Anion substitution induced vacancy regulating of cobalt sulfoselenide toward electrocatalytic overall water splitting

Abstract

Anion substitution is a valid strategy to modulate the active sites of the transition metal dichalcogenides (TMDs). Herein, a series of cobalt sulfoselenide nanomeshes (CoS2(1-x)Se2x@NC) were synthesized by calcining S/Se power with ultrathin metal–organic framework (MOFs) nanosheets. The vacancy concentration of CoS2(1-x)Se2x@NC could be adjusted through changing the ratio of S/Se precursor. Interestingly, CoS1.25Se0.75@NC electrocatalyst possesses the largest vacancy concentration as well as the optimal electrocatalytic performance. CoS1.25Se0.75@NC delivers an overpotential as low as 134 mV for hydrogen evolution reaction (HER) and 270 mV for oxygen evolution reaction (OER) at the current density of 10 mA cm -2, respectively. Furthermore, CoS1.25Se0.75@NC affords a low cell voltage of 1.67 V (at 10 mA cm−2) and outstanding cycling stability for overall water splitting reaction (more than 55 h). For HER process, theoretical calculations prove that anion vacancy not only lower the free energy barrier of H2O dissociation step but also favor the desorption step of intermediate H*. For OER process, the anion vacancies could modulate the adsorption/desorption free energy of oxygen-containing intermediates. The present work demonstrates a practical approach to modulate the vacancy concentration of cobalt sulfoselenide and provides new ideas for design of efficient non-metal electrocatalysts.