Large Spin Hall Conductivity and Excellent Hydrogen Evolution Reaction Activity in Unconventional PtTe1.75 Monolayer

Two-Dimensional Topological Platinum Telluride Superstructures with Periodic Tellurium Vacancies for Efficient and Robust Catalysis

Defect engineering in the inherently inert basal planes of transition metal dichalcogenides (TMDs), involving the introduction of chalcogen vacancies, represents a pivotal approach to enhance catalytic activity by exposing high-density catalytic metal single-atom sites. However, achieving a single-atom limit spacing between chalcogen vacancies to form ordered superstructures remains challenging for creating uniformly distributed high-density metal single-atom sites on TMDs comparable to carbon-supported single-atom catalysts (SACs). Here we unveil an efficient TMD-based topological catalyst for hydrogen evolution reaction (HER), featuring high-density single-atom reactive centers on a few-layer (7 × 7)-PtTe2-x superstructure. Compared with pristine Pt(111), PtTe2, and (2 × 2)-PtTe2-x, (7 × 7)-PtTe2-x exhibits superior HER performance owing to its substantially increased density of undercoordinated Pt sites, alongside exceptional catalytic stability when operating at high current densities. First-principles calculations confirm that multiple types of undercoordinated Pt sites on (7 × 7)-PtTe2-x exhibit favorable hydrogen adsorption Gibbs free energies, and remain active upon increasing hydrogen coverage. Furthermore, (7 × 7)-PtTe2-x possesses nontrivial band topologies with robust edge states, suggesting potential enhancements for HER. Our findings are expected to advance TMD-based catalysts and exploration of topological materials in catalysis.

Evidence for Two-Dimensional Weyl Fermions in Air-Stable Monolayer PtTe1.75

The Weyl semimetals represent a distinct category of topological materials wherein the low-energy excitations appear as the long-sought Weyl Fermions. Exotic transport and optical properties are expected because of the chiral anomaly and linear energy-momentum dispersion. While three-dimensional Weyl semimetals have been successfully realized, the quest for their two-dimensional (2D) counterparts is ongoing. Here, we report the realization of 2D Weyl Fermions in monolayer PtTe1.75, which has strong spin-orbit coupling and lacks inversion symmetry, by combined angle-resolved photoemission spectroscopy, scanning tunneling microscopy, second harmonic generation, X-ray photoelectron spectroscopy measurements, and first-principles calculations. The giant Rashba splitting and band inversion lead to the emergence of three pairs of critical Weyl cones. Moreover, monolayer PtTe1.75 exhibits excellent chemical stability in ambient conditions, which is critical for future device applications. The discovery of 2D Weyl Fermions in monolayer PtTe1.75 opens up new possibilities for designing and fabricating novel spintronic devices.

Transition metals of Pt and Pd on the surface of topological insulator Bi2Se3

Transition metal catalysts supported on topological insulators are predicted to show improved catalytic properties due to the presence of topological surface states, which may float up to the catalysts and provide robust electron transfer. However, experimental studies of surface structures and corresponding catalytic properties of transition metal/topological insulator heterostructures have not been demonstrated so far. Here, we report the structures, chemical states, and adsorption behaviors of two conventional transition metal catalysts, Pt and Pd, on the surface of Bi2Se3, a common topological insulator material. We reveal that Pt forms nanoparticles on the Bi2Se3 surface. Moreover, the interaction between Pt and surface Se is observed. Furthermore, thermal dosing of O2 onto the Pt/Bi2Se3 heterostructure leads to no oxygen adsorption. Detailed scanning tunneling microscopy study indicates that Pt transforms into PtSe2 after the thermal process, thus preventing O2 from adsorption. For another transition metal Pd, it exhibits approximate layer-island growth on Bi2Se3, and Pd-Se interaction is also observed. Our work provides significant insights into the behaviors of transition metals on top of a common topological insulator material and will assist in the future design of catalysts built with topological materials.