The pseudocapacitance of nanocrystalline RuO2 with BET surface area of 42 m(2)g(-1) was evaluated using a RuO2 modified Glassy Carbon (RuO2/GC) thin film electrode. The charge storage behavior of the RuO2/GC thin film electrode was studied from fast to slow scan cyclic voltammetry between various potential windows. The utilization of the thin film electrode method for nanocrystalline RuO2 with known specific surface area allowed a semi-quantitative understanding of the electric double-layer capacitance (C-dl), adsorption related charge (C-ad), and the irreversible redox related charge (C-irr) per unit mass and surface area of RuO2. Comparison of the cyclic voltammograms between different voltage windows revealed that the contribution from C-irr is especially dominant below 0.4 V (versus RHE) at slow scan rates. (C) 2003 Elsevier Ltd. All rights reserved.