CuxCo3−xO4/LaPO4-bonded Ni electrodes for oxygen evolution in alkaline solution: preparation, physicochemical properties, and electrochemical behavior

Abstract

Copper-cobalt oxide, prepared by thermal decomposition of nitrate precursors on a highly porous lanthanum phosphate-bonded nickel support, was investigated as an anode material for alkaline water electrolysis. Physicochemical characterization shows that this nonstoichiometric oxide possesses a spinel structure (Cu_0.9Co_2.1O₄) and that it is also highly porous. FTIR spectroscopy indicates that the oxide is not decomposed in 5 M KOH at room temperature. The highest electrocatalytic activity for the oxygen evolution reaction is obtained when the electrode is prepared at 300 °C from a solution containing 0.5 M Cu(NO₃)₂•2.5H₂O and 1.0 M Co(NO₃)₂•6H₂O, with a catalyst loading of 52 mg cm⁻². The activity is reduced when an excess of either Co or Cu is present in the spinel oxide film beyond the stoichiometric ratio of the precursors, probably due to some phase change. Cyclic voltammetry indicates that a quasi-reversible Co^IV/Co^III surface redox transition occurs prior to the onset of oxygen evolution; this process is diffusion controlled at low OH⁻ concentration and at high scan rate when [OH⁻] ≥ 1 M. In the negative potential domain, a Cu^II/Cu^I surface redox transition is observed. Keywords: copper-cobalt oxide, oxygen evolution, highly porous electrode, cyclic voltammetry.