Electrospun carbon nanofiber inlaid with tungsten carbide nanoparticle by in-situ carbothermal reaction as bifunctional electrode for vanadium redox flow battery

Abstract This work provided a novel tungsten carbide (WC) nanoparticle catalyst which was uniformly inlaid in carbon nanofiber (CNF) without help of binder by in-situ carbothermal reaction and electrospinning technology to obtain CNF/WC composite for use as bifunctional electrode for vanadium redox flow battery (VRFB). Ammonium tungstate was used as tungstate source to obtain CNF/WC composites consisting of different amounts of WC (CNF/WC-05, CNF/WC-10, and CNF/WC-20). Ammonium tungstate was decomposed to tungsten trioxide at high temperature, which was subsequently converted to WC by way of an in-situ carbothermal reaction with increasing temperature. The electrochemical performance of CNF/WC composite is improved due to that WC nanoparticle can increase active sites towards vanadium redox reaction. CNF/WC-10 presents the best electrochemical performance for V3+/V2+ redox reaction as well as an increase in electrochemical performance for VO2+/VO2+ redox reaction compared with CNF. The cell using CNF/WC-10 as bifunctional electrode exhibits an increase in energy storage performance including higher energy efficiency and discharge capacity. In comparison with pristine cell, the cell using CNF/WC-10 shows better stability in 50-cycle charge-discharge operation at 50 mA cm−2. Especially, the cell using CNF/WC-10 presents an increase in energy and voltage efficiency compared with pristine cell at high current density, suggesting that CNF/WC-10 electrode decreases electrochemical polarization of cell. At 150 mA cm−2, the cell using CNF/WC-10 presents an increase of 7.2% in energy efficiency compared with pristine cell (61.1%). Overall, the results demonstrate excellent electrochemical performance of WC for vanadium redox reaction and provide guidelines for exploring carbide catalyst in future VRFB study.