Ultrathin NiO/Ni_(3)S_(2)Heterostructure as Electrocatalyst for Accelerated Polysulfide Conversion in Lithium-Sulfur Batteries

The practical application of Lithium-Sulfur batteries largely depends on highly efficient utilization and conversion of sulfur under the realistic condition of high-sulfur content and low electrolyte/sulfur ratio.Rational design of heterostructure electrocatalysts with abundant active sites and strong interfacial electronic interactions is a promising but still challenging strategy for preventing shuttling of polysulfides in lithium-sulfur batteries.Herein,ultrathin nonlayered NiO/Ni_(3)S_(2)heterostructure nanosheets are developed through topochemical transformation of layered Ni(OH)_(2)templates to improve the utilization of sulfur and facilitate stable cycling of batteries.As a multifunction catalyst,NiO/Ni_(3)S_(2)not only enhances the adsorption of polysulfides and shorten the transport path of Li ions and electrons but also promotes the Li_(2)S formation and transformation,which are verified by both in-situ Raman spectroscopy and electrochemical investigations.Thus,the cell with NiO/Ni_(3)S_(2)as electrocatalyst delivers an area capacity of 4.8 mAh cm^(-2)under the high sulfur loading(6 mg cm^(-2))and low electrolyte/sulfur ratio(4.3 pL mg^(-1)).The strategy can be extended to 2D Ni foil,demonstrating its prospects in the construction of electrodes with high gravimetric/volumetric energy densities.The designed electrocatalyst of ultrathin nonlayered heterostructure will shed light on achieving high energy density lithium-sulfur batteries.

聚乳酸基层状纳米复合材料的研究进展

聚乳酸由于其良好的生物降解性、力学性能以及可加工性,具有极大的应用潜力,但是却面临脆性大、耐热温度低、阻燃性能差等缺点。而层状纳米材料是一类具有层状纳米结构,颗粒尺度为纳米或亚微米的纳米材料,具有优异的力学性能、热稳定性能、气体阻隔性能、电性能及化学性能。因此,使用层状纳米材料对聚乳酸进行改性,可以制备出具有优异性能的聚乳酸基纳米复合材料。文中重点综述了聚乳酸基层状硅酸盐、聚乳酸基层状双氢氧化物、聚乳酸基石墨烯及其衍生物3类纳米复合材料最新研究进展。

超支化聚酯对大麻纤维/天然橡胶复合材料性能的影响

采用超支化聚酯多元醇(BoltornTM P500)改善大麻纤维/天然橡胶(HF/NR)复合材料的界面结合,提高复合材料的力学性能。研究了P500对HF/NR复合材料力学性能的影响,并对P500在复合材料中的作用机制进行了探究。通过碱(NaOH)处理增加HF表面羟基(-OH)含量,进一步说明P500与HF之间的作用机制。力学性能测试结果表明,加入P500后HF/NR复合材料的力学性能提高明显。复合材料的拉伸强度从20.2 MPa提高至21.58 MPa,100%定伸应力从1.83 MPa增加至2.67 MPa,同时材料的断裂伸长率和撕裂强度也有不同程度的提高。扫描电镜、动态力学性能及橡胶加工分析发现,加入P500后复合材料中HF与NR之间的结合更加紧密。

二维材料最新研究进展

Research on two-dimensional(2D) materials has been explosively increasing in last seventeen years in varying subjects including condensed matter physics, electronic engineering, materials science, and chemistry since the mechanical exfoliation of graphene in 2004. Starting from graphene, 2D materials now have become a big family with numerous members and diverse categories. The unique structural features and physicochemical properties of 2D materials make them one class of the most appealing candidates for a wide range of potential applications. In particular, we have seen some major breakthroughs made in the field of 2D materials in last five years not only in developing novel synthetic methods and exploring new structures/properties but also in identifying innovative applications and pushing forward commercialisation. In this review, we provide a critical summary on the recent progress made in the field of 2D materials with a particular focus on last five years. After a brief backgroundintroduction, we first discuss the major synthetic methods for 2D materials, including the mechanical exfoliation, liquid exfoliation, vapor phase deposition, and wet-chemical synthesis as well as phase engineering of 2D materials belonging to the field of phase engineering of nanomaterials(PEN). We then introduce the superconducting/optical/magnetic properties and chirality of 2D materials along with newly emerging magic angle 2D superlattices. Following that, the promising applications of 2D materials in electronics, optoelectronics, catalysis, energy storage, solar cells, biomedicine, sensors, environments, etc. are described sequentially. Thereafter, we present the theoretic calculations and simulations of 2D materials. Finally, after concluding the current progress, we provide some personal discussions on the existing challenges and future outlooks in this rapidly developing field.

