Electrochemical behavior of CoSb3 in sulfuric and oxalic acids over the potential range 0 to 40 V

The electrochemical behavior of pure Co, pure Sb, and CoSb3 has been investigated over a large anodic potential range (0 to 40 V) in two acids, i.e., oxalic acid or sulfuric acid at different concentrations (0.01 to 1 M). Potentiodynamic polarizations performed on CoSb3 plates reveal the possible formation of a passive layer between 1 and 3 V (vs SCE), on a passivation plateau. The oxidation of CoSb3 at 2 V in sulfuric and oxalic acids results in the growth of an anodic conversion layer. This coating is mainly made of a porous layer of amorphous antimony oxides due to dealloying of CoSb3. In the specific case of oxalic acid, rods of crystallized oxalates are tangled between the oxide sheets.