Standalone macroporous graphitic nanowebs for vanadium redox flow batteries

Vanadium redox flow batteries (VRFBs) have attracted much attention as next-generation large-scale energy storage devices. However, they suffer from a drop in the energy efficiency induced by the large activation polarization during vanadium redox reactions. In this study, we designed electrode materials with a high energy efficiency that are a macroporous monolith composed of three-dimensionally entangled graphitic nanoribbons. These materials were denoted as macroporous graphitic nanowebs (M-GNWs), possessing a high specific surface area of 213 m ² g ⁻¹ and a large pore volume of 0.82 cm ³ g ⁻¹ . A large number of oxygen functional groups (C/O ratio of 4.4) were introduced after immersing the M-GNWs in the acidic electrolyte used in VRFBs. These properties of M-GNWs led to beneficial electrochemical catalytic effects such as low anodic and cathodic peak potential separation (△E _p ) values of ∼73.4 mV (catholyte) in a cyclic voltammetry test conducted at a sweep rate of 2 mV s ⁻¹ . Furthermore, the VRFBs based on an M-GNW anode and cathode pair exhibited a significantly improved energy efficiency of 85.8%, which is 12.4% higher than that (73.4%) of the commercial carbon felt-based VRFBs.