Structure of Nanocrystalline, Partially Disordered MoS2+δ Derived from HRTEM—An Abundant Material for Efficient HER Catalysis

Abstract

Molybdenum sulfides (MoSx, x > 2) are promising catalysts for the hydrogen evolution reaction (HER) that show high hydrogen evolution rates and potentially represent an abundant alternative to platinum. However, a complete understanding of the structure of the most active variants is still lacking. Nanocrystalline MoS2+δ was prepared by a solvothermal method and immobilized on graphene. The obtained electrodes exhibit stable HER current densities of 3 mA cm−2 at an overpotential of ~200 mV for at least 7 h. A structural analysis of the material by high-resolution transmission electron microscopy (HRTEM) show partially disordered nanocrystals of a size between 5–10 nm. Both X-ray and electron diffraction reveal large fluctuations in lattice spacing, where the average c-axis stacking is increased and the in-plane lattice parameter is locally reduced in comparison to the layered structure of crystalline MoS2. A three-dimensional structural model of MoS2+δ could be derived from the experiments, in which [Mo2S12]2− and [Mo3S13]2− clusters as well as disclinations represent the typical defects in the ideal MoS2 structure. It is suggested that the partially disordered nanostructure leads to a high density of coordinatively modified Mo sites with lower Mo–Mo distances representing the active sites for HER catalysis, and, that these structural features are more important than the S:Mo ratio for the activity.

Influence of Oxygen Dopants on the HER Catalytic Activity of Electrodeposited MoOxSy Electrocatalysts

“…To avoid any crystallization, the samples were annealed at 250 °C. The difference in the Raman spectra highlights that the electrodeposited amorphous films show structures fundamentally different from that of crystalline MoS 2 . ,, This is also evident in the XRD where the crystallized sample exhibits a strong diffraction of the Mo (002) plane, whereas the samples annealed at 250 °C only show a slight hump, likely due to short-range ordering. , The non-annealed samples do not exhibit any hump, and no samples exhibited features other than that of MoS 2 or the substrates (Figure S3). Additionally, when left in air, the features associated with MoO vibrations increase in intensity, demonstrating that the film oxidizes over time. , Both annealed samples closely resemble the as deposited spectra; however, there are small differences around 450 and 530 cm –1 .…”

“…6,30,41 This is also evident in the XRD where the crystallized sample exhibits a strong diffraction of the Mo (002) plane, whereas the samples annealed at 250 °C only show a slight hump, likely due to short-range ordering. 42,43 The non-annealed samples do not exhibit any hump, and no samples exhibited features other than that of MoS 2 or the substrates (Figure S3). Additionally, when left in air, the features associated with MoO vibrations increase in intensity, demonstrating that the film oxidizes over time.…”

Surface Anchoring and Active Sites of [Mo3S13]2– Clusters as Co-Catalysts for Photocatalytic Hydrogen Evolution

“…The restructuring to chain-like structures shows the tendency of the clusters to organize in a highly disordered MoS 2 -like motif similar to that described recently. 37 2.2.3. Adsorption Model.…”

Mo2C-MoS2 heterojunction a suitable and stable electrocatalyst for HER and supercapacitor Applications

“…Hydrogen is regarded as the best alternative, highly efficient, and zero toxic exhaustion fuel. Hydrogen is usually produced from the water via electrochemical, photocatalytic, and photoelectrochemical water splitting through hydrogen evolution reaction (HER) [1][2][3][4][5]. Hydrogen production through the above procedures necessarily requires active and stable catalyst species for commercial-scale use [6,7].…”

“…These energy In present scenario, molybdenum (Mo) based compounds such as nitrides, carbides, and sulfides have displayed Pt-like catalytic properties in addition to their higher stability and mechanical strength. [5,[10][11][12][13][14][15][16][17]. Among these, molybdenum disulfide (MoS2), when exfoliated to mono or few layers structures has exhibited high activity for HER, but the occurrence of active sites at only edges have caused major limitations [18,19].…”