Hydrogen adsorption on MoS2-surfaces: a DFT study on preferential sites and the effect of sulfur and hydrogen coverage

We report a comprehensive computational study of the intricate structure-property relationships governing the hydrogen adsorption trends on MoS2 edges with varying S- and H-coverages, as well as provide insights into the role of individual adsorption sites. Additionally, the effect of single- and dual S-vacancies in the basal plane on the adsorption energetics is assessed, likewise with an emphasis on the H-coverage dependency. The employed edge/site-selective approach reveals significant variations in the adsorption free energies, ranging between similar to +/- 1.0 eV for the different edges-types and S-saturations, including differences of even as much as similar to 1.2 eV between sites on the same edge. The incrementally increasing hydrogen coverage is seen to mainly weaken the adsorption, but intriguingly for certain configurations a stabilizing effect is also observed. The strengthened binding is seen to be coupled with significant surface restructuring, most notably the splitting of terminal S-2-dimers. Our work links the energetics of hydrogen adsorption on 2H-MoS2 to both static and dynamic geometrical features and quantifies the observed trends as a function of H-coverage, thus illustrating the complex structure/activity relationships of the MoS2 catalyst. The results of this systematical study aims to serve as guidance for experimentalists by suggesting feasible edge/S-coverage combinations, the synthesis of which would potentially yield the most optimally performing HER-catalysts.