The V5+ electrolyte solution from Vanadium Redox Flow Batteries was studied by variable temperature O-17 and V-51 Nuclear Magnetic Resonance (NMR) spectroscopy and density functional theory (DFT) based computational modeling. It was found that the V5+ species exist as hydrated penta co-ordinated vanadate ion, i.e. [VO2(H2O)(3)](1+). This hydrated structure is not stable at elevated temperature and change into neutral H3VO4 molecule via a deprotonation process and subsequently leading to the observed V2O5 precipitation in Vs electrolyte solutions. (C) 2010 Elsevier B.V. All rights reserved.