Holey aligned electrodes through in-situ ZIF-8-assisted-etching for high-performance aqueous redox flow batteries

Fabricating electrodes with large specific surface area (SSA) and high permeability has been the long-standing target in redox flow batteries (RFBs). In this work, we propose a novel ZIF-8-assisted etching approach to form holey fibers in the electrospinning process of aligned electrode structures. The etching approach allows the formation of holey fibers with small pores of ~50 nm, offering large active surface areas for redox reactions, while the aligned macrostructure with the holey fibers of 3-5 μm in diameter ensures a high permeability along the fiber direction. The application of the prepared electrodes to a vanadium redox flow battery (VRFB) enables an energy efficiency (EE) of 87.2% at the current density of 200 mA cm^-2, which is 13.3% higher than that with conventional electrospun carbon electrodes. Even at high current densities of 300 and 400 mA cm^-2, the battery still maintains energy efficiencies of 83.3% and 79.3%. More excitingly, the prepared electrode yields a high limiting current density of 4500 mA cm^-2 and a peak power density of 1.6 W cm^-2. It is anticipated that the present electrospinning method combining the ZIF-8-assisted etching approach with a way to form ordered fiber structures will allow even more high-performance electrodes for RFBs in the future.