Influence of several additives on stability and electrochemical behavior of V(V) electrolyte for vanadium redox flow battery

•The stability of V(V) solution with additives could be significantly improved.•The concentration of V(V) solution with additives remained high levels after 30 days.•The electrochemical activity was improved compared to the pristine solution.

Several compounds have been employed as additives of the V(V) electrolyte for vanadium redox flow battery (VRB) to improve its stability and electrochemical activity. Stability of the V(V) electrolyte with and without additives was investigated with ex-situ heating/cooling treatment over a wide temperature range of −5 °C to 60 °C. It was observed that methyl orange (MO), Triton X-100 (OP), sodium ligninsulfonate (SL), sodium dodecyl sulfate (SDS) and polyvinyl alcohol (PVA) could significantly improve the stability of the V(V) electrolyte at a wide range of temperature. Their electrochemical behavior in the V(V) electrolyte were further studied by cyclic voltammetry (CV), steady state polarization and electrochemical impedance spectroscopy (EIS). The results showed that the electrochemical activity, including the reversibility of electrode reaction, the diffusivity and polarization resistance of V(V) species and the feasibility of charge transfer of V(V)/V(IV) for the V(V) electrolyte with these additives was all improved compared with the pristine solution.