Activated Charcoal Modified Graphite Felts Using for Positive Electrodes of Vanadium Redox Flow Battery

In the present paper, a composite electrode material was developed for vanadium redox flow batteries (VRFBs). Activated charcoal particles were evenly immobilized on the graphite felt (GF) via a sucrose pyrolysis process for the first time. The in site formed pyrolytic carbon is used as the binder, because it is essentially carbon material as well as GF and activated charcoal, which has a natural tendency to realize good adhesion and low contact resistance. The activated charcoal decorated GF electrode (abbreviated as the composite electrode) possesses larger surface area (13.8 m² g⁻¹), more than two times as GF (6.3 m² g⁻¹). The oxygen content of composite electrode is also higher (7.0%) than that of GF (4.8%). The composite electrode was demonstrated to lower polarization and increase the reversibility toward the VO²⁺/VO₂⁺ redox couple according to the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The charge–discharge cycling test was conducted with a single VRFB cell. The results indicate that the cell with composite electrode presents higher charge–discharge capacity, larger electrolyte utilization efficiency (EU), and higher energy conversion efficiency (79.1%) compared with that using GF electrode. The increasing electrochemical performances of composite electrodes are mainly ascribed to the high electrochemical activity of activated charcoal particles and increasing superficial area.