Flexible and free-standing electrode for high-performance vanadium redox flow battery: Bamboo-like carbon fiber skeleton from textile fabric

Developing the free-standing and flexible electrodes with high current density and cycle stability is still under debate towards the extensive application of vanadium redox flow batteries (VRFBs). So far, carbon felts, carbon fibers and carbon papers are used which mostly prepared from fossil precursors make them unsustainable. Herein, we first sought to prepare a mechanically flexible and free-standing carbon cloth from terry cloth towel fabric (100% cotton) by using a simple pyrolysis method (TCC). Interestingly, we obtained a bamboo-like carbon fiber structure with a well-balanced micro, -meso, and -macro porosity. Moreover, a low-cost Polyethyleneimine (PEI) is used for Nitrogen doping on carbon cloth skeleton (N-TCC) to improve its electrochemical performance. The as-prepared N-TCC were utilized as efficient electrodes for the VRFBs with higher electrochemical activity towards vanadium species VO₂⁺/VO²⁺ than TCC and commercial graphite felt (GF) in a 3 electrode electrochemical cell i.e. half-cell. Interestingly, the VRFBs constructed with N-TCCs electrodes (both +ve and –ve half cells) in a full cell configuration at varied current densities from 40 to 160 mA cm⁻², we achieved an increased energy efficiency (EE), voltage efficiency (VE), and columbic efficiency (CE) compared to pristine CFs, and TCC based VRFBs. The newly designed cotton based electrodes establishes a unique opportunity for constructing a low-cost, metal-free VRFBs towards a large-scale commercialization of sustainable energy storage system.