Crystalline Cobalt Oxide Films for Sustained Electrocatalytic Oxygen Evolution under Strongly Acidic Conditions

Earth-abundant materials capable of catalyzing the electrochemical decomposition of water into molecular hydrogen and oxygen are necessary components of many affordable water-splitting technologies. However, water oxidation catalysts that facilitate sustained oxygen evolution at device-relevant current densities in strongly acidic electrolytes have been limited almost exclusively to precious metal oxides. Here, we show that nanostructured films of cobalt oxide (Co₃O₄) on fluorine-doped tin oxide (FTO) substrates, made by first depositing Co onto FTO and heating in air at 400 °C to produce films having a robust electrical and mechanical Co₃O₄/FTO interface, function as active electrocatalysts for the oxygen evolution reaction (OER) in 0.5 M H₂SO₄. The Co₃O₄/FTO electrodes evolve oxygen with near-quantitative Faradaic yields and maintain a current density of 10 mA/cm² for over 12 h at a moderate overpotential of 570 mV. At lower current densities that require lower overpotentials, sustained oxygen production for several days and weeks can be achieved.