Comparative Studies on Nanocarbon-Modified Carbon Paper Electrodes for Enhanced Electrocatalytic Performance in Vanadium Redox Flow Batteries
Vanadium redox flow batteries (VRFBs) are a promising technology for large-scale energy storage due to their scalability, safety, long cycling life, and decoupled power and energy capacities. However, the slow redox kinetics of vanadium species on conventional carbon electrodes limits their performance. This study investigates the deposition of carbon black (CB), carbon nanotubes (CNTs), and electrochemically exfoliated graphene (Exf-Gr) onto thermally-activated carbon paper (ACP) via spray coating to enhance electrode electrocatalytic activity. Modified electrodes were characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and surface area analysis. Electrochemical properties were evaluated by cyclic voltammetry, electrochemical impedance spectroscopy, and single-cell VRFB testing. Among the modified electrodes, Exf-Gr/ACP exhibited 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 electrode performance in VRFB systems, with significant implications for large-scale energy storage.