Micromorphology engineering and co-catalyst construction are considered as feasible approaches to boost the photocatalytic hydrogen evolution performance. Herein, we combined two approaches to construct a new photocatalyst with titanium dioxide (TiO2) hierarchical microspheres (HMSs) as support and atomically dispersed platinum (Pt) species as co-catalyst (donated as TiO2 HMSs@xPt). The as-prepared TiO2 HMSs@xPt photocatalysts exhibited combined advantages including adequate light harvesting, improved charge-carrier separation and transport, abundant active sites, and reduced Pt consumption, which are favorable for photocatalytic hydrogen evolution. Specifically, the optimized TiO2 HMSs@0.36Pt exhibits a remarkable photocatalytic hydrogen evolution rate of 11.7 mmol g-1h-1 under simulated AM 1.5G solar light irradiation, which is 50 times and 4.8 times higher than those of pure TiO2 HMSs and traditional anatase TiO2 nanoparticles (NPs) with the same Pt loading, respectively.

Synthesizing urea from nitrate and carbon dioxide through an electrocatalysis approach under ambient conditions is extraordinarily sustainable. However, this approach still lacks electrocatalysts developed with high catalytic efficiencies, which is a key challenge. Here, we report the high-efficiency electrocatalytic synthesis of urea using indium oxyhydroxide with oxygen vacancy defects, which enables selective C-N coupling toward standout electrocatalytic urea synthesis activity. Analysis by operando synchrotron radiation-Fourier transform infrared spectroscopy showcases that *CO2NH2 protonation is the potential-determining step for the overall urea formation process. As such, defect engineering is employed to lower the energy barrier for the protonation of the *CO2NH2 intermediate to accelerate urea synthesis. Consequently, the defect-engineered catalyst delivers a high Faradaic efficiency of 51.0%. In conjunction with an in-depth study on the catalytic mechanism, this design strategy may facilitate the exploration of advanced catalysts for electrochemical urea synthesis and other sustainable applications.

Metal-free 2D phosphorus-based materials are emerging catalysts for ammonia (NH3 ) production through a sustainable electrochemical nitrogen reduction reaction route under ambient conditions. However, their efficiency and stability remain challenging due to the surface oxidization. Herein, a stable phosphorus-based electrocatalyst, silicon phosphide (SiP), is explored. Density functional theory calculations certify that the N2 activation can be realized on the zigzag Si sites with a dimeric end-on coordinated mode. Such sites also allow the subsequent protonation process via the alternating associative mechanism. As the proof-of-concept demonstration, both the crystalline and amorphous SiP nanosheets (denoted as C-SiP NSs and A-SiP NSs, respectively) are obtained through ultrasonic exfoliation processes, but only the crystalline one enables effective and stable electrocatalytic nitrogen reduction reaction, in terms of an NH3 yield rate of 16.12 µg h-1  mgcat. -1 and a Faradaic efficiency of 22.48% at -0.3 V versus reversible hydrogen electrode. The resistance to oxidization plays the decisive role in guaranteeing the NH3 electrosynthesis activity for C-SiP NSs. This surface stability endows C-SiP NSs with the capability to serve as appealing electrocatalysts for nitrogen reduction reactions and other promising applications.

The realization of long-range magnetic ordering in two-dimensional (2D) systems can potentially revolutionize next-generation information technology. Here, we report the successful fabrication of crystalline Cr3Te4 monolayers with room temperature ferromagnetism. Using molecular beam epitaxy, the growth of 2D Cr3Te4 films with monolayer thickness is demonstrated at low substrate temperatures ( 100C), compatible with Si CMOS technology. X-ray magnetic circular dichroism measurements reveal a Curie temperature (Tc) of 344 K for the Cr3Te4 monolayer with an out-of-plane magnetic easy axis, which decreases to 240 K for the thicker film ( 7 nm) with an in-plane easy axis. The enhancement of ferromagnetic coupling and the magnetic anisotropy transition is ascribed to interfacial effects, in particular the orbital overlap at the monolayer Cr3Te4/graphite interface, supported by density-functional theory calculations. This work sheds light on the low-temperature scalable growth of 2D nonlayered materials with room temperature ferromagnetism for new magnetic and spintronic devices.

