Pd Sulfidation-Induced 1T-Phase Tuning in Monolayer MoS2 for Hydrogen Evolution Reaction

For single-atom-layer hydrogen evolution reaction catalysts, enrichment of the 1T-phase in monolayer molybdenum disulfide is important to achieve ideal metal utilization efficiency and exposure of active surface atoms. Herein, it is discovered that the 1T-phase degree in monolayer MoS2 can be enhanced through sulfidation of the Pd species deposited on MoS2 (PdxSy/1T-MoS2). Raman and X-ray photoelectron spectroscopy reveal that the sulfidation-assisted phase transition results in considerably greater proportions of 1T-phase fraction (up to 86%) without using alkali-metal-based approaches. Observations of S-atom displacement/translation at the atomic level contribute to the understanding of the phase transformation of MoS2. The maximized surface atom activation and metal utilization efficiency in PdxSy/1T-MoS2 lead to unprecedentedly high mass activity (-3444 A mg(Pd)(-1)) and turnover frequency (1892 s(-1)), three orders of magnitude higher than those of commercial Pt/C 10 wt% (3.6 A mg(Pt)(-1) and 3.6 s(-1)). The sulfidation-assisted 1T-phase enrichment has major implications for the designs of efficient electrocatalysts through MoS2 phase engineering.