Engineering Cu1.96S/Co9S8 with sulfur vacancy and heterostructure as an efficient bifunctional electrocatalyst for water splitting

Defect and interface engineering have been recognized as efficient strategies for developing high-performance electrocatalysts. However, it is still challenging to couple defect and interface engineering in transition metal sulfides and understand their dynamic evolution process during electrocatalysis. Herein, we developed one-step pyrolysis of bimetallic sulfide to construct S vacancy-rich Cu1.96S/Co9S8 heterostructure by controlling the critical decomposition temperature. The as-synthesized Cu1.96S/Co9S8 exhibits excellent bifunctional electrocatalytic performance, with a low overpotential of 99 and 200 mV at 10 mA cm−2 towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1.0 mol/L KOH electrolyte, respectively. A symmetric two-electrode cell with Cu1.96S/Co9S8 delivered a current density of 10 mA cm−2 at a low voltage of 1.43 V and showed long-term stability for 200 h. A series of in/ex-situ techniques revealed that the electrochemical reconfiguration only appeared in the OER process, resulting in the CoOOH/CuO and SO42− species promoting OER performance. Meanwhile, the S vacancy and heterostructure interface in Cu1.96S/Co9S8 were proved to optimize the electronic structure and the adsorption of intermediates for HER by density function theory (DFT) simulations. This work provides a promising strategy to construct metal sulfides with rich defects and heterogeneous interfaces and understand their dynamic evolution process for electrochemical storage and conversion devices.