Unsaturated bi-heterometal clusters in metal-vacancy sites of 2D MoS2 for efficient hydrogen evolution

The valence states and coordination structures of doped heterometal atoms in two-dimensional(2D)nanomaterials lack predictable regulation strategies.Hence,a robust method is proposed to form unsaturated heteroatom clusters via the metal-vacancy restraint mechanism,which can precisely regulate the bonding and valence state of heterometal atoms doped in 2D molybdenum disulfide.The unsaturated valence state of heterometal Pt and Ru cluster atoms form a spatial coordination structure with Pt–S and Ru–O–S as catalytically active sites.Among them,the strong binding energy of negatively charged suspended S and O sites for H+,as well as the weak adsorption of positively charged unsaturated heterometal atoms for H*,reduces the energy barrier of the hydrogen evolution reaction proved by theoretical calculation.Whereupon,the electrocatalytic hydrogen evolution performance is markedly improved by the ensemble effect of unsaturated heterometal atoms and highlighted with an overpotential of 84 mV and Tafel slope of 68.5 mV dec^(−1).In brief,this metal vacancy-induced valence state regulation of heterometal can manipulate the coordination structure and catalytic activity of heterometal atoms doped in the 2D atomic lattice but not limited to 2D nanomaterials.

Interface Effect of Ru-MoS_(2) Nanoflowers on Lignin Substrate for Enhanced Hydrogen Evolution Activity

The catalytic performance of Molybdenum disulfide(MoS_(2)) has been still far from that of Pt-based catalysts for inadequate active sites and sluggish electron transfer kinetics. Through engineering the interface between MoS_(2)-based materials and supported substrates, hybrid Ru-doped MoS_(2) on carbonized lignin(CL) is designed and prepared as efficient catalyst for hydrogen evolution reaction(HER). The CL substrate not only facilitates the growth of MoS_(2) nanoflowers, but also promotes the electron transfer. Ru doping increases active sites greatly for HER. The hybrid catalyst achieves a low onset overpotential of 25 mV and a low Tafel slope of 46 m V dec^(-1). The favorable HER activity ascribes to the interfacial interaction between MoS_(2) and CL. Density functional theory calculations further confirm the improved HER performance with doped Ru atoms. This study presents a prototype application to design electrocatalysts with enhanced carrier mobility and high-density active sites based on interface effect.

Gate tunable spatial accumulation of valley-spin in chemical vapor deposition grown 40°-twisted bilayer WS2

The emerging two-dimensional materials,particularly transition metal dichalcogenides(TMDs),are known to exhibit valley degree of freedom with long valley lifetime,which hold great promises in the implementation of valleytronic devices.Especially,light-valley interactions have attracted attentions in these systems,as the electrical generation of valley magnetization can be readily achieved—a rather different route toward magnetoelectric(ME)effect as compared to that from conventional electron spins.However,so far,the moiré patterns constructed with twisted bilayer TMDs remain largely unexplored in regard of their valley spin polarizations,even though the symmetry might be distinct from the AB stacked bilayer TMDs.Here,we study the valley Hall effect(VHE)in 40°-twisted chemical vapor deposition(CVD)grown WS2moiré transistors,using optical Kerr rotation measurements at 20 K.We observe a clear gate tunable spatial distribution of the valley carrier imbalance induced by the VHE when a current is exerted in the system.

High-performance lateral MoS2-MoO3 heterojunction phototransistor enabled by in-situ chemical oxidation

Construction of in-plane p-n junction with clear interface by using homogenous materials is an important issue in two-dimensional transistors,which have great potential in the applications of next-generation integrated circuit and optoelectronic devices.Hence,a controlled and facile method to achieve p-n interface is desired.Molybdenum sulfide(MoS2)has shown promising potential as an atomic-layer ntype semiconductor in electronics and optoelectronics.Here,we developed a facile and reliable approach to in-situ transform n-type MoS2 into p-type MoO3 to form lateral p-n junction via a KI/I2 solution-based chemical oxidization process.The lateral MoS2/MoO3 p-n junction exhibits a highly efficient photoresponse and ideal rectifying behavior,with a maximum external quantum efficiency of^650%,~3.6 mA W-1 at 0 V,and a light switching ratio of^102.The importance of the built-in p-n junction with such a high performance is further confirmed by high-resolution photocurrent mapping.Due to the high photoresponse at low source-drain voltage(VDS)and gate voltage(VG),the formed MoS2/MoO3 junction p-n diode shows potential applications in low-power operating photodevices and logic circuits.Our findings highlight the prospects of the local transformation of carrier type for high-performance MoS2-based electronics,optoelectronics and CMOS logic circuits.

