Abstract: Exploration of cost-effective electrocatalysts for boosting the overall water-splitting efficiency is vitally important for obtaining renewable fuels such as hydrogen. Here, earth-abundant Co_xNi_1-xO nanowire arrays were used as a structural framework to dilute Ir incorporation for fabricating electrocatalysts for water splitting. Minimal Ir-incorporated Co_xNi_1-xO nanowire arrays were synthesized through the facile hydrothermal method with subsequent calcination by using Ni foam (NF) as both the substrate and source of Ni. The electrocatalytic water-splitting performance was found to crucially depend on the Ir content of the parent Co_xNi_1-xO nanowire arrays. As a result, for a minimal Ir content, as low as 0.57 wt%, the obtained Ir-Co_xNi_1-xO/NF electrodes exhibited optimal catalytic activity in terms of a low overpotential of 260 mV for the oxygen evolution reaction and 53 mV for the hydrogen evolution reaction at 10 mA cm^-2 in 1 mol L^-1 KOH. When used as bifunctional electrodes in water splitting, the current density of 10 mA cm^-2 was obtained at a low cell voltage of 1.55 V. Density functional theory calculations revealed that the Ir-doped Co_xNi_1-xO arrays exhibited enhanced electrical conductivity and low Gibbs free energy, which contributed to the improved electrocatalytic activity. The present study presents a new strategy for the development of transition metal oxide electrocatalysts with low levels of Ir incorporation for efficient water splitting.

Key words: Co_xNi_1-xO nanowire array, Iridium incorporation, Electrocatalyst, Water splitting, Overpotential