with a high current efficiency (92%) until about 80% of Ce(III) was oxidized. Then, oxygen evolution, accompanied by terminal voltage jump, took place, lowering current efficiency. Ce(III) was oxidized up to 90% with current efficiency of 62%. In this mode, strong carbon felt anode oxidation was observed. The wear out of carbon felt was 46% in six consequent runs (6 h of operation). After each run, carbon felt surface had to be renewed with slightly alkaline solution to remove carbon oxidation products and ensure regular operational conditions. When anode surface was blocked, oxygen evolution took place from the beginning of electrolysis due to higher actual current density. The wear out of carbon felt anode could be minimized by means of oxygen evolution prevention. In the case when electrolysis had been stopped before oxygen evolution started (at Ce(IV) conversion of about 80%), the wear out of anode was less than 2% during 6 consequent runs (4 h of operation).