MECHANISTIC STUDIES OF THE OXYGEN REACTIONS ON NICO2O4 SPINEL AND THE HYDROGEN EVOLUTION REACTION ON AMORPHOUS NI-CO SULFIDE

The mechanism of the oxygen evolution and reduction reactions on teflon-bonded NiCo2O4 spinel has been examined several times, mainly because of the potential application of this material in water electrolysers and fuel cells. However, some controversy still remains. This work presents the results of electrochemical studies of the oxygen evolution and reduction on NiCo2O4 spinel in alkaline solutions and a proposal for the mechanisms involved. Kinetic parameters were obtained by steady state polarization experiments, complemented with cyclic voltammetry to examine the surface of the catalyst. The role of the oxidation state of the surface on the mechanism of the oxygen evolution reaction is examined. Results of the study of the hydrogen evolution reaction on amorphous Ni-Co sulphide in alkaline solutions are also presented. This material showed an improved performance in comparison with other catalysts and a mechanism for the reaction is proposed on the basis of the experimental parameters.