Tailoring of 1T Phase-Domain MoS2 Active Sites with Bridging S22-/Apical S2- 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 S^2- 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 S^2- 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.