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

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.