From Water Oxidation to Reduction: Transformation from NixCo3–xO4 Nanowires to NiCo/NiCoOx Heterostructures

A homologous Ni–Co based nanowire catalyst pair, composed of NixCo3–xO4 nanowires and NiCo/NiCoOx nanohybrid, is developed for efficient overall water splitting. NixCo3–xO4 nanowires are found as a highly active oxygen evolution reaction (OER) catalyst, and they are converted into a highly active hydrogen evolution reaction (HER) catalyst through hydrogenation treatment as NiCo/NiCoOx heteronanostructures. An OER current density of 10 mA cm–2 is obtained with the NixCo3–xO4 nanowires under an overpotential of 337 mV in 1.0 M KOH, and an HER current density of 10 mA cm–2 is obtained with the NiCo/NiCoOx heteronanostructures at an overpotential of 155 mV. When integrated in an electrolyzer, these catalysts demonstrate a stable performance in water splitting.