The electrochemical properties and electrocatalytic performance of nanocrystalline oxide powders of the type IrxSn1-xO2 (0.2 <= x <= 1) have been examined. These oxides have been developed primarily as oxygen evolution electrocatalysts for proton exchange membrane (PEM) water electrolysers. The modified polyol method was used to prepare these oxides, by reducing precursors in ethylene glycol followed by thermal oxidation at 500 degrees C. The materials were characterised in 0.5 mol dm(-3) H2SO4 and PEM electrolytes by cyclic voltammetry, electrochemical impedance spectroscopy, and steady state polarisation measurements. Some comparisons were made between the electrochemical properties of the oxides in the different electrolytes. (c) 2005 Elsevier Ltd. All rights reserved.