Comparative studies on nanocarbon-modified carbon paper electrodes for enhanced electrocatalytic performance in vanadium redox flow batteries

Vanadium redox flow batteries (VRFBs) are a means of large-scale energy storage due to their excellent scalability, safety, long cycling life, and decoupled power and energy capacities. However, the slow redox kinetics of vanadium species on conventional carbon electrodes remains a major limitation to their performance. We investigated the deposition of carbon black, carbon nanotubes, and electrochemically exfoliated graphene (Exf-Gr) onto thermally-activated carbon paper (ACP) by spray coating to increase the electrode electrocatalytic activity. The modified electrodes were characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X -ray photoelectron microscopy, and surface area analysis, while their electrochemical properties were evaluated by cyclic voltammetry, electrochemical impedance spectroscopy, and single-cell VRFB testing. Among the modified electrodes, Exf-Gr/ACP had the best performance, achieving a 2.9-fold reduction in charge transfer resistance compared to pristine ACP and delivering 2.5 times the discharge capacity in single-cell tests. This improvement is attributed to Exf-Gr’s high surface area, favorable catalytic activity, and excellent dispersion on the ACP substrate. Surface modification with electrochemically exfoliated graphene is a highly effective strategy for improving the electrode performance in VRFB systems, with significant implications for large-scale energy storage.