A novel electrode formed with electrospun nano- and micro-scale carbon fibers for aqueous redox flow batteries

This work reports on a novel electrode prepared with electrospun nano- and micro-scale carbon fibers for aqueous redox flow batteries. Larger fibers, ~10 μm in diameter, form larger pores to provide pathways for electrolyte flow, while smaller fibers, ~1 μm in diameter, increase active surface area for redox reactions. Brunauer-Emmett-Teller and pressure drop tests show that the specific surface area of the prepared dual-diameter electrode is doubled as compared with the large-fiber electrode, while the estimated permeability is enhanced by 1.4 times as opposed to the small-fiber electrode. The application of the dual-diameter electrodes to a vanadium redox flow battery allows the battery to achieve an energy efficiency of 84.78% at the current density of 100 mA cm⁻², which is 13.57% higher than that with small-fiber electrodes, and 3.91% higher than that with large-fiber electrodes. Even at a high current density of 200 mA cm⁻², the battery with the prepared electrode can still maintain the energy efficiency of 74.18%, which is 5.5% higher than that with large-fiber electrodes, and the battery with small-fiber electrodes cannot be operated at such high current density. This dual-diameter fibrous structure provides inspirations for the future electrode design in aqueous redox flow batteries.