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

Abstract 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 MoS 2 can be enhanced through sulfidation of the Pd species deposited on MoS 2 (Pd x S y /1T‐MoS 2 ). 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 MoS 2 . The maximized surface atom activation and metal utilization efficiency in Pd x S y /1T‐MoS 2 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 MoS 2 phase engineering.