Formation of Ni _2.8 S ₂ -based heterojunctions with dual non-interfacial metal vacancies for enhanced hydrogen evolution performance

Vacancies in catalysts are known to critically influence catalytic activity, yet metal vacancies-especially non-interfacial metal vacancies-remain underexplored due to their intrinsically high formation energies and synthetic challenges. In this work, we successfully prepared a Ni_2.8S₂ precursor containing nickel vacancies through a high-temperature solid-state reaction, which was subsequently transformed <i>in situ</i> into a NiS/NiSe₂ heterostructure featuring dual non-interfacial metal vacancies. Notably, these vacancy characteristics were preserved during the phase transition, yielding a robust NiS/NiSe₂ heterointerface with enhanced charge transfer and strengthened interphase coupling. Compared with a vacancy-free NiS/NiSe₂ counterpart, the vacancy-enriched heterostructure exhibits markedly improved hydrogen evolution activity. Density functional theory (DFT) calculations further reveal that the dual non-interfacial vacancies induce a downward shift in the Ni d-band center, which plays a pivotal role in boosting catalytic performance. This study underscores the importance of non-interfacial metal vacancies in designing high-performance electrocatalysts for hydrogen evolution and offers valuable insights for developing efficient, low-cost, and non-precious metal-based catalysts.