In this present study, we report tuning the catalytic activity in heterogeneous copper oxide (CuO) material as an efficient catalyst in 1.0 M KOH for the oxygen evolution reaction (OER) with low catalyst loading. The CuO materials were facilely synthesized by a simple molten salt method at a high temperature and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area analysis. The catalytic water oxidation activity is affected by many factors, such as the catalyst morphologies, electronic double-layer capacitance, and the conductivity. Under optimal conditions, the CuO material prepared at 900 degrees C showed the nanosheets structure with more exposed catalytic active sites and demonstrated high catalytic performance for OER with a low overpotential of only 420 mV to achieve 10 mA/cm(2) and 520 mV to achieve 40 mA/cm(2), respectively. Furthermore, when CuO nanosheets are mixed with multi-walled carbon nanotubes (MWCNTs), the catalyst loading can be greatly decreased from 0.7 mg/cm(2) to 0.14 mg/cm(2) and the overpotential for 40 mA/cm(2) is also lowered to 470 mV. (c) 2018 Elsevier Ltd. All rights reserved.