In Situ Tracking of Se Vacancy-Promoted Surface Reconstruction of NiCoSe2 into NiCoOOH during Alkaline Oxygen Evolution

Abstract

Understanding the dynamic surface reconstruction of precatalyst materials during the oxygen evolution reaction (OER) is a forefront area of research for designing and studying effective electrocatalysts. Here, we report the deliberate engineering of Se vacancies in NiCoSe2 via a facile NaBH4 reduction strategy and systematically investigate how anion vacancies govern surface reconstruction behavior under alkaline OER conditions. The presence of Se vacancies is confirmed via EPR spectroscopy and ICP-MS analysis. Cyclic voltammetry and in situ electrochemical impedance spectroscopy during the electrochemical activation process reveal that the vacancy-enriched NiCoSe2–x undergoes faster and more extensive structural reconstruction than pristine NiCoSe2. Quasi in situ ATR-FTIR and Raman spectroscopy track the dynamic evolution of NiCoOOH during anodic polarization, providing direct spectroscopic evidence for the Se vacancy-promoted NiCoOOH active phase generation with abundant Ni–O–Co synergy. Evaluation of electrochemical surface area and turnover frequency establishes that the generation of abundant Ni–O–Co synergy in NiCoSe2–x simultaneously increases the density of accessible active sites and enhances the intrinsic activity per site. Consequently, the NiCoSe2–x precatalyst delivers significantly improved OER performance relative to bare NiCoSe2, along with high Faradaic selectivity and long-term stability. Post-stability characterizations confirm bulk structural and morphological reconstruction driven by Se vacancies and thus highlight the complete utilization of the available catalytic sites. This work provides a fundamental mechanistic framework linking anion vacancy engineering, surface reconstruction kinetics/mechanism tracking, and intrinsic OER activity enhancement in bimetallic chalcogenide precatalysts, offering rationalized design principles for next-generation earth-abundant OER catalysts.