A highly-stable bifunctional NiCo2S4 nanoarray@carbon paper electrode for aqueous polysulfide/iodide redox flow battery

Abstract

Aqueous polysulfide/iodide redox flow battery (SIFB) has the advantages of the high solubility of active materials, flexible designability, and low cost, which shows great potential in the field of grid-scale energy storage. However, the poor electrochemical activity of polysulfide limits the energy density and power density of the battery, which hinders its further commercial application. Herein, self-supported NiCo2S4 nanoneedle arrays are successfully synthesized on carbon paper (CP) through a two-step hydrothermal method. The as-prepared materials not only possess unique adsorption and electrocatalytic properties for polysulfide, but also promote the electrocatalytic process of iodide, which realizes bifunctional catalysis. The polysulfide/iodide redox flow battery with NiCo2S4@CP electrode can achieve a peak power density of 82.4 mW cm−2 at 160 mA cm−2 which is much higher than that with the pure CP electrode (∼12 mW cm−2). It can operate stably for more than 3400 h at a current density of 10 mA cm−2 with a capacity fade decay rate of 0.218% per day, exhibiting ultra-long cycle stability.