Enhanced mass transfer in three-dimensional single-atom nickel catalyst with open-pore structure for highly efficient CO_(2) electrolysis

Design of efficient catalysts for electrochemical reduction of carbon dioxide (CO_(2)) with high selectivity and activity is of great challenge, but significant for managing the global carbon balance. Herein, a series of three-dimensional (3D) single-atom metals anchored on graphene networks (3D SAM-G) with open-pore structure were successfully mass-produced via a facile in-situ calcination technique assisted by NaCl template. As-obtained 3D SANi-G electrode delivers excellent CO Faradaic efficiency (FE) of >96% in the potential range of −0.6 to −0.9 V versus reversible hydrogen electrode (RHE) and a high current density of 66.27 mA cm^(−2) at −1.0 V versus RHE, outperforming most of the previously reported catalysts tested in H-type cells. Simulations indicate that enhanced mass transport within the 3D open-pore structure effectively increases the catalytically active sites, which in turn leads to simultaneous enhancement on selectivity and activity of 3D SANi-G toward CO_(2) electroreduction. The cost-effective synthesis approach together with the microstructure design concept inspires new insights for the development of efficient electrocatalysts.

Boron-doping induced lithophilic transition of graphene for dendrite-free lithium growth

Li metal,possessing advantages of high theoretical specific capacity and low electrochemical potential,is regarded as the most promising anode material for next-generation batteries.However,despite decades of intensive research,its practical application is still hindered by safety hazard and low Coulombic efficiency,which is primarily caused by dendritic Li deposition.To address this issue,restraining dendrite growth at the nucleation stage is deemed as the most effective method.By utilizing the difference of electronegativity between boron atoms and carbon atoms,carbon atoms around boron atoms in boron-doped graphene(BG)turn into lithiophilic sites,which can enhance the adsorption capacity to Li^(+)at the nucleation stage.Consequently,an ultralow overpotential of 10 mV at a current density of 0.5 mA/cm^(2) and a high average Coulombic efficiency of 98.54%over more than 140 cycles with an areal capacity of 2 mAh/cm^(2) at a current density of 1 m A/cm^(2) were achieved.BG-Li|LiFePO_(4) full cells delivered a long lifespan of480 cycles at 0.5 C and excellent rate capability.This work provides a novel method for rational design of dendrite-free Li metal batteries by regulating nucleation process.

Large Rabi splitting obtained in Ag‐WS2 strong‐coupling heterostructure with optical microcavity at room temperature

Manipulation of light-matter interaction is critical in modern physics, especially in the strong coupling regime, where the generated half-light, half-matter bosonic quasiparticles as polaritons are important for fundamental quantum science and applications of optoelectronics and nonlinear optics. Two-dimensional transition metal dichalcogenides (TMDs) are ideal platforms to investigate the strong coupling because of their huge exciton binding energy and large absorption coefficients. Further studies on strong exciton-plasmon coupling by combining TMDs with metallic nanostructures have generated broad interests in recent years. However, because of the huge plasmon radiative damping, the observation of strong coupling is significantly limited at room temperature. Here, we demonstrate that a large Rabi splitting (~300 meV) can be achieved at ambient conditions in the strong coupling regime by embedding Ag-WS2 heterostructure in an optical microcavity. The generated quasiparticle with part-plasmon, part-exciton and part-light is analyzed with Hopfield coefficients that are calculated by using three-coupled oscillator model. The resulted plasmon-exciton polaritonic hybrid states can efficiently enlarge the obtained Rabi splitting, which paves the way for the practical applications of polaritonic devices based on ultrathin materials.

