Single-Atom Metal Tuned Sulfur Vacancy for Efficient H2 Activation and Hydrogen Evolution Reaction on Mos2 Basal Plane

Abstract

MoS2(001) basal plane, modified by doping transition metals (M) or creating S vacancies (Sv), has presented superior catalytic performance in hydrogen evolution, hydrogenation and hydrodeoxygenation reactions. However, the optimal active sites for H2 dissociation/recombination, a crucial step in the aforementioned reactions, on the modified MoS2(001) are yet to be unequivocally elucidated. Using density functional theory calculations, we find that H2 dissociation activity generally follows the order: M modified Sv>unmodified Sv>M modified S>M modified Sv ̶ M and Sv modified S>M and Sv modified S>Sv modified S>unmodified S. Compared to Mo, the increasing number of outer electrons in M leads to less unpaired electrons to bind with S. This greatly facilitates the removal of S (Sv formation), which leaves electrons to fill to the antibonding σu H2 states, thereby enhancing H2 dissociation through homolytic mechanism. M modified Sv also exhibits superior activity in H2 recombination and hydrogen evolution, indicating it to be the active site for these reactions. The energetic proportionality between Sv formation energy, integrated crystal orbital overlap/Hamilton populations and H adsorption energy together with BEP relations open the possibilities for optimal design of MoS2 and other metal compound catalysts for important reactions of technological interest, where hydrogen is involved.

Keywords: MoS2, single-atom doping, S vacancy, H2 activation, hydrogen evolution, DFT calculations