Mitigating capacity fading in aqueous organic redox flow batteries through a simple electrochemical charge balancing protocol

Abstract

Aqueous organic redox flow batteries (AORFBs) have recently been attracting much attention due to their potential utilization as a sustainable solution for stationary energy storage. However, AORFBs have still to face various challenges to become a competitive technology to other mature redox flow batteries. Fading of the energy storage capacity upon cycling leading to insufficient lifetime is likely the most pressing issue. Several processes are contributing to this issue. Among the capacity fading promoters, the existence of side reactions such as water splitting and reactions related to oxygen reduction triggers an imbalanced state of charge for the catholyte and anolyte. Herein, a simple electrochemical balancing procedure is proposed and successfully demonstrated through the restoration of the oxidation states of the two half-cell solutions. The results reveal that it is possible to mitigate and even revert the effects of such side reactions, developing a useful method for mitigating the capacity fading and prolonging the cycling performance of AORFBs. In the two case studies, the implementation of this simple charging procedure leads to a remarkable 20-fold reduction of capacity fading (% h−1). The protocol is a general approach for redox flow batteries, easily implementable and inexpensive.