Contact engineering for two-dimensional semiconductors

Two-dimensional(2D)layered materials,including graphene,black phosphorus(BP)and transition metal dichalcogenide(TMD)such as molybdenum disulfide(Mo S2),tungsten diselenide(WSe2),have attracted increasing attention for the application in electronic and optoelectronic devices.Contacts,which are the communication links between these 2D materials and external circuitry,have significant effects on the performance of electronic and optoelectronic devices.However,the performance of devices based on 2D semiconductors(SCs)is often limited by the contacts.Here,we provide a comprehensive overview of the basic physics and role of contacts in 2D SCs,elucidating Schottky barrier nature and Fermi level pinning effect at metal/2D SCs contact interface.The progress of contact engineering,including traditional metals contacts and metallic 2D materials contacts,for improving the performance of 2D SCs based devices is presented.Traditional metal contacts,named 3D top and edge contacts,are discussed briefly.Meanwhile,methods of building 2D materials contacts(2D top contact and 2D edge contact)are discussed in detail,such as chemical vapor deposition(CVD)growth of 2D metallic material contacts,phase engineered metallic phase contacts and intercalation induced metallic state contacts.Finally,the challenges and opportunities of contact engineering for 2D SCs are outlined.

Phonon-assisted upconversion in twisted two-dimensional semiconductors

Phonon-assisted photon upconversion(UPC)is an anti-Stokes process in which incident photons achieve higher energy emission by absorbing phonons.This letter studies phonon-assisted UPC in twisted 2D semiconductors,in which an inverted contrast between UPC and conventional photoluminescence(PL)of WSe2 twisted bilayer is emergent.A 4-fold UPC enhancement is achieved in 5.5°twisted bilayer while PL weakens by half.Reduced interlayer exciton conversion efficiency driven by lattice relaxation,along with enhanced pump efficiency resulting from spectral redshift,lead to the rotation-angle-dependent UPC enhancement.The counterintuitive phenomenon provides a novel insight into a unique way that twisted angle affects UPC and light-matter interactions in 2D semiconductors.Furthermore,the UPC enhancement platform with various superimposable means offers an effective method for lighting bilayers and expanding the application prospect of 2D stacked van der Waals devices.

Temperature dependent Raman and photoluminescence of vertical WS2/MoS2 monolayer heterostructures

Heterostructures from two-dimensional transition-metal dichalcogenides MX_2 have emerged as a hot topic in recent years due to their various fascinating properties. Here, we investigated the temperature dependent Raman and photoluminescence(PL) spectra in vertical stacked WS_2/MoS_2 monolayer heterostructures. Our result shows that both E_(2g)~1 and A_(1g) modes of WS_2 and MoS_2 vary linearly with temperature increasing from 300 to 642 K. The PL measurement also reveals strong temperature dependencies of the PL intensity and peak position. The activation energy of the thermal quenching of the PL emission has been found to be equal to 69.6 meV. The temperature dependence of the peak energy well follows the bandgap shrinkage of bulk semiconductor.

Synthesis of large-scale atomic-layer SnS2 through chemical vapor deposition

Two-dimensional layers of metal dichalcogenides have attracted much attention because of their ultrathin thickness and potential applications in electronics and optoelectronics. Monolayer SnS2, with a band gap of -2.6 eV, has an octahedral lattice made of two atomic layers of sulfur and one atomic layer of tin. Till date, there have been limited reports on the growth of large-scale and high quality SnS2 atomic layers and the investigation of their properties as a semiconductor. Here, we report the chemical vapor deposition （CVD） growth of atomic-layer SnS2 with a large crystal size and uniformity. In addition, the number of layers can be changed from a monolayer to few layers and to bulk by changing the growth time. Scanning transmission electron microscopy was used to analyze the atomic structure and demonstrate the 2H stacking poly-type of different layers. The resultant SnS2 crystals is used as a photodetector with external quantum efficiency as high as 150%, suggesting promise for optoelectronic applications.

Synthesis of magnetic two-dimensional materials by chemical vapor deposition

The development of magnetic two-dimensional(2D)materials in its infancy has generated an enormous amount of attention as it offers an ideal platform for the exploration of magnetic properties down to the 2D limit,paving the way for spintronic devices.Due to the nonnegligible advantages including time efficiency and simplified process,the facile bottom-up chemical vapor deposition(CVD)is regarded as a robust method to fabricate ultrathin magnetic nanosheets.Recently,some ultrathin magnets possessing fascinating properties have been successfully synthesized via CVD.Here,the recent researches toward magnetic 2D materials grown by CVD are systematically summarized with special emphasis on the fabrication methods.Then,heteroatoms doping and phase transition induced in CVD growth to bring or tune the magnetic properties in 2D materials are discussed.Characterizations and applications of these magnetic materials are also discussed and reviewed.Finally,some perspectives in need of urgent attention regarding the development of CVD-grown magnetic 2D materials are proposed.

