RuO2/NiO mixed oxide electrodes prepared by thermal decomposition were examined as potential water oxidation catalysts. Addition of just 10 mol% RuO2 to a NiO electrode was found to decrease the oxygen evolution reaction (OER) onset potential by 20% with increasing additions having significantly diminishing returns. The OER current densities for the RuO2/NiO electrode were found to increase when preconditioned by application of prolonged polarization regimes with the Tafel slope also decreasing when conditioned. NiO prepared by thermal decomposition was found to behave in a similar manner to other nickel oxides prepared using different methodologies and we propose a similar OER mechanism based on the kinetic data obtained using the surfaquo group concept. A dual bather model was used to rationalize the fractional reaction order of ca. 0.5 observed for RuO2. (C) 2014 The Electrochemical Society. All rights reserved.