In this paper, we investigate the electrocatalytic behavior and degradation characteristics of IrO2-based electrodes in Na2SO4 solutions containing C-1 compounds (CH3OH, HCHO and HCOOH). Decreases are generally observed in the electrochemically active area, electrochemical stability and durability of the electrodes in aqueous solutions in the presence of these organic substrates. The following sequence holds for the influence of C-1 compounds on the electrode properties (i.e. activity and stability): CH3OH > HCHO > HCOOH. The corrosion characteristics of electrode are studied by X-ray diffraction measurements. For the first time, the decomposition and dissolution of active oxide layers are quantitatively characterized from the decreases in cell volume of rutile-structured IrO2 crystallite and from the increases in texture coefficient of (0 0 2) planes, respectively, as a result of the accelerated lifetime tests. (C) 2005 Elsevier Ltd. All rights reserved.