Heterointerface-Vacancy Co-Engineering of VSe-NiSe2/CoSe2@C for Efficient Bifunctional Overall Water Splitting

Abstract

Simultaneously optimizing the disparate active sites for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a critical yet unmet challenge in bifunctional electrocatalyst design. Herein, we demonstrate a heterointerface-vacancy co-engineering strategy to construct VSe-NiSe2/CoSe2@C, in which a built-in electric field (BIEF) and abundant Se vacancies are synergistically integrated at the heterointerface. Operando Raman analysis combined with density functional theory (DFT) calculations confirms that the BIEF-vacancy synergy drives directional electron transfer from NiSe2 to CoSe2 through interfacial Ni-Se-Co bridging bonds, concurrently triggering surface self-reconstruction for enhanced OER and tailoring the adsorption energetics at Co sites (for HER) and Ni sites (for OER). Consequently, a two-electrode electrolyzer assembled with VSe-NiSe2/CoSe2@C achieves a current density of 10 mA cm-2 at a cell voltage of 1.62 V and maintains robust performance for more than 200 h. This study highlights heterointerface-vacancy co-engineering as a generalizable design principle for high-performance bifunctional transition metal selenide electrocatalysts.