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As an emerging energy storage device, supercapacitor is widely investigated owing to its excellent capability, quick charge-discharge and tremendous cycle life. The operation potential window, energy density and mass loading of supercapacitor must be taken into deep consideration for its practical application. In this work, an outstanding electrode based on CFF@V2O5 nanosheets was prepared. Then a free-standing asymmetric supercapacitor with CFF@V2O5 composite as positive electrode and CFF@AC as negative electrode was assembled. Owing to the functional groups produced on CFF after the activation, V2O5 nanosheets was immobilized. The composite exhibits remarkable specific capabilities of 1465 mF cm−2 (492 F g−1). The energy density of the assembled free-standing asymmetric supercapacitor achieves 0.928 mWh cm−3 when the power density is 17.5 mW cm−3. After 6000 charging-discharging cycles as under normal, bended and anti-bended conditions for respective 2000 cycles, the device retains 89.7% of the initial capacitance, exhibiting fascinating cycle stabilization. Finally, two devices linked series can lighten a LED of 1.8 V for 2 min after charging for 2.5 min, which is inspiring for the practical application and production of self-supporting asymmetric supercapacitors.

As a new energy-storage device, a supercapacitor has attracted great attention, but its low power density limits its wide application. The key to develop high-performance supercapacitors is to find...

Copper oxide has aroused great concern in energy storage fields due to its properties of high theoretical capacitance, low cost and mild toxicity. However, its wide application still remains challenges owing to its poor electrical conductivity and unstable cycling life. Binder-free foam electrodes possess abundant porous structures and high specific surface area, which could get good contact with electrolyte. Herein, we demonstrate Ag nanoparticles decorated CuxO nanowires grown spontaneously on copper foam (CF) electrode for asymmetric supercapacitor. The skeleton structure of CF provides large amounts of active sites for the growth of CuxO nanowires. Moreover, Ag nanoparticles further decrease the internal resistance and enhance the electrochemical performance. Ag/CuxO/CF-40 electrode presents a high area specific capacitance of 1192 mF cm−2 at 2 mA cm−2 and the influence of surface capacitance-dominated process and diffusion-controlled process are discussed in detail. Besides, the energy density of the as-prepared asymmetric supercapacitor (ASC) reaches 46.32 μWh cm−2 at a power density of 3.00 mW cm−2. A 2V LED is lighted successfully by two ASC in series. This work provides a new strategy to prepare low internal resistance and binder-free flexible Ag/CuxO/CF electrode, which demonstrates a good potential application in flexible supercapacitors or other wearable electronic devices.

The periodic bulk structures of metal–organic frameworks (MOFs) can be solved by diffraction-based techniques; however, their non-periodic local structures—such as crystal surfaces, grain boundaries, defects, and guest molecules—have long been elusive due to a lack of suitable characterization tools. Recent advances in (scanning) transmission electron microscopy ((S)TEM) has made it possible to probe the local structures of MOFs at atomic resolution. In this article, we discuss why high-resolution (S)TEM of MOFs is challenging and how the new low-dose techniques overcome this challenge, and we review various MOF structural features observed by (S)TEM and important insights gained from these observations. Our discussions focus on real-space imaging, excluding other TEM-related characterization techniques (e.g. electron diffraction and spectroscopy). While the bulk structures of metal–organic frameworks can be solved by diffraction-based techniques, characterization of their local structures has been lacking. Here the authors review recent advances in (scanning) transmission electron microscopy that have made it possible to probe the local structures of MOFs at atomic resolution.

A composite containing self-assembled MoO2 nanoparticles and functional carbon nanosheets was obtained via a facile and controllable strategy. Two-dimensional functional carbon nanosheets as matrices have close contact with MoO2 nanoparticles, which assists in the improvement of electronic conductivity, provides efficient pathways and accelerates electron transfer. The carbon nanosheets have functional groups on the surface, which could serve as the nucleation sites for MoO2. The MC-0.12 composite shows optimal specific capacitance (190.9 F g-1 at 1 A g-1) and excellent cycle stability between monomers and composites with different constituents. The assembled symmetrical coin cell supercapacitor using MC-0.12 possesses the maximum energy density of 10.3 Wh kg-1 at a power density of 378 W kg-1 and still maintains the energy density of 7.9 Wh kg-1 at 1682 W kg-1 with a larger potential window. The capacitance retention (92%) of the assembled device is maintained after 2000 cycles, showing outstanding cycle life. Therefore, the integration of self-assembled MoO2 nanoparticles with 2D functional carbon nanosheets provides the composite superior electrochemical performance for supercapacitor applications.

