Mapping Catalytically Relevant Edge Electronic States of MoS₂

Abstract

Molybdenum disulfide (MoS2) is a semiconducting transition metal dichalcogenide that is known to be a catalyst for both the hydrogen evolution reaction (HER) as well as for hydro-desulfurization (HDS) of sulfur-rich hydrocarbon fuels. Specifically, the edges of MoS2 nanostructures are known to be far more catalytically active as compared to unmodified basal planes. However, in the absence of the precise details of the geometric and electronic structure of the active catalytic sites, a rational means of modulating edge reactivity remain to be developed. Here we demonstrate using first-principles calculations, X-ray absorption spectroscopy, as well as scanning transmission X-ray microscopy (STXM) imaging that edge corrugations yield distinctive spectroscopic signatures corresponding to increased localization of hybrid Mo 4d states. Independent spectroscopic signatures of such edge states are identified at both the S L2,3 and S K-edges with distinctive spatial localization of such states observed in S L2,3-edge STXM imaging. The presence of such low-energy hybrid states at the edge of the conduction band is seen to correlate with substantially enhanced electrocatalytic activity in terms of a lower Tafel slope and higher exchange current density. These results elucidate the nature of the edge electronic structure and provide a clear framework for its rational manipulation to enhance catalytic activity.

Direct synthesis of metastable phases of 2D transition metal dichalcogenides

“…17 These one-dimensional states were first predicted by M. Bollinger et al 219 and later visualised using scanning tunnelling microscopy 219 and scanning transmission X-ray microscopy. 220 The thermochemistry predictions were verified by T. Jaramillo et al by measuring the catalytic activity of UHV sputtered MoS 2 nanoislands of various sizes. 17 The observed correlation between the rate of hydrogen evolution and the fraction of edge sites of MoS 2 nanoparticles unambiguously suggests that in the case of semiconducting 2H MoS 2 nanostructures, the electrocatalytic HER predominantly takes place at the edge sites.…”

Identifying Catalytic Active Sites of Trimolybdenum Phosphide (Mo3P) for Electrochemical Hydrogen Evolution

“…Developing nonprecious metal catalysts with increased activity and durability is crucial to advance solid‐state electrocatalysis for sustainable energy technologies that mainly rely on precious metals such as platinum (Pt), palladium (Pd), and silver (Ag) . Recently, 2D nanomaterials such as molybdenum disulfide (MoS 2 ) and carbide (Mo 2 C) have been identified as promising candidates to replace precious metal catalysts owing to the unique electronic properties of their edge structures . However, the basal plane of these catalysts containing substantial amount of their surface structure remains nearly inactive making these catalysts inefficient, especially for practical applications .…”

Tunable Electronic Properties of Lateral Monolayer Transition Metal Dichalcogenide Superlattice Nanoribbons

“…Clearly, the H passivation of the zigzag (MoS2)3/ (WS2)3 nanoribbon does not make the system semiconducting. Both the symmetric and asymmetric armchair nanoribbons may lower their energy via formation of corrugation [33] or the bond reconstruction mechanism, as is widely realized for semiconductor surfaces, particularly the (001) surface of diamond structure materials and the (110) surface of zincblende materials [54]. However, in this work we have not considered any possible reconstructions of geometries discussed in the text.…”

“…Previous research shows MoS 2 , WS 2 , MoSe 2 , WSe 2 zigzag nanoribbons as metallic and ferromagnetic and the armchair nanoribbons as semiconducting [ 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. The edges of MoS 2 nanostructures are known to be very catalytically active [ 33 ]. Parija et al demonstrated that edge corrugations yield distinctive spectroscopic signatures using first-principles calculations, X-ray absorption spectroscopy, scanning transmission X-ray microscopy (STXM) imaging [ 33 ].…”

“…The edges of MoS 2 nanostructures are known to be very catalytically active [ 33 ]. Parija et al demonstrated that edge corrugations yield distinctive spectroscopic signatures using first-principles calculations, X-ray absorption spectroscopy, scanning transmission X-ray microscopy (STXM) imaging [ 33 ]. The electronic properties of armchair MoS 2 nanoribbon can be adjusted by passivating atoms on the edge and by changing the width, which is expected to make them useful for semiconductor functional electronic devices [ 24 , 32 , 34 , 35 , 36 ].…”