Effect of In3+ ions on the electrochemical performance of the positive electrolyte for vanadium redox flow batteries

Influence of In 3+ ions on electrochemical performance of positive electrolyte for vanadium redox flow battery was investigated in this paper. The electrochemical activity and kinetics of V(IV)/V(V) redox couple can be enhanced by the addition of In 3+ ions, and the optimal concentration of In 3+ ions was found at 10 mM. At this condition, the oxidation peak current with 10 mM In 3+ ions is 46.6 mA at a scan rate of 20 mV s −1 , larger than that of pristine electrolyte (41.8 mA), and the standard rate constant is 6.53 × 10 −5 cm s −1 , 42 % larger than that of the pristine electrolyte (4.58 × 10 −5 cm s −1 ). The cell using electrolyte with 10 mM In 3+ ions was assembled, and the charge–discharge performance was evaluated, and the average energy efficiency increases by 1.9 % compared with the pristine cell. The improved electrochemical performance may be ascribed to that In 3+ ions change the hydration state of vanadium ions in electrolyte and promote charge transfer process.