(530g) Role of Transition-Metal Dopants in the Activation of MoSe2 for Hydrogen Evolution Reaction

Electrochemical water splitting (EWS) integrated with renewable sources of energy is a promising route for sustainable hydrogen production. However, in EWS, the hydrogen evolution reaction (HER) is currently best catalyzed by expensive platinum (Pt) metal catalyst and inexpensive HER catalysts are needed for a scalable and economical EWS. Molybdenum diselenide (MoSe₂)—a transition metal dichalcogenide—has emerged as a promising catalyst for HER but it shows lower catalytic activity than Pt, because of its poor electrical conductivity, high overpotential, and the limited number of active sites. Previous studies have shown that edges of MoSe₂ are highly active for HER, but the basal plane, which forms most of the catalyst surface is inert towards HER. For activation of the MoSe₂ basal plane, prior studies have focused on the introduction of highly active basal-plane Se vacancies or substitutional doping of metal atoms in MoSe₂. However, the interaction between dopants and Se vacancies—whether beneficial or detrimental towards HER—remaind to be fully understood. Here, we use density functional theory calculations to study the interactions between prototypical transition-metal (TM) dopants (Mn, Fe, Co, and Ni) and Se vacancies, and the consequent influence on hydrogen adsorption (a descriptor of HER activity in acidic media) at basal planes, edges, and Se vacancy sites. We explain trends in the free-energies of hydrogen adsorption and Se vacancy formation based on changes in the electronic structure of MoSe₂ upon TM doping, as well as due to structural changes arising upon the introduction of TM dopants. Broadly, our studies reveal that the studied electron-rich TM dopants favorably modify the electronic structure of MoSe₂ basal planes towards HER and, additionally, electrochemical generation of Se vacancies becomes more facile on doped basal plane and edges at smaller cathodic potentials. These newly formed Se vacancies are typically highly active towards HER and thus, substitutional doping can be viewed as a promising avenue for defect-mediated activation of MoSe₂.