Constructing molybdenum vacancy defect for MoP with optimized p-band center towards high-efficiency hydrogen evolution

Vacancy engineering has been widely used to enhance the hydrogen evolution reaction (HER) performance due to its effective electronic modulation effect. Herein, the molybdenum (Mo) vacancies were introduced into molybdenum phosphide (MoP) towards high-efficiency hydrogen evolution for the first time. Benefiting from the charge redistribution around the Mo vacancies, the exposed P sites can serve as ideal catalytic sites with a free energy of hydrogen adsorption close to zero. Meanwhile, an internal polarization field from terminal Mo atoms to exposed P atoms can offer a more efficient "H delivery" mechanism, achieving fast HER kinetics with a dominant Volmer-Heyrovsky mechanism at a wide range of current density and ultimately exceeding the commercial Pt/C catalyst for high-efficiency hydrogen evolution. More importantly, we first report that the P p-band center can be used as an alternative descriptor to evaluate the HER performance of the electrocatalysts which utilize P atoms as the main active sites. Furthermore, this work also demonstrates that metal vacancies provide an effective tactic to optimize catalytic activity for metal compound-based electrocatalysts.