Defect-rich graphene skin modified carbon felt as a highly enhanced electrode for vanadium redox flow batteries

Vanadium redox flow batteries (VRFBs) with high energy density, long cycle life, flexible design and rapid response have attracted great attention in large-scale energy storage applications. However, the low activity of traditional carbon felt electrodes severely limits its practical implementation. Herein, we report the fabrication of modified carbon felt (CF) by coating defect-rich graphene through chemical vapor deposition (CVD) and subsequent Ar plasma treatment as a highly improved electrode (denoted as Ar-GCF) for VRFB. The modification of defect-rich graphene skin can not only expose a large number of graphene edges as highly active sites, but also offers copious oxygen-containing functional groups to improve the electronic conductivity of Ar-GCF and accelerate the VO2+/VO2+ redox, which are demonstrated by both electrochemical measurements and spin-polarized density functional theory (DFT) calculations. As a result, the VRFB with Ar-GCF electrode exhibited an improved energy efficiency (EE) by 7.10% compared with that of VRFB using an unmodified CF electrode. Moreover, the Ar-GCF electrode showed excellent stability, with the charge transfer resistance (Rct) increased by merely 15.79% after 800 cycles, while the Rct of CF electrode increased by 102.40% after 600 cycles.