Tactical Surface Modification of a 3D Graphite Felt as an Electrode of Vanadium Redox Flow Batteries with Enhanced Electrolyte Utilization and Fast Reaction Kinetics

Three-dimensional porous carbon materials have great importance as electrode materials for vanadium redox flow batteries due to electrochemical stability over a wide potential window and low cost. However, sluggish electrode kinetics toward vanadium redox reactions makes electrode treatment vital before its use in a vanadium redox flow battery. Researchers have used different routes to modify the graphite electrode surface. This article presents a very simple (and known) but tactical procedure to treat a graphite felt. The modified electrode possesses large surface area having well-developed uniform pore structures and abundant oxygen-rich surface functional groups (11.2%), which offers a significant reduction in peak separation potential and charge-transfer resistance with a noteworthy improvement in the peak current density and redox reaction reversibility compared to a bare graphite felt. The modified graphite felt electrode enables 14- and 19-fold improvements in exchange current toward VO²⁺/VO₂⁺ and V³⁺/V²⁺ redox reactions, respectively, than those of a bare graphite felt. The battery performance at 50 mA cm^–2 of current density displays energy efficiency (89%) and electrolyte utilization (89%) nearly 12 and 98%, respectively, higher than that of a bare graphite felt. The long-term performance (200 cycles) of the battery assured stable behavior of the modified electrode. Moreover, the present modified approach improves the peak power density by 3-fold compared to that of the bare graphite felt.