Catalysts made of earth-abundant elements for water splitting have attracted increasing attention in recent years. Herein we report that inexpensive cheap copper oxide thin film material can be used as an excellent electrocatalyst precursor for the oxygen evolution reaction (OER). Cuprous oxide (Cu2O) thin films were facilely electrodeposited on conductive fluorine doped tin oxide (FTO) substrates from a simple Cu(II) salt solution under a very low applied potential (-0.17 V or -0.23 V). Two kinds of morphologies (dendritic branching and cluster-like) of Cu2O were obtained just by altering the deposition potentials. Both Cu2O films can be used for OER, and the dendritic branching Cu2O material exhibits better performance. Under optimal conditions, OER was achieved under an onset potential at similar to 0.92 V (vs. Ag/AgCl) in 0.1 M borate solution at pH 9.2. A catalytic current density of similar to 0.1 mA/cm(2) required a low overpotential of similar to 430 mV using the electrodeposited Cu2O material under an optimal condition. The slope of the Tafel plot is similar to 59.9 mV/dec and the Faradaic efficiency was close to 93%. The samples were well characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). (C) 2015 Elsevier Ltd. All rights reserved.