AbstractEmulation of advanced synaptic functions of the human brain with electronic devices contributes an important step toward constructing high‐efficiency neuromorphic systems. Ferroelectric materials are promising candidates as synaptic weight elements in neural network hardware due to their controllable polarization states. However, the increased depolarization field at the nanoscale and the complex fabrication process of the traditional ferroelectric materials hamper the development of high‐density, low‐power, and highly sensitive synaptic devices. Here, we report the implementation of two‐dimensional (2D) ferroelectric α‐In2Se3 as an active channel material to emulate typical synaptic functions. The α‐In2Se3‐based synaptic device features multimode operations, enabled by the coupled ferroelectric polarization under various voltage pulses applied at both drain and gate terminals. Moreover, the energy consumption can be reduced to ~ 1 pJ by using high‐κ dielectric (Al2O3). The successful control of ferroelectric polarizations in α‐In2Se3 and its application in artificial synapses are expected to inspire the implementation of 2D ferroelectric materials for future neuromorphic systems.

Commercialization of the lithium-sulfur battery is hampered by bottlenecks like low sulfur loading, high cathode porosity, uncontrollable Li 2 S x deposition and sluggish kinetics of Li 2 S activation. Herein, we developed a densely stacked redox-active hexaazatrinaphthylene (HATN) polymer with a surface area of 302 m 2  g −1 and a very high bulk density of ca. 1.60 g cm −3 . Uniquely, HATN polymer has a similar redox potential window to S, which facilitates the binding of Li 2 S x and its transformation chemistry within the bulky polymer host, leading to fast Li 2 S/S kinetics. The compact polymer/S electrode presents a high sulfur loading of ca. 15 mg s  cm −2 (200-μm thickness) with a low cathode porosity of 41 %. It delivers a high areal capacity of ca. 14 mAh cm −2 and good cycling stability (200 cycles) at electrolyte–sulfur (E/S) ratio of 5 μL mg s −1 . The assembled pouch cell delivers a cell-level high energy density of 303 Wh kg −1 and 392 Wh L −1 .

Liquid-phase exfoliation can be developed for the large-scale production of two-dimensional materials for photonic applications. Although atomically thin 2D transition metal dichalcogenides (TMDs) show enhanced nonlinear optical properties or photoluminescence quantum yield relative to the bulk phase, these properties are weak in the absolute sense due to the ultrashort optical path, and they are also sensitive to layer-dependent symmetry properties. Another practical issue is that the chemical stability of some TMDs (e.g., Weyl semimetals) decreases dramatically as the thickness scales down to monolayer, precluding application as optical components in air. To address these issues, a way of exfoliating TMDs that ensures instantaneous passivation needs to be developed. Here, we employed a polymer-assisted electrochemical exfoliation strategy to synthesize PVP-passivated TMDs monolayers that could be spin coated and restacked into organic-inorganic superlattices with well-defined X-ray diffraction patterns. The segregation of restacked TMDs (e.g., MoS2) by PVP allows the inversion asymmetry of individual layers to be maintained in these superlattices, which allows second harmonic generation and photoluminescence to be linearly scaled with thickness. PVP-passivated monolayer 1T'-MoTe2 saturable absorber fabricated from these flakes exhibits fast response and recovery time (<150 fs) and pulse stability. Continuous-wave mode-locking based on 1T'-MoTe2 saturable absorber in a fiber ring laser cavity has been realized, attaining a fundamental repetition rate of 3.15 MHz and pulse duration as short as 867 fs at 1563 nm.

Abstract 2D ferroelectricity in van‐der‐Waals‐stacked materials such as indium selenide (In2Se3) has attracted interests because the ferroelectricity is robust even in ultrathin layers, which is useful for the miniaturization of ferroelectric field effect transistors. To implement In2Se3 in nanoscale ferroelectric devices, an understanding of the domain structure and switching dynamics in the 2D limit is essential. In this study, a biased scanning tunnelling microscopy (STM) tip is used to locally switch polarized domains in β′‐In2Se3, and the reconfiguration of these domains are directly visualized using STM. The room‐temperature surface of β′‐In2Se3 breaks into 1D nanostriped domains, which changes into a zig‐zag striped domains of β″ phase at low temperatures. These two types of domains can coexist, and by applying a tip‐sample bias, they can be interchangeably switched locally, showing volatile or nonvolatile like behavior depending on the threshold voltage applied. An atomic model is proposed to explain the switching mechanism based on tip‐induced flexoelectric effect and the ferroelastic switching between β′ and β″ phases.

