N-Doping Coupled with Co-Vacancies Activating Sulfur Atoms and Narrowing Bandgap for CoS Toward Synergistically Accelerating Hydrogen Evolution.

The combination of hetero-elemental doping and vacancy engineering will be developed as one of the most efficient strategies to design excellent electrocatalysts for hydrogen evolution reaction (HER). Herein, a novel strategy for N-doping coupled with Co-vacancies is demonstrated to precisely activate inert S atoms adjacent to Co-vacancies and significantly improve charge transfer for CoS toward accelerating HER. In this strategy, N-doping favors the presence of Co-vacancies, due to greatly decreasing their formation energy. The as-developed strategy realizes the upshift of S 3p orbitals followed by more overlapping between S 3p y and H 1s orbitals, which results in the favorable hydrogen atom adsorption free energy change (ΔG H ) to activate inert S atoms as newborn catalytical sites. Besides, this strategy synergistically decreases the bandgap of CoS, thereby achieving satisfactory electrical conductivity and low charge-transfer resistance for the as-obtained electrocatalysts. With an excellent HER activity of -89.0 mV at 10.0 mA cm -2 in alkaline environments, this work provides a new approach to unlocking inert sites and significantly improving charge transfer toward cobalt-based materials for highly efficient HER.