Preparation and characterisation of spinel type cobalt and rhodium oxide coatings on titanium

Co3O4 and Co2.95Rh0.05O4 layers on a Ti support were prepared by thermal decomposition of aqueous nitrate solutions at 673 K and characterised. The electrochemical behaviour was studied by cyclic voltammetry in 5 mol dm−3 KOH. The results showed that the presence of Rh in the spinel structure affects the surface of the coatings and the electric resistance of the substrate/coating interface. The electrodes were tested as anodes for oxygen evolution and the kinetics of the reaction was studied by means of steady-state measurements. The results revealed that the electrode performance towards the oxygen evolution reaction is enhanced by the presence of Rh due to the increasing specific surface area of the coating. Rh has no effect on the intrinsic electrocatalytic activity of the coatings and only geometric effects take place in addition to the decrease in resistivity across the Ti/Co2.95Rh0.05O4 interface.