Tailoring of 1T Phase-Domain MoS₂ Active Sites with Bridging S₂^2–/Apical S^2– Phase-Selective Precursor Modulation for Enriched HER Kinetics

Abstract

Molybdenum disulfide (MoS2) is a promising alternative electrocatalyst for hydrogen evolution reaction (HER) due to its relatively near zero hydrogen adsorption free energy (ΔG H = 0.08) and availability as a metallic (1T) phase. The superior catalytic activity of the 1T phase over 2H is owing to the availability of dense active sites, 107 fold higher conductivity, and greater hydrophilicity. However, in the synthesis of 1T-MoS2, a highly controlled proficient method is indispensable due to its metastable nature. Besides, phase enrichment is greatly sensitive to experimental parameters such as precursor, temperature, reaction time, and solvent. In the context of precursors, to date, no single precursor has been recognized as a selective precursor for the synthesis of 1T-MoS2. In this work, MoS2 with high content of 1T phase (79.4%) and excessive bridging S2 2–/apical S2– sites has been formulated from a single precursor, that is, ammonium tetrathiomolybdate ((NH4)2MoS4), ATTM). In HER, it displayed an inspired activity, that is, achieving 10 mA cm–2 current density, it requires just 248 mV overpotential with a minimal Tafel slope value (56 mV/dec). The maximum enrichment of the 1T phase, abundant accumulation of catalytically active bridging S2 2–/apical S2– sites, and the complete reduction of Mo+6 to Mo+4 (absence of Mo+6) are root causes for the outstanding activity of the synthesized 1T phase-domain MoS2. To the best of our knowledge for the very first time, here, we declare that the single source, that is, ATTM is an exclusive precursor for the selective synthesis of 1T-MoS2 with advantageous structural features. Moreover, this expedient precursor could be more pertinent for the industrial-scale preparation of 1T phase-domain MoS2 in near future.

Modulating Crystallization of MoS2 Nanostructures by Dimethyl Sulfoxide for Enhanced Hydrodesulfurization

“…The sharp signal peak observed before 200 °C is attributed to the reduction of the (S–S) 2 – structure, which is believed to be the catalytic site of HDS reaction . Unlike the standard arrangement of S 2 – in MoS 2 crystals and edges, these (S–S) 2 – units are bridged between two Mo atoms at the edge of MoS 2 . , The abundant (S–S) 2– structures in MoS 2 -C and MoS 2 -C-3 are consistent with the XPS results. However, unlike MoS 2 -C, MoS 2 -C-3 exhibited a significantly higher hydrogen consumption between 200 and 600 °C.…”

“…33 Unlike the standard arrangement of S 2− in MoS 2 crystals and edges, these (S−S) 2− units are bridged between two Mo atoms at the edge of MoS 2 . 34,35 The abundant (S−S) 2− structures in MoS 2 -C and MoS 2 -C-3 are consistent with the XPS results. However, unlike MoS 2 -C, MoS 2 -C-3 exhibited a significantly higher hydrogen consumption between 200 and 600 °C.…”

Patterning edge-like defects and tuning defective areas on the basal plane of ultra-large MoS2 monolayers toward the hydrogen evolution reaction

“…The electrocatalytic activity was improved when bridging S 2 2− /apical S 2− increased on the surface, in agreement with other studies. 66 Among these two sites, bridging S 2 2− was theoretically found to have energy-favorable Gibbs free energy to drive the HER.…”

Introduction of MoS2–FeS2 with an S-Vacancy Defect as an Efficient Bifunctional Electrocatalyst for Hydrogen Evolution Reaction and Ferrocyanide and Iodide Oxidation Reactions

“…Electrolytic water splitting stands as a popular method for hydrogen production due to its simplicity, environmental friendliness, and high product purity. − However, the process, involving the hydrogen evolution reaction (HER) at the cathode and an oxygen evolution reaction (OER) at the anode, , typically operates at voltages exceeding the theoretical minimum , due to the sluggishness of the anodic OER. This inefficiency contributes to increased energy consumption and surplus oxygen production. − …”