Study of the electrochemical performance of VO2+/VO2 + redox couple in sulfamic acid for vanadium redox flow battery

The present work was performed in order to evaluate sulfamic acid as the supporting electrolyte for VO2+/VO2 (+) redox couple in vanadium redox flow battery. The oxidation process of VO2+ has similar electrochemical kinetics compared with the reduction process of VO2 (+). The exchange current density and standard rate constant of VO2+/VO2 (+) redox reaction on a graphite electrode in sulfamic acid are determined as 7.6 x 10(-4) A cm(-2) and 7.9 x 10(-5) cm s(-1), respectively. The energy efficiency of the cell employing sulfamic acid as supporting electrolyte in the positive side can reach 75.87 %, which is adequate for redox flow battery applied in energy storage. The addition of NH4 (+) to the positive electrolyte can enhance the electrochemical performance of the cell, with larger discharge capacity and energy efficiency. The preliminary exploration shows that the vanadium sulfamate electrolyte is promising for vanadium redox flow battery and is worthy of further study.