NaCl as an effective additive for enhancing the electrochemical activity of positive electrolyte for vanadium redox flow battery

Abstract

The concentration of electrolyte for vanadium battery is related to its energy density and total energy storage. Thus, the preparation of vanadium electrolyte with high concentration can contribute to improve the energy storage of vanadium battery. Nevertheless, the low solubility of V(Ⅴ) and the low stability at relatively high temperatures limit the further enhancement of the concentration of electrolyte. Thus, it is of importance to keep stability of V(Ⅴ) and enhance the electrochemical activity of electrolyte. Besides, adding additives is an important way to improve the ion stability and electrochemical activity of vanadium battery electrolyte. In this paper, several common chlorides of metal ions are chosen as additives to add into the positive electrolyte of vanadium battery. In addition, the electrochemical activity, stability and dynamic behaviors of the electrolyte were studied using the electrochemical technology such as cyclic voltammogram and electrochemical impedance spectroscopy, and so on. The results showed that the addition of NaCl, FeCl₃ and MgCl₂ as additives could obviously enhance the electrochemical activity of the positive electrolyte for vanadium battery. Compared with other additives, on the premise of not affecting the stability of the electrolyte, the electrolyte with 0.02 mol/L NaCl as an additive had the highest redox peak current. Moreover, the diffusion coefficient of the active substance is more than 2 times than that of the electrolyte without additive. Hence, the electrolyte with 0.02 mol/L NaCl as an additive displays the highest electrochemical activity.