IrOx and Ir(0.7)Ru(0.3)Ox nanosized materials of similar crystallite size (5 nm) were prepared for application as oxygen evolution electrocatalysts in solid polymer membrane water electrolysers (PEMWEs). The physico-chemical properties of the catalysts were characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) and X-ray-Photoelectron Spectroscopy (XPS). Particular efforts were addressed to tailor the crystallographic characteristics and the surface properties. The electrochemical properties were investigated in an electrolysis cell, based on Nafion 115 and 30% Pt/C as cathode catalyst, by using linear sweep voltammetry, electrochemical impedance spectroscopy and Tafel curves. The Ir(0.7)Ru(0.3)Ox-based electrocatalyst showed a performance of 3.2 A cm(-2) at 1.85 V at 90 degrees C which corresponds to a voltage gain of 0.1 V as compared to the IrOx catalyst at the same current density. Alternatively, an increase in current density of 0.6 A cm(-2) is achieved at 90 degrees C and 1.85 V for the IrRuOx anode. A similar Tafel slope with a decrease of charge transfer resistance for IrRuOx compared to IrOx would indicate the same mechanism for these materials and higher intrinsic activity for the mixed oxide. (C) 2014 Elsevier B.V. All rights reserved.