Copper oxide (CuO) is a quite cheap and abundant material but there are very few reports of using it as water oxidation catalyst (WOC). In this present study, we report for the first time that CuO nanomaterials synthesized from simple copper salts can be used as WOCs with good activity. CuO materials with different morphologies (microspheres, nanosheets, nanowires) were facilely synthesized without using any template or surfactants. The influence of different morphologies and sizes on the catalytic activity toward oxygen evolution was investigated. Among the four kinds of samples tested, CuO nanowire material exhibited the lowest overpotential for water oxidation and CuO microsphere material had the best catalytic current densities from 1.10-1.40 V. Based on the CV scans, in optimal conditions for these nanomaterials, water oxidation can be achieved under an onset potential of similar to 0.90 V at pH 9.2. The slope of the Tafel plot is 54.5 mV/dec. The Tafel plot also shows appreciable catalytic current at eta = 340 mV (onset) and that a current density of similar to 0.1 mA/cm(2) required an overpotential at eta = 430 mV. The Faradaic efficiency was measured to be >95%. The CuO samples were further characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). (C) 2015 Elsevier Ltd. All rights reserved.