Study of vanadium(IV) species and corresponding electrochemical performance in concentrated sulfuric acid media

► Two new UV/Vis absorbance peaks are found in V(IV) sulfuric acid solutions. ► We give the structural information on the new corresponding V(IV) species. ► Reaction route is given with increasing sulfuric acid and V(IV) concentrations. ► We find V(IV) species corresponding to the reversible electrochemical reaction. ► A mixed-valence intermediate is invoked in the reversible reaction.