Characterization of spinel Co 3O 4 and Li-doped Co 3O 4 thin film electrocatalysts prepared by the sol–gel route

Abstract

Spinel Co 3O 4 and Li-doped Co 3O 4 thin film electrocatalysts deposited on Pt and ITO/glass substrates were prepared by the sol–gel route from Co(II) sulfate precursor using dip-coating technique. Stoichiometry of undoped and Li + doped films (up to 10 mol% of Li +) prepared at 300 and 500°C, respectively, showed deficiency with Co(III) ions in the film structure. All films exhibited substantial electrical conductivity ( σ) which was slightly dependent on the type of the substrate. The roughness factor, RF, of electrodes was determined by cyclic voltammetry. Spinel oxide films prepared at lower temperatures (300°C) showed high surface area (RF∼700). The electrocatalytic properties were studied by different electrochemical methods in alkaline solutions. The results of electrochemical measurements in KOH indicated the formation of surface quasi-reversible redox couple, Co(IV)/Co(III), which is limited by a diffusion-controlled process. The oxygen evolution potentials pointed out remarkable performance of Co 3− x O 4 (300°C) and Li + doped Co 3− x O 4 (500°C) films. The reaction order with respect to [OH −] was found to be nearly 1.2. Durability testing of films in 5 M KOH at 70°C showed high long-term performance and structure stability of Li + doped Co 3− x O 4 (500°C) films.