Promoting the formation of Co (III) electrocatalyst with diamond anodes

Abstract In this work, the catalytic effect of electrode substrate on the electrochemical oxidation of cobalt (II) using boron doped diamond (BDD) anodes was studied. A significant increase of the Co (III) formation was observed in using BDD coatings on tantalum substrate (91.43% at around 90 min of galvanostatic electrolysis), with respect to the Si-BDD anode, which only attained a poorer Co (III) conversion (8.33%) after applying the same electric charge. Electrochemical impedance spectroscopy showed that the Ta/BDD electrode has a lower charge-transfer resistance for the Co (II)/Co(III) metallic pair and the process is controlled by diffusion of cobalt towards the electrode surface, due to its rapid adsorption at the interface. This was further confirmed by cyclic voltammetry (CV) where the electrodeposition of Co (II) on the electrode surface is obviously significant if we compare it with that of Si/BDD anode. This difference in the electrode behavior, caused by the substrate on which the diamond coating is deposited, opens a line of research to improve the efficiency of mediated electrolytic treatments based on the use of Co, with important industrial applications in the treatment of many pollutants including volatile organic compounds (VOCs).