Comprehensive Phase Diagrams of MoS₂ Edge Sites Using Dispersion-Corrected DFT Free Energy Calculations

A comprehensive set of surface phase diagrams addressing the catalytically relevant edges of the (100) surface of MoS₂ catalysts is developed using dispersion-corrected density functional theory and ab initio thermodynamic modeling. The results of the temperature-dependent, free energy-based thermodynamic model are presented over the full range of catalytically relevant temperatures and pressures, in addition to S- and H-coverages ranging from 0 to 100%. The results of this work allow for a full thermodynamic analysis to be performed at the conditions relevant to any promising reaction involving MoS₂, ranging from hydrodesulfurization to dehydrogenation to electrocatalysis. Several methodological recommendations are discussed and implemented with the goal of improving the accuracy of the surface phase diagrams at minimal computational expense. A library of the most stable S- and H-adsorption modes is also developed so that linear scaling relationships can be used to correlate thermodynamic stability with kinetic activity. Applying the results to C-H bond activation of methane with a S₂ oxidant, we predict S-coverages near 100% on the Mo- and S-edges to be thermodynamically favored and S monomers on edge sites with high S-coverages to be kinetically favorable. For H-abstraction on surface S atoms, the Mo-edge is also predicted to be more active than the S-edge.