Electrocatalytic Activity of Oxygen-Functionalized Carbon Electrodes for Vanadium Redox Flow Batteries from Free-Energy Calculations

Detailed atomistic understanding of the vanadium redox reactions taking place at electrode/water interfaces is key for improvement of the power density of vanadium redox flow batteries. In this work, we employ ab initio molecular dynamics-based metadynamics simulations to examine V2+/V3+ and VO2+/VO2+ redox reactions at the oxygen-functionalized graphite (112̅0) surface contrasting the behavior of O–C═O and C═O groups. By evaluating free-energy barriers, we reveal that the kinetics of adsorption and desorption processes for every vanadium ion is more favorable in the case of O–C═O. We also find that interfacial VO2+/VO2+ transformations should be more rapid than those observed for the V2+/V3+ couple, with the V3+ desorption being the rate-limiting step of the overall process. The obtained results suggest that increasing the content of O–C═O groups on carbon-based electrodes should help enhance the power density of vanadium redox flow batteries.