The effect of Zn2+ on the positive electrolyte for all-vanadium redox flow battery

In this work, the effects of Zn 2+ on the electrochemical activity of positive electrolyte were researched by cyclic voltammetry(CV), AC impedance. The results of CV showed that the positive electrolyte containing 2 wt% Zn 2+ as additive had the best electrochemical activity. Compared with the electrolyte without any additive, the electrolyte with 2 wt% Zn 2+ obviously enhanced electrochemical activity and reversibility of Farady reaction. In addition, the kinetic study of the mass transfer process indicated that the diffusion coefficient obviously increased. Besides, the results of electrochemical impedance spectroscopy implied that the internal charge transfer resistance of the electrolyte electrochemical system containing Zn 2+ as an additive was significantly reduced. This indicated that the charge transfer was significantly accelerated, which was beneficial to the improvement of the electrochemical activity. Moreover, the study of the electrolyte stability showed that the electrolyte containing Zn 2+ had superior stability yet after 30 cycles’ scanning. • Zn 2+ was firstly used as an additive for the positive electrolyte of all vanadium battery. • The effect of the additive on positive electrolyte was evaluated. • The possible reasons which resulted in better electrochemical performance were analyzed.