Ultrafine CoO nanolayer-shelled CoWP nanowire array: a bifunctional electrocatalyst for overall water splitting.

The development of bifunctional electrocatalysts based on highly efficient non-noble metals is pivotal for overall water splitting. Here, a composite electrode of CoO@CoWP is synthesized, where an ultrathin layer composed of CoO nanoparticles is grown on CoWP nanowires supported on a carbon cloth (CC). The CoO@CoWP/CC electrode exhibits excellent electrocatalytic activity and improved kinetics towards both the oxygen and hydrogen evolution reactions (OER and HER). The CoO@CoWP/CC electrode achieves a current density of 10 mA cm at a low overpotential of 269 mV for the OER and -10 mA cm at 118 mV for the HER in 1.0 M KOH solution. The voltage applied to a two-electrode water electrolyzer for overall water splitting, while employing the CoO@CoWP/CC electrode as both an anode and a cathode, in order to reach a current density of 10 mA cm, is 1.61 V, which is better than that for the majority of reported non-noble electrocatalysts. Moreover, the CoO@CoWP/CC electrode exhibits good stability over 24 h with slight attenuation. The electrode benefits from the enhanced adsorption of oxygen intermediates on CoO during the OER, the increased ability for water dissociation and the optimized H adsorption/desorption ability of CoWP nanowires during the HER. This study provides a feasible approach for cost-effective and high-performance non-noble metal bifunctional catalysts for overall water electrolysis.