The chemical and electrochemical equilibria in the V–H2O system, the potential–pH diagram for vanadium considering different vanadium oxides

Previous studies concerning chemical and electrochemical equilibria of vanadium in aqueous medium were reviewed. Thermodynamic data on vanadium oxides and aqueous species, including standard Gibbs energies of formation, standard electrode potentials, and equilibrium constants of hydrolysis reactions, were collected and analysed. The data were checked for consistency. The activity–pH diagrams for vanadium aqueous species of different oxidation states and the potential–pH diagram for the V–H 2 O system were revised, and the thermodynamic stability of different mixed-valence vanadium oxides and polyoxovanadates was discussed. The presented thermodynamic diagrams complement the previous studies by taking into account different vanadium oxides, vanadium cations, and polyoxovanadates. It was revealed that vanadium oxides in intermediate oxidation states are thermodynamically stable in the range of the electrochemical stability of water and affect the stability of polyoxovanadates. The role of thermodynamic stability of polyoxovanadates in their practical application and the ways of their stabilization are discussed.