Recent advances of phase engineering in group VI transition metal dichalcogenides

As the crystal quality and phase structure of two-dimensional(2D)transition metal dichalcogenides(TMDs)have significant impacts on their properties such as electroconductivity,superconductivity and chemical stability,the precise synthesis,which plays an important role in fundamental researches and industrial applications,is highly required.Group VI TMDs,such as MoS_(2),usually exhibit diverse polymorphs including semiconducting 1H and metallic 1T phases.Even great efforts are devoted to revealing the structure-dependent physicochemical nature of TMDs by modulating their phases from the stable to the metastable at the atomic scale,there are still challenges on the phase-controlled synthesis of Group VI TMDs with metallic or semimetal properties.In this review,methods such as ion intercalation,chemical doping,strain engineering,defect triggering,and electric-field treatment are examined in detail.Finally,challenges and opportunities in this research field are proposed.

H_(2)S-assisted growth of 2D MS_(2)(M=Ti,Zr,Nb)

2D transition metal dichalcogenides (TMDCs) have drawn an enormous amount of attention due to their fascinating properties and application potential in next-generation information process and storage. However, the lack of proper synthesis approach limits their application. Here, we report a controllable synthesis method to grow ultrathin MS2 (M = Ti, Nb, Zr) nanosheets with H_(2)S-assisted chemical vapor deposition (CVD). We found that the presence of H_(2)S plays an important role to control the morphology of nanosheets including the lateral size and the nucleation density. With the assistance of H_(2)S, the growth of MS2 shows much thinner thickness with largely decreased nucleation density, beneficial for the device application, which can be attributed to the kinetics dominated growth. Our method hence opens a new avenue for the CVD growth of 2D TMDCs and the corresponding heterojunction, and paves the way for exploring their intriguing properties and applications.

Broadband light absorption and photoresponse enhancement in monolayer WSe_(2) crystal coupled to Sb_(2)O_(3) microresonators

Monolayer(1L)transition metal dichalcogenides(TMDCs)have been attracting tremendous interest in recent years as promising candidate materials in atomic-scale optoelectronic devices due to their direct band gaps(1.5-2.2 eV)and strong light-matter interactions.Unfortunately,their practical applications are limited by low visible light absorption stemming from atomic thickness and negligible infrared response.Here,we report the triangular Sb_(2)O_(3) microresonators in wide thickness and lateral size distributions grown on 1L TMDCs and their created significant broadband enhancement of light adsorption and photoresponse in 1L WSe_(2) crystal via coexisting Fabry-Perot and whispering gallery type resonances.As an example of demonstration,1L WSe_(2) crystal coupled to Sb_(2)O_(3) microresonators with widely distributed sizes exhibits the enhanced visible light absorption by up to 5 folds and the simultaneously extended near infrared(NIR)one of more than 50%.For application of 1L WSe_(2) in photodetection,incorporation of Sb2O3 microresonators leads to significantly enhanced visible light responsivity by~10^(4) order and expanded NIR one of more than 400 mA·W^(-1).Similar results have been observed in the other 1L W(Mo)dichalcogenides coupled to Sb2O3 microresonators.This work provides a new route for development of the high-performance monolayer TMDCs-based optoelectronic devices.

Thermodynamics of order and randomness in dopant distributions inferred from atomically resolved imaging

Exploration of structure-property relationships as a function of dopant concentration is commonly based on mean field theories for solid solutions.However,such theories that work well for semiconductors tend to fail in materials with strong correlations,either in electronic behavior or chemical segregation.In these cases,the details of atomic arrangements are generally not explored and analyzed.The knowledge of the generative physics and chemistry of the material can obviate this problem,since defect configuration libraries as stochastic representation of atomic level structures can be generated,or parameters of mesoscopic thermodynamic models can be derived.To obtain such information for improved predictions,we use data from atomically resolved microscopic images that visualize complex structural correlations within the system and translate them into statistical mechanical models of structure formation.Given the significant uncertainties about the microscopic aspects of the material’s processing history along with the limited number of available images,we combine model optimization techniques with the principles of statistical hypothesis testing.We demonstrate the approach on data from a series of atomically-resolved scanning transmission electron microscopy images of Mo_(x)Re_(1-x)S_(2) at varying ratios of Mo/Re stoichiometries,for which we propose an effective interaction model that is then used to generate atomic configurations and make testable predictions at a range of concentrations and formation temperatures.