Role of the Edge Properties in the Hydrogen Evolution Reaction on MoS₂

Abstract

Molybdenum disulfide, in particular its edges, has attracted considerable attention as possible substitute for platinum catalysts in the hydrogen evolution reaction (HER). The complex nature of the reaction complicates its detailed experimental investigations, which are mostly indirect and sample dependent. Therefore, density functional theory calculations were employed to study how the properties of the MoS Mo-edge influence the thermodynamics of hydrogen adsorption onto the edge. The effect of the computational model (one-dimensional nanostripe), border symmetry imposed by its length, sulfur saturation of the edge, and dimensionality of the material are discussed. Hydrogen adsorption was found to depend critically on the coverage of extra sulfur at the Mo edge. The bare Mo-edge and fully sulfur-covered Mo-edge are catalytically inactive. The most favorable hydrogen binding towards HER was found for the Mo-edge covered by sulfur monomers. This edge provides hydrogen adsorption free energies positioned around -0.25 eV at up to 50 % hydrogen coverage, close to the experimental values of overpotential needed for the HER reaction.

Is Single Layer MoS2 Stable in the Air?

“…In the SO 2 configuration, both O atoms adsorb above the same sulfur atom (Figure ). Their adsorption induces a two‐fold periodic reconstruction of the edge, similarly to the adsorption of hydrogen during the hydrogen evolution reaction . The formation of the SO 2 group elongates the Mo−S bonds of the participating S atom, displacing it by 1.09 Å relative to its initial position.…”

“…Their adsorption induces at wo-fold periodic reconstruction of the edge, similarly to the adsorption of hydrogen during the hydrogen evolution reaction. [27] The formation of the SO 2 group elongates the MoÀSb onds of the participating Sa tom, displacing it by 1.09 relative to its initial position. The SÀOb ond length of the SO 2 group is 1.45 and its dihedral angle is 119.68,b oth of which are consistent with the corresponding values in isolated SO 2 molecules.…”

Metal Boride‐Based Catalysts for Electrochemical Water‐Splitting: A Review

“…For instance, the supremely high HER performance of Pt is majorly ascribed to its optimum H‐bonding strength as it sits at the top of the Volcano plot ( Figure a) . Similarly, electrocatalysts belonging to the sulfide (MoS 2 ) family show HER activity owing to the highly active sulfur atoms on the Mo edges of MoS 2 planes (Figure b) . In case of phosphides (Ni, Co, and Mo based), higher HER activity is attributed to the “ensemble effect” (also called “ligand effect”) where the positively charged metal center (M δ + ) acts as the hydride acceptor while the negatively charged phosphorous center (P δ − ) acts as the proton acceptor, facilitating HER.…”

“…b) A model representation of the MoS 2 nanostripe with exposed Mo‐edge on its right side covered by sulfur monomers. Adapted with permission . Copyright 2017, Wiley‐VCH.…”

Stability, Structure and Reconstruction of 1H‐Edges in MoS2

“…Mo‐50 %S edges form by S atoms bridging neighboring Mo atoms. Previous studies show that periodic lattice distortions occur along these edges . In the current study, we explore different possible distortions on this edge and determine the most favorable.…”