Abstract
This work demonstrates that anodic deposition of vanadium oxide (denoted as VO x ·nH 2 O) can be considered as the chemical co-precipitation of V 5+ and V 4+ oxy-/hydroxyl species and the accumulation of V 5+ species at the vicinity of electrode surface is the key factor for the successful anodic deposition of VO x · 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 V 4+ /V 5+ ratio near the electrode surface can be controlled by varying the applied potential, leading to different, three-dimensional (3D) nanostructures of VO x ·nH 2 O. The accumulation of V 5+ species due to V 4+ oxidation at potentials ≥0.4 V (vs. Ag/AgCl) has been found to be very similar to the phenomenon by adding H 2 O 2 in the deposition solution. The X-ray photoelectron spectroscopic (XPS) results show that all VO x ·nH 2 O deposits can be considered as aggregates consisting of mixed V 5+ and V 4+ oxy-/hydroxyl species with the mean oxidation state significantly increasing with the applied electrode potential. © 2010 Elsevier Ltd All rights reserved.