Electrochemical behaviour of FexCo3−xO4 with (x = 0, 1, 2 and 3) oxides thin film electrodes in alkaline medium

Spinel-type FexCo3−xO4 thin films with x = 0, 1, 2 and 3 were prepared, on stainless steel supports, using the thermal decomposition method at 400 °C. The X-ray diffraction patterns show the presence of a spinel-type structure with a low crystallinity. The electrochemical behaviour was investigated in 1 M KOH, using open-circuit-potential measurements and cyclic voltammetry. The studies allowed to observe the redox reactions occurring at the FexCo3−xO4 (x = 1 and 2) oxide surface, namely Fe3O4/Fe(OH)2 or Fe3O4/Fe2O3, Co3O4/CoOOH, Co(OH)2/CoOOH and CoO2/CoOOH by comparing the experimental data with those obtained for the Co3O4 and Fe3O4 films as well as with those referred to in the literature. The results show that iron ions play the major role in the solid-state surface redox transitions in the negative potential range, whereas the cobalt ions are the key species in the positive potential range. However, the contribution of each component, although small, has to be considered in both potential regions.