Modulating single-atom sulfur-vacancy defect in MoS2-x catalysts to boost cathode redox kinetics for vanadium flow batteries

Vanadium flow batteries (VFBs) have great potential for application in energy storage systems. However, the sluggish cathode redox kinetics still greatly restricts their operation at high current densities. Herein, we boost cathode redox chemistry by modulating single-atom sulfur-vacancy (S-vacancy) defect of MoS2-x in-situ grown on carbon felts via a facile chemical etching method. Firstly, the optimized S-vacancy concentration is figured out via high throughput calculations based on d-band center theory. By precisely controlling etching duration, we achieve a tailored S-vacancy concentration, leading to highly dispersed S-vacancies, increased specific surface area, and improved hydrophilicity. Electrochemical characterizations demonstrate that optimized S-vacancy state can significantly facilitate the VO2+/VO2+ kinetics. Moreover, analysis of electron density difference and integrated crystal orbital Hamiltonian group further reveals that dispersed S-vacancy distribution also contribute to efficient surface electronic structure and enhanced adsorption process. Benefiting from enhanced VO2+/VO2+ kinetics, VFB single cell achieves a superior EE of 78.73% at 300 mA cm−2 and is able to last for 500 cycles without decay. This work demonstrates the promising potential of single-atom S-vacancies catalysts in the fabrication of flow battery electrodes and more importantly sheds light on the fundamental modulation essence of d-band center in MoS2-x towards enhanced cathode redox kinetics.