This work demonstrates that anodic deposition of vanadium oxide (denoted as VOx nH(2)O) can be considered as the chemical co-precipitation of V5+ and V4+ oxy-/hydroxyl species and the accumulation of V5+ species at the vicinity of electrode surface is the key factor for the successful anodic deposition of VOx nH(2)O at a potential much more negative than the equilibrium potential of the oxygen evolution reaction (OER) The results of in situ UV-vis spectra show that the V4+/V5+ ratio near the electrode surface can be controlled by varying the applied potential leading to different three-dimensional (3D) nanostructures of VOx nH(2)O The accumulation of Vs species due to V4+ oxidation at potentials >= 0 4 V (vs Ag/AgCl) has been found to be very similar to the phenomenon by adding H2O2 in the deposition solution The X-ray photoelectron spectroscopic (XPS) results show that all VOx nH(2)O deposits can be considered as aggregates consisting of mixed V5+ and V4+ oxy-/hydroxyl species with the mean oxidation state significantly increasing with the applied electrode potential (C) 2010 Elsevier Ltd All rights reserved