Room-temperature manipulation and processing of information encoded in the electronic valley pseudospin and spin degrees of freedoms lie at the heart of the next technological quantum revolution. In atomically thin layers of transition-metal dichalcogenides (TMDs) with hexagonal lattices, valley-polarized excitations and valley quantum coherence can be generated by simply shining with adequately polarized light. In turn, the polarization states of light can induce topological Hall currents in the absence of an external magnetic field, which underlies the fundamental principle of opto-valleytronics devices. However, demonstration of optical generation of valley polarization at room temperature has remained challenging and not well understood. Here, we demonstrate control of strong valley polarization (valley quantum coherence) at room temperature of up to ∼50% (∼20%) by strategically designing Coulomb forces and spin-orbit interactions in atomically thin TMDs via chalcogenide alloying. We show that tailor making the carrier density and the relative order between optically active (bright) and forbidden (dark) states by key variations on the chalcogenide atom ratio allows full control of valley pseudospin dynamics. Our findings set a comprehensive approach for intrinsic and efficient manipulation of valley pseudospin and spin degree of freedom toward realistic opto-valleytronics devices.

Specific surface area and electrical conductivity are two decisive factors affecting materials properties. As a potential energy material, MoO3 is still limited in research and application due to its inherent defects. Ag nanoparticles with good electrical conductivity and unique small-size effect are predicted to have more hopeful prospects in energy storage. Ag@MoO3 composites with different Ag content were successfully prepared by a simple liquid-phase reduction method. The results show that the Ag@MoO3 composite has good morphology and the maximum capacitance (225 F/g) when the content of Ag is 8%. Notably, the internal resistance and Warberg resistance of the composite compared with that of MoO3 have been greatly reduced. It is mainly due to the high ion conductivity and small-size effect of Ag nanoparticles, which effectively improve the diffusion efficiency of ions between electrolyte and active materials. Practical application feasibility of Ag@MoO3 electrode was tested in the two-electrode system. Symmetrical coin cell supercapacitor using 8% Ag@MoO3 as electrodes has superior performance. Our work has potential reference value for the combination and characterization of energy storage materials.

The synergetic combination of double-layer capacitor carbon nanosheets and pseudocapacitive CuO particles with enhanced electrochemical properties had been proposed. Herein, CuO/carbon nanosheets electrode material with outstanding electrochemistry performance was successfully synthesized via a low-cost and controllable strategy. Such rational architecture integrates high-conductivity carbon nanosheets with rich-chemical-activity CuO particles. The surface-functional carbon nanosheets serve as a conductive substrate, provide an efficient pathway and accelerate the fast diffusion of electrons. This electrode material depicts high specific capacitance up to 183.9 and 371.1 F g−1 at 1 A g−1 in Na2SO4 and KOH electrolyte using three-electrode tests, respectively. Moreover, two symmetric devices using this CuO/carbon nanosheets electrode material were assembled with different electrolytes. The as-fabricated device with KOH electrolyte delivers remarkable energy density of 19.36 W h kg−1 at power density of 355.6 W kg−1 and still maintains 12.06 W h kg−1 at 1750.7 W kg−1. The as-fabricated device with Na2SO4 electrolyte achieves the maximum energy density of 12.46 W h kg−1 at 355.6 W kg−1. The capacitance retention rate is maintained at 94.4% after 2000 cycles in the as-fabricated coin cell supercapacitor with Na2SO4 electrolyte, showing outstanding long-cycling life. Herein, the strategic integration of CuO particles with two-dimensional functional carbon nanosheets as the electrode material provides superior electrochemical performance for supercapacitors.

Supercapacitors are considered to be a new promising green energy storage device owing to their excellent long cycle life. Compared with the conventional coating technique, the strategy of self-growing electrode materials on highly flexible collectors have become a new development trend. A binder-free and flexible electrode composed of vertical MoS 2 nanosheets arrays on carbon cloth was obtained via a convenient hydrothermal method. Carbon cloth, as a supporting substrate, effectively avoids the agglomeration of MoS 2 nanosheets and exposes more electrochemical active sites. The construction of binder-free electrode is an effective way to improve the electrochemical performance, which makes ions transfer faster. As a result, MoS 2 nanosheets arrays decorated carbon cloth shows high areal capacitance (2236.6 mF cm −2 at 10 mA cm −2 ) with favorable cycle stability (86.1% after 2000 cycles). To further explore the practical application of supercapacitors, symmetric coin cell (SCC) and all-solid-state supercapacitors (ASC) were assembled using MoS 2 /CC as working electrode. Due to the facile preparation, the excellent performance and the stable architecture, the vertical MoS 2 arrays decorated carbon cloth as binder-free electrode will be greatly developed in the field of flexible supercapacitors.

