Phase-dependent growth of Pt on MoS for highly efficient H evolution.

Crystal phase is a key factor determining the properties, and hence functions, of two-dimensional transition-metal dichalcogenides (TMDs). The TMD materials, explored for diverse applications, commonly serve as templates for constructing nanomaterials and supported metal catalysts. However, how the TMD crystal phase affects the growth of the secondary material is poorly understood, although relevant, particularly for catalyst development. In the case of Pt nanoparticles on two-dimensional MoS nanosheets used as electrocatalysts for the hydrogen evolution reaction, only about two thirds of Pt nanoparticles were epitaxially grown on the MoS template composed of the metallic/semimetallic 1T/1T' phase but with thermodynamically stable and poorly conducting 2H phase mixed in. Here we report the production of MoS nanosheets with high phase purity and show that the 2H-phase templates facilitate the epitaxial growth of Pt nanoparticles, whereas the 1T' phase supports single-atomically dispersed Pt (s-Pt) atoms with Pt loading up to 10 wt%. We find that the Pt atoms in this s-Pt/1T'-MoS system occupy three distinct sites, with density functional theory calculations indicating for Pt atoms located atop of Mo atoms a hydrogen adsorption free energy of close to zero. This probably contributes to efficient electrocatalytic H evolution in acidic media, where we measure for s-Pt/1T'-MoS a mass activity of 85 ± 23 A [Formula: see text] at the overpotential of -50 mV and a mass-normalized exchange current density of 127 A [Formula: see text] and we see stable performance in an H-type cell and prototype proton exchange membrane electrolyser operated at room temperature. Although phase stability limitations prevent operation at high temperatures, we anticipate that 1T'-TMDs will also be effective supports for other catalysts targeting other important reactions.