Electrocatalytic Activity of Modified Graphite Felt in Five Anthraquinone Derivative Solutions for Redox Flow Batteries

Redox flow batteries have received wide attention because of their unique advantages such as high efficiency, long cycle life, low operating cost, and independent adjustment of energy power. In this study, five types of anthraquinone derivative organic redox couple were selected, and the surfaces of graphite felt were modified. When the number of functional groups is increased or the substitution position is closer to the carbonyl (C═O) groups, a more pronounced hindrance for the C═O reaction on the benzene ring is observed; thus, the electrochemical performance and reversibility decreases. Sodium 9,10-anthraquinone-2-sulfonate solution is the best organic redox couple in terms of both reversibility and electrochemical performance. It was also found that all the surface treatment methods of graphite felt are beneficial for improving their electrochemical performances. All these superior results demonstrate that the graphite felt treated under air exposure at 550 °C for 3 h exhibited the best electrochemical performance, which might be attributed to the increase in the content of C–OH functional groups.