Noble metal nanocrystals (NCs) are often densely packed in their most stable forms that are determined by a combination of effects arising from the electronic, magnetic, geometric, and phononic properties of the NCs. These packing modes usually include the densest packed polytypes of Barlow packings and more open or distorted packings with slightly lower atomic packing factors. The structural modulation strategies of NCs towards the better performances for diverse applications are usually limited to the crystal size, shape, and surface control, which have been robustly studied and documented. An exciting emerging field related to structural engineering of noble metal NCs turns out to be the crystal phase control, which allows the chemical synthesis of energetically high-lying phases of NCs and leads to intriguing performances in catalysis and energy conversion. This article provides a comprehensive review of crystal phase regulation that endows both noble metal and noble-metal-based alloy NCs with unique electronic structures and enhanced performances. The basic principles, general design rationale, synthetic approaches, and structural characterizations for a variety of successful case studies related to crystal phase engineering are reviewed and discussed. In the end, the perspectives and challenges associated with the development of a more controllable chemical synthetic strategy towards the high-energy phases of noble metal NCs are put forward.

Summary Achieving high activity and long-term stability is a major challenge in the design of catalysts. In particular, the oxygen evolution reaction (OER) in acidic media, which plays a key role in proton exchange membrane electrolyzers for fast hydrogen fuel generation, seriously suffers from rapid degradation of catalysts as a result of the harsh acidic and oxidative conditions. Here, we report a rational design strategy for the fabrication of a heterostructured OER electrocatalyst (Ru@IrOx) that has unique physicochemical properties and in which a strong charge redistribution exists between a highly strained ruthenium core and a partially oxidized iridium shell across the metal-metal oxide heterojunction. The increased valence of the iridium shell and the decreased valence of the ruthenium core activate a synergistic electronic and structural interaction, which results in the enhanced activity and stability of the catalyst compared with the majority of the state-of-the-art ruthenium- and iridium-based materials.

The direct conversion of CO2 to syngas with controllable composition remains an intense interest for the production of renewable fuels. Large current density and high cell voltage efficiency are critical from a practical viewpoint for electrochemical CO2 reduction reaction (CRR), while the design of catalysts is a great challenge. Here, we report oxide-derived Cu nanowires with abundant, highly dispersed two-phase CuO heterostructures for syngas generation. The specified H2/CO ratios of 1, 2 and 3, with extra high CRR faradic (90%) and energetic (50%) efficiencies, were achieved. Density functional theory calculations reveal that the misfit dislocation sites in the electrocatalyst break the inherent scaling relationship of CRR intermediates' adsorption energies with an extraordinarily strong adsorption of *COOH and consequently promote excellent activity of the catalyst toward CRR. Driven by a commercial solar cell (working voltage of 2.2 V) under direct sunlight, the freestanding electrocatalyst can steadily generate syngas of the desired composition using CO2 as a feedstock.

Macromolecular films are crucial functional materials widely used in the fields of mechanics, electronics, optoelectronics, and biology, due to their superior properties of chemical stability, small density, high flexibility, and solution-processing ability. Their electronic and mechanical properties, however, are typically much lower than those of crystalline materials, as the macromolecular films have no long-range structural ordering. The state-of-the-art for producing highly ordered macromolecular films is still facing a great challenge due to the complex interactions between adjacent macromolecules. Here, the growth of textured macromolecular films on a designed graphene/high-index copper (Cu) surface is demonstrated. This successful growth is driven by a patterned potential that originates from the different amounts of charge transfer between the graphene and Cu surfaces with, alternately, terraces and step edges. The textured films exhibit a remarkable improvement in remnant ferroelectric polarization and fracture strength. It is also demonstrated that this growth mechanism is universal for different macromolecules. As meter-scale graphene/high-index Cu substrates have recently become available, the results open a new regime for the production and applications of highly ordered macromolecular films with obvious merits of high production and low cost.

Rh nanostructures composed of nanosheets embedded with nanodomains adopt vacated Barlow packing with ordered vacancies., Metallic nanostructures are commonly densely packed into a few packing variants with slightly different atomic packing factors. The structural aspects and physicochemical properties related with the vacancies in such nanostructures are rarely explored because of lack of an effective way to control the introduction of vacancy sites. Highly voided metallic nanostructures with ordered vacancies are however energetically high lying and very difficult to synthesize. Here, we report a chemical method for synthesis of hierarchical Rh nanostructures (Rh NSs) composed of ultrathin nanosheets, composed of hexagonal close-packed structure embedded with nanodomains that adopt a vacated Barlow packing with ordered vacancies. The obtained Rh NSs exhibit remarkably enhanced electrocatalytic activity and stability toward the hydrogen evolution reaction (HER) in alkaline media. Theoretical calculations reveal that the exceptional electrocatalytic performance of Rh NSs originates from their unique vacancy structures, which facilitate the adsorption and dissociation of H2O in the HER.

Vertically aligned noble metal nanowire arrays were grown on conductive electrodes based on a solution growth method. They show significant improvement of electrocatalytic activity in ethanol oxidation, from a re-deposited sample of the same detached nanowires. The unusual morphology provides open diffusion channels and direct charge transport pathways, in addition to the high electrochemically active surface from