Outside front cover image: Plasmonic effects in nanomaterials, metal nanoparticles in particular, have been applied in a variety of fields, such as plasmon-enhanced spectroscopies (e.g. surface-enhanced Raman scattering, surface-enhanced fluorescence, plasmon-enhanced optical activity…), photocatalysis, cancer therapy, etc. The performance of plasmonic nanometals can be further enhanced by combining them with metal-organic frameworks (MOFs), which feature well-defined pore size, large surface-area, diverse chemical/physical information, and efficient capture of specific molecules. The resulting hybrid nanomaterials, known as plasmonic MOFs, offer improved and further extended applications through a synergistic activity. Application-oriented topologies and compositions of plasmonic MOFs can be precisely controlled by means of thermodynamic and kinetic parameters during the synthetic process. (DOI: https://doi.org/10.1002/smm2.1047)

The breaking of multiple symmetries by periodic lattice distortion at a commensurate charge density wave (CDW) state is expected to give rise to intriguing interesting properties. However, accessing the commensurate CDW state on bulk TaS2 crystals typically requires cryogenic temperatures (77 K), which precludes practical applications. Here, we found that heteroepitaxial growth of a 2H-tantalum disulfide bilayer on a hexagonal-boron nitride (h-BN) substrate produces a robust commensurate CDW order at room temperature, characterized by a Moiré superlattice of 3 × 3 TaS2 on a 4 × 4 h-BN unit cell. The CDW order is confirmed by scanning transmission electron microscopy and Raman measurements. Theoretical calculations reveal that the stabilizing energy for the CDW phase of the monolayer and bilayer 2H-TaS2-on-h-BN substrates arises primarily from interfacial electrostatic interactions and, to a lesser extent, interfacial strain. Our work shows that engineering interfacial electrostatic interactions in an ultrathin van der Waals heterostructure constitutes an effective way to enhance CDW order in two-dimensional materials.

Chemical exfoliation has been used for the fast and large‐scale production of 2D nanosheets from graphene and transition metal dichalcogenides; however, it is rarely used for domain engineering of exfoliated nanosheets. Herein, it is found that the use of large sized molecular intercalants during electrochemical intercalation induce atomic row dislocation and parallel mirror twin boundaries (MTBs) on an otherwise pristine rhenium disulfide (ReS 2 ) crystal, such that the exfoliated flakes possess a parallel, multi‐domain structure. These domains can be distinguished under a polarized microscope owing to the intrinsic in‐plane optical dichroic properties of ReS 2 , thereby affording a way to track the number of domains introduced versus the size of the molecular intercalant during electrochemical exfoliation. Ferromagnetism is detected on the intercalated sample using large sized molecular intercalants. Density function theory suggests that these may be due to the coupled effects of lattice strain and S vacancies in the MTBs.

Among van der Waals layered ferromagnets, monolayer vanadium diselenide (VSe2 ) stands out due to its robust ferromagnetism. However, the exfoliation of monolayer VSe2 is challenging, not least because the monolayer flake is extremely unstable in air. Using an electrochemical exfoliation approach with organic cations as the intercalants, monolayer 1T-VSe2 flakes are successfully obtained from the bulk crystal at high yield. Thiol molecules are further introduced onto the VSe2 surface to passivate the exfoliated flakes, which improves the air stability of the flakes for subsequent characterizations. Room-temperature ferromagnetism is confirmed on the exfoliated 2D VSe2 flakes using a superconducting quantum interference device (SQUID), X-ray magnetic circular dichroism (XMCD), and magnetic force microscopy (MFM), where the monolayer flake displays the strongest ferromagnetic properties. Se vacancies, which can be ubiquitous in such materials, also contribute to the ferromagnetism of VSe2 , although density functional theory (DFT) calculations show that such effect can be minimized by physisorbed oxygen molecules or covalently bound thiol molecules.

With high theoretical energy density, rechargeable metal-gas batteries (e.g., Li-CO2 battery) are considered as one of the most promising energy storage devices. However, their practical applications are hindered by the sluggish reaction kinetics and discharge product accumulation during battery cycling. Currently, the solutions focus on exploration of new catalysts while the thorough understanding of their underlying mechanisms is often ignored. Herein, the interfacial electronic interaction within rationally designed catalysts, ZnS quantum dots/nitrogen-doped reduced graphene oxide (ZnS QDs/N-rGO) heterostructures, and their effects on transformation and deposition of discharge products in the Li-CO2 battery are revealed. In this work, the interfacial interaction can both enhance the catalytic activities of ZnS QDs/N-rGO heterostructures and induce the nucleation of discharge products to form a homogeneous Li2CO3/C film with excellent electronic transmission and high electrochemical activities. When the batteries cycle within a cutoff specific capacity of 1000 mAh g(-1) at a current density of 400 mA g(-1), the cycling performance of the Li-CO2 battery using a ZnS QDs/N-rGO cathode is over 3 and 9 times than those coupled with a ZnS nanosheets (NST)/N-rGO cathode and a N-rGO cathode, respectively. This work provides comprehensive understandings on designing catalysts for Li-CO2 batteries as well as other rechargeable metal-gas batteries.