The present work seeks to understand the chemical structure and solvation thermodynamics of aqueous vanadium cations commonly employed in vanadium redox flow batteries. First principles based electronic structure calculations were performed to obtain the hydration structure and partial charges distributions of the cations in bulk water. The thermodynamics of solvation was determined within the context of a quasi-chemical theory of solution. The free energies of solvation for the V2+, V3+, VO2+, and VO2+ cations were computed to be: -440.0, -1018.8, -457.2, and -184.4 kcal/mol, respectively, which agree well with available experimental values. (C) 2013 Elsevier B.V. All rights reserved.