In-situ functionalization of binder-free three-dimensional boron-doped mesoporous graphene electrocatalyst as a high-performance electrode material for all-vanadium redox flow batteries

Abstract The development of highly efficient and stable nanostructured electrocatalysts, capable of operating at a high current density is crucial to the broader market penetration of vanadium redox flow batteries (VRFBs). In this report, three-dimensional (3D) boron-doped mesoporous graphene functionalized carbon felt (BMG-CF) is fabricated and tested as the positive and negative electrodes for VRFB. Morphological results show that BMG-CF exhibits a homogenous distribution of boron atoms and the electrochemical testing indicates outstanding electrocatalytic activity towards VO2+/VO2+ and V2+/V3+ redox couples compared to activated-CF (A-CF) and mesoporous graphene-CF (MG-CF), ascribed to introduction of B-doped mesoporous structures and high electrical conductivity. Notably, BMG-CF attain energy efficiencies (EE) of 81.5% and 74.4% at 100 mA cm−2 and 150 mA cm−2, which are 9.4% (3.0%) and 17.3% (4.3%) higher than A-CF (MG-CF) electrodes. Furthermore, the battery can be operated at very high current densities of 175 mA cm−2 and 225 mA cm−2 with EE of 70.7% and 60.0% and exhibit excellent cycle stability for more than 100 cycles at 100 mA cm−2 with superior rate capability at current densities of 50–225 mA cm−2. The above excellent results demonstrate the practical applicability of the highly efficient and stable 3D BMG-CFs as promising electrodes for VRFB.