Carbon electrodes improving electrochemical activity and enhancing mass and charge transports in aqueous flow battery: Status and perspective

The aqueous flow battery that possesses the superior capacity balance between supply and demand is deemed as one of the most promising large-scale energy storage systems. As the critical place for the redox reactions and mass and charge transports in flow batteries, the pristine carbon electrode usually exhibits high kinetic irreversibility and low electrochemical activity, lowering the energy efficiency and operating current density. Developing electrodes with the features of high electrochemical activity, porous structure, and electrical conductivity is urgently required, and thus, great efforts have been devoted to designing high-efficient electrodes for the high performance and even large-scale commercialization of aqueous flow batteries in recent years. In this review, based on the understanding of the mechanisms for mass and charge transport and redox reaction, various electrodes, such as chemical substance modified electrodes and physical structure engineered electrodes, are reviewed systematically. The modification, characterization and evaluation of electrodes are also summarized in detail. Finally, the scientific challenges and future prospects of electrodes are overviewed. This review can provide guidance and perspective for developing next-generation electrodes in aqueous flow batteries.