Boosting alkaline hydrogen evolution reaction via an unexpected dynamic evolution of molybdenum and selenium on MoSe${}_2$ electrode

Transition metal chalcogenides are a promising and extremely pivotal class of electrocatalysts with potential applications in alkaline hydrogen evolution reaction (HER), especially, molybdenum diselenide. Although the exposed edge sites are generally considered to be the active sites of MoSe${}_2$ for HER, an intrinsic behavior (surface species evolution, structure/morphology conversion, stability) of MoSe${}_2$ electrode itself was not unveiled. Herein, the origin of MoSe${}_2$-electrocatalyzed HER activity monitored by the quasi-operando XPS and in situ Raman spectroscopy is presented. The findings clearly show dynamic evolution of both Mo and Se species on MoSe${}_2$ electrode surface for promoting HER activity and maintaining long-term catalytic stability and reveal an electro-oxidative dissolution and re-adsorption mechanism. Theoretical calculations also corroborate these results. As expected, the addition of single or mixed MoO${}_4$${}^{2-}$ and SeO${}_3$${}^{2-}$ to the electrolyte of nickel foam directly verifies the critical role of surface-adsorbed Mo and Se species for boosting HER activity and stability. Additionally, the oxidative dissolution of Se on Ni${}_x$Se${}_y$ electrode surface during HER is also observed, revealing the universality of oxidative dissolution of Se in transition metal selenides. This study provides a unique insight into the species evolution and surface structure transformation mechanism and activity improved origin of materials during the electroreduction process. (© 2022 The Authors. Advanced Energy Materials published by Wiley‐VCH GmbH)