Edge reconstruction of layer-dependentβ-In2Se3/MoS2 vertical heterostructures for accelerated hydrogen evolution

The layer-dependent properties are still unclarified in two-dimensional(2D)vertical heterostructures.In this study,we layer-bylayer deposited semimetalβ-In2Se3 on monolayer MoS2 to form verticalβ-In2Se3/MoS2 heterostructures by chemical vapor deposition.The defect-mediated nucleation mechanism inducesβ-In2Se3 nanosheets to grow on monolayer MoS2,and the layer number of stackedβ-In2Se3 can be precisely regulated from 1 layer(L)to 13 L by prolonging the growth time.Theβ-In2Se3/MoS2 heterostructures reveal tunable type-Ⅱband alignment arrangement by altering the layer number ofβ-In2Se3,which optimizes the internal electron transfer.Meanwhile,the edge atomic structure ofβ-In2Se3 stacking on monolayer MoS2 shows the reconstruction derived from large lattice mismatch(~29%),and the presence ofβ-In2Se3 also further increases the electrical conductivity ofβ-In2Se3/MoS2 heterostructures.Attributed to abundant layer-dependent edge active sites,edge reconstruction,improved hydrophilicity,and high electrical conductivity ofβ-In2Se3/MoS2 heterostructures,the edge ofβ-In2Se3/MoS2 heterostructures exhibits excellent electrocatalytic hydrogen evolution performance.Lower onset potential and smaller Tafel slope can be observed at the edge of monolayer MoS2 coupled with 13-Lβ-In2Se3.Hence,the outstanding conductive layers coupled with edge reconstruction in 2D vertical heterostructures play decisive roles in the optimization of electron energy levels and improvement of layer-dependent catalytic performance.

Challenges and opportunities in 2D high-entropy alloy electrocatalysts for sustainable energy conversion

Two-dimensional(2D)high-entropy alloys(HEAs)have emerged as promising electrocatalysts due to the benefits of polymetallic coordination and robust elec-trical conductivity.However,the multiple elements in 2D HEAs pose challenges in achieving a uniform composition and maintaining a 2D limit morphology,complicating their structural characterization.Furthermore,even minor adjust-ments to the composition can significantly alter the properties of 2D HEAs,underscoring the need for a deeper understanding of their structure-property relationships to advance synthesis and application.Therefore,this review crit-ically examines the intrinsic factors influencing synthesis methods and the practical applications of 2D HEAs in electrocatalysis for sustainable energy con-version.The urgency is emphasized for developing new synthesis techniques,enhancing advanced characterization methods,and gaining profound insights into the functional mechanisms of 2D HEAs.

Controllable preparation of 2D metal-semiconductor layered metal dichalcogenides heterostructures

1 Introduction Graphene is the first demonstration of a truly 2D atomic layer crystal, and has shown various excellent properties (e.g., ultrahigh carrier mobility, superior toughness, unique thermal conductivity, and good optics performance). The family of 2D crystals has grown to include metals (e.g., NbS2, VS2, TaS2), semiconductors (e.g., MoS2, WS2, ZrS2), and insulators (e.g., hexagonal boron nitride (hBN)), many of which are stable at ambient conditions [1]. 2D layered metal dichalcogenides (LMDs) materials [2].

由原子薄横向异质结构建的可调谐肖特基二极管

本研究利用一步化学气相沉积技术制备了Sn_(x)Mo_(1−x)S_(2)/MoS_(2)横向异质结高性能二极管.通过选择性掺杂Sn原子到单层MoS_(2)的边缘,形成了与MoS_(2)相同晶格常数的Sn_(x)Mo_(1−x)S_(2).在边缘的Sn_(x)Mo_(1−x)S_(2)和内部的MoS_(2)上分别沉积铬/金电极,形成肖特基势垒,其中势垒高度不同导致载流子仅在一个方向上传输.通过控制掺杂浓度和栅极电压,可实现MoS_(2)和Sn_(x)Mo_(1−x)S_(2)之间费米能级的对齐调节,实现了可调整的整流比,最高达到104.令人印象深刻的是,该二极管还表现出优异的光伏特性,该器件在λ=400 nm处实现了40%的外量子效率值.此外,我们在无外部偏压条件下实现了自供电光电探测,该异质结二极管在400和650 nm波长处的响应率分别为0.12和0.16 A W^(-1).对应的探测率分别是4.9×10^(10)和6.4×10^(10)Jones.可调的掺杂浓度为进一步创造高效器件提供了可能.这种合成二维侧向二极管的策略丰富了异质结二极管的材料多样性,并为开发新型电子和光电器件提供了新的平台.

S vacancies in 2D SnS_(2) accelerating hydrogen evolution reaction

Precise manipulation of atomic defects is essential for modulating the intrinsic properties of two-dimensional(2D)materials.In this study,sulfur(S)atoms are accurately knocked out in the 2D basal plane of pure tin disulfide(SnS_(2)).By varying the annealing temperatures(250–350℃),SnS_(2)with different S vacancy concentrations(Vs-SnS_(2))can be obtained.When SnS_(2)is annealed at 350℃ for 5 h,the S vacancies in the forms of single S atom and double S atoms could reach up to 30.5%.The Vs-SnS_(2)is tested in the microelectrocatalytic hydrogen evolution reaction(HER).Vs-SnS_(2)with S vacancies of 30.5%generates superior catalytic performance,with a Tafel slope of 74 mV dec^(-1) and onset potential of 141 mV.The mechanism has been proposed.First,computation confirms that the absence of S atoms prompts surface charge modulation and enhances electronic conductivity.In addition,the under-coordinated Sn atoms adjacent to S vacancy introduce the lattice distortion and charge density redistribution,which are beneficial to hydrogen binding in HER.In short,accurate knockout of specific atoms by controlling the annealing temperature is a promising strategy to explore structure-dependent properties of various 2D materials.