Hierarchical oxygen rich-carbon nanorods: Efficient and durable electrode for all-vanadium redox flow batteries

We describe the fabrication of hierarchical oxygen and nitrogen enriched-carbon electrode materials from zein and polyacrylonitrile by a simple electrospinning technique for durable and high rate all-vanadium redox flow batteries (VRBs). The nitrogen-doped carbon nanorods (NCNR) provide abundant oxygen-rich and nitrogen active sites, and thereby, enhancing the catalytic activity toward both VO²⁺/VO₂⁺ and V²⁺/V³⁺ ion redox reactions by improving ion transfer kinetics and faster electron transfer rate in VRB. With improving electrocatalytic properties, the NCNR decorating carbon felt electrode (NCNR/CF) exhibits excellent battery performance with an impressive specific capacity of 37.3 Ah L⁻¹ than pristine CF (22.8 Ah L⁻¹) and CNR/CF (28.6 Ah L⁻¹) electrodes. The NCNR/CF electrode also shows an outstanding coulombic efficiency (CE, 98.9%) and energy efficiency (EE, 84.3%) compared with the pristine CF (CE, 91.2% and EE, 73.4%) and the CNR/CF (CE, 95.6% and EE, 81.2%) electrodes in the VRB at 40 mA cm⁻² current density. Furthermore, the NCNR/CF electrode exhibits 10.9 and 3.1% higher EE as compared to the pristine CF and CNR/CF electrodes, respectively. Therefore, the impressive cyclic rate capability with negligible capacity decay proves the superiority of NCNR as a potential electrode material for all-vanadium redox flow batteries.