The redox behavior of a decavanadium complex [(V=O)(10)(mu(2)-O)(9)(mu(3)-O)(3)(C5H7O2)(6)] (1) was studied using cyclic voltammetry under acidic and basic conditions. The reduction potential of V(V) was found at less positive potentials for higher pH electrolyte solutions. The oxygen reduction at complex I immobilized on a modified electrode was examined using cyclic voltammetry and rotating ring-disk electrode techniques in the I M KOH solutions. On the basis of measurements using a rotating disk electrode (RDE), the complex I was found to be highly active for the direct four-electron reduction of dioxygen at -0.2 V versus saturated calomel electrode (SCE). The complex I as a reduction catalyst of O-2 with a high selectivity was demonstrated using rotating ring-disk voltammograms in alkaline solutions. The application of complex I as an oxygen reduction catalyst at the cathode of zinc-air cell was also examined. The zinc-air cell with the modified electrode showed a stable discharge potential at approximately I V with discharge capacity of 80 mAh g(-1) which was about five times larger than that obtained with the commonly used manganese dioxide catalyst. (C) 2004 Published by Elsevier B.V.