Engineering surface defects on layered PtTe ₂ and PdTe ₂ with reacting methanol

Abstract Transition metal dichalcogenides (TMDs), owing to their two-dimensional (2D) structures, could provide the largest active surface for reactions but consume minimal materials, so become potentially ideal catalysts. Structurally perfect basal planes of TMDs are typically inert whereas their surface defects can serve as catalytically active centers. The generation and control of such surface defects on TMDs thus become highly desired to manipulate their catalytic properties. We exposed PtTe ₂ and PdTe ₂ surfaces to methanol near ambient pressure to generate under-coordinated Pt and Pd (denoted as Pt _uc and Pd _uc respectively) at the surfaces. The generation, through the removal of surface Te (Te _s ), was triggered by a minimal methanol pressure about 10 ⁻³ mbar for Pt _uc (10 ⁻⁴ mbar for Pd _uc ) and enhanced with increased pressure, and attained a maximum about 10 ⁻² mbar for Pt _uc (5 × 10 ⁻³ mbar for Pd _uc ) at 300 K. The concentration of surface Pd _uc was tunable between 0% and 100% simply with an appropriate methanol pressure, despite varied initial concentrations of Te _s vacancies on as-prepared PdTe ₂ , whereas, in contrast, the Pt _uc was generated in a limited manner dependent on initial concentrations of Te _s vacancies ― the generation rate decreased at greater initial ones ― and their appreciable increase induced surface roughening. The Te _s was removed largely by the interaction of hydrogen atoms (H) from decomposed methanol with Te _s surrounding the vacancies, and subsequent formation and desorption of H ₂ Te. These results suggest, in addition to the known strategies of defect engineering, an alternative approach to engineer surface vacancies on layered 2D materials in a controllable manner.