Construction of heterogeneous core–shell CoFeMo polymetallic sulfide/N-rich carbon skeleton composite catalysts based on stepwise displacement of MOF for overall water splitting

The low electron transfer efficiency compared to precious metals, few active sites and poor stability of transition metal sulfides (TMSs) limit their wide application in electrocatalysis. Optimizing the electronic structure and morphology is an effective means to improve the catalytic performance of TMSs. In this work, we synthesized a heterogeneous core–shell CoFeMo polymetallic sulfide/N-rich carbon skeleton composite catalyst (CFMS/NC) with CoMo-S as the core and CoFeMo-S as the shell by using MOF as precursor and stepwise substitution method. Compared with monomeric sulfides, polymetallic sulfides can exert the synergistic effect between metals, optimize the electronic structure and improve the intrinsic activity of metallic sulfides. Meanwhile, the core–shell structure supported by N-rich carbon skeleton has larger active specific surface area, higher stability and conductivity. The overpotential of CFMS/NC catalyst is only 122 mV at 10 mA cm−2 for hydrogen evolution reaction (HER) and 325 mV at 50 mA cm−2 for oxygen evolution reaction (OER). Besides, CFMS/NC exhibits outstanding performance in overall water splitting, achieving a current density of 100 mA cm−2 at only 1.76 V and maintaining good stability for 30 h. This study proposes a practical method for synthesizing highly efficient electrocatalysts for water splitting.