Single-Atom Pt Anchored on Oxygen Vacancy of Monolayer Ti3C2Tx for Superior Hydrogen Evolution.

Two-dimensional (2D) MXene-loaded single-atom (SA) catalysts have drawn increasing attention. SAs immobilized on oxygen vacancies (OV) of MXene are predicted to have excellent catalytic performance; however, they have not yet been realized experimentally. Here Pt SAs immobilized on the OV of monolayer Ti3C2Tx flakes are constructed by a rapid thermal shock technique under a H2 atmosphere. The resultant Ti3C2Tx-PtSA catalyst exhibits excellent hydrogen evolution reaction (HER) performance, including a small overpotential of 38 mV at 10 mA cm-2, a high mass activity of 23.21 A mgPt-1, and a large turnover frequency of 23.45 s-1 at an overpotential of 100 mV. Furthermore, density functional theory calculations demonstrate that anchoring the Pt SA on the OV of Ti3C2Tx helps to decrease the binding energy and the hybridization strength between H atoms and the supports, contributing to rapid hydrogen adsorption-desorption kinetics and high activity for the HER.

Moiré bands in twisted trilayer black phosphorene: effects of pressure and electric field.

Twist-induced moiré bands and accompanied correlated phenomena have been extensively investigated in twisted hexagonal lattices with weak interlayer coupling. However, the formation of moiré bands in strongly coupled layered materials and their controlled tuning remain largely unexplored. Here, we systematically study the moiré bands in twisted trilayer black phosphorene (TTbP) and the influences of pressure and electric field on them. Moiré states can form in various TTbPs even when the twist angle is larger than 16° similar to that of twisted bilayer bP. However, different TTbPs show different localization patterns depending on the twisting layer, leading to distinct dipolar behaviors. While these moiré states become quasi-one-dimensional (1D) as the twist angle decreases, external pressure causes the crossover of moiré states from quasi-1D to 0D with a dramatic change in localization areas and greatly reduced bandwidth. Interestingly, compared to twisted bilayer and pristine bP, TTbPs show a much larger electric-field induced Stark effect, controllable by either the twist angle or twist layer. Our work thus demonstrates TTbP as an attractive platform to explore moiré-controlled electronic and optical properties, as well as tunable optoelectronic applications.

Single atom catalysts in Van der Waals gaps.

Single-atom catalysts provide efficiently utilized active sites to improve catalytic activities while improving the stability and enhancing the activities to the level of their bulk metallic counterparts are grand challenges. Herein, we demonstrate a family of single-atom catalysts with different interaction types by confining metal single atoms into the van der Waals gap of two-dimensional SnS2. The relatively weak bonding between the noble metal single atoms and the host endows the single atoms with more intrinsic catalytic activity compared to the ones with strong chemical bonding, while the protection offered by the layered material leads to ultrahigh stability compared to the physically adsorbed single-atom catalysts on the surface. Specifically, the trace Pt-intercalated SnS2 catalyst has superior long-term durability and comparable performance to that of commercial 10 wt% Pt/C catalyst in hydrogen evolution reaction. This work opens an avenue to explore high-performance intercalated single-atom electrocatalysts within various two-dimensional materials.

Anisotropic moiré optical transitions in twisted monolayer/bilayer phosphorene heterostructures.

Moiré superlattices of van der Waals heterostructures provide a powerful way to engineer electronic structures of two-dimensional materials. Many novel quantum phenomena have emerged in graphene and transition metal dichalcogenide moiré systems. Twisted phosphorene offers another attractive system to explore moiré physics because phosphorene features an anisotropic rectangular lattice, different from isotropic hexagonal lattices previously reported. Here we report emerging anisotropic moiré optical transitions in twisted monolayer/bilayer phosphorenes. The optical resonances in phosphorene moiré superlattice depend sensitively on twist angle and are completely different from those in the constitute monolayer and bilayer phosphorene even for a twist angle as large as 19°. Our calculations reveal that the Γ-point direct bandgap and the rectangular lattice of phosphorene give rise to the remarkably strong moiré physics in large-twist-angle phosphorene heterostructures. This work highlights fresh opportunities to explore moiré physics in phosphorene and other van der Waals heterostructures with different lattice configurations.