Several ionic organic compounds as positive electrolyte additives for a vanadium redox flow battery

Several ionic organic compounds have been employed as additives of the V( v ) electrolyte for a 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 an ex situ heating/cooling treatment over a wide temperature range of −5 °C to 60 °C. It was found that cationic organic compounds could significantly improve the stability of the V( v ) electrolyte over a wide range of temperatures. Their electrochemical behavior in the V( v ) electrolyte was further studied by cyclic voltammetry (CV) and steady state polarization. The results showed that the electrochemical activity, including the reversibility of the electrode reaction, the diffusivity of V( v ) species, polarization resistance of V( v ) species, and the flexibility of charge transfer for the V( v ) electrolyte with these additives were all improved compared with the pristine solution. The VRB employing the positive electrolyte with cationic organic compounds as additive exhibited excellent charge-discharge behavior with an average energy efficiency of more than 80% at a current density of 20 mA cm −2 . XPS spectra illustrated that the addition of CHPTAC introduced more oxygen-containing and nitrogen-containing functional groups, which improved the electrochemical performance and cycling stability of the VRB. Several ionic organic compounds have been employed as additives of the V( v ) electrolyte for a vanadium redox flow battery (VRB) to improve its stability and electrochemical activity.