Phase-dependent growth of Pt on MoS 2 for highly efficient H 2 evolution.

Crystal phase is a key factor determining the properties, and hence functions, of two-dimensional transition-metal dichalcogenides (TMDs) 1,2 . The TMD materials, explored for diverse applications 3-8 , commonly serve as templates for constructing nanomaterials 3,9 and supported metal catalysts 4,6-8 . 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 2 nanosheets used as electrocatalysts for the hydrogen evolution reaction 7 , only about two thirds of Pt nanoparticles were epitaxially grown on the MoS 2 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 2 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 2 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 2 evolution in acidic media, where we measure for s-Pt/1T'-MoS 2 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.