Three-dimensional mesoporous graphene-modified carbon felt for high-performance vanadium redox flow batteries

In our contribution, we study the synthesis of three-dimensional (3D) mesoporous graphene-modified carbon felt (MG-CF) via a facile self-assembly interaction method for the application of mesoporous graphene (MG) as an electrocatalyst for vanadium redox flow batteries (VRFBs). The MG loading on carbon felts (CFs) is systematically varied for optimal performance. Morphological and spectroscopic studies indicate that the MG exhibits a wrinkled configuration over the relatively smooth surface of the pristine CF (P-CF), and shows an increase in sp²/sp³ ratio. Nitrogen adsorption/desorption isotherms exhibit increase in specific surface area and porosity with increasing MG loading. Analysis of cyclic voltammetry and electrochemical impedance spectroscopy measurements reveal MG–CF–4 (4 wt% MG) possess the best electrochemical performance towards V²⁺/V³⁺ and VO²⁺/VO₂ ⁺ redox couples, attributing to optimal 3D MG strongly anchoring on the CF, enhancing conductivity, specific surface area, and electrochemical activity. In addition, charge/discharge measurements exhibit a high energy efficiency (EE) of 76.5% at 100 mA cm⁻² in MG–CF–4, compared to P-CF (66.2). Moreover, a higher energy efficiency (61.6%) and voltage efficiency (62.6) is obtained at a high current density of 175 mA cm⁻² with MG–CF–4 electrode. Furthermore, MG–CF–4 shows excellent stability and rate capability (EE of 74.9% and VE of 77.5 after 100 charge/discharge cycles at 100 mA cm⁻²), demonstrating superior performance of the modified electrodes during the vanadium ions redox reaction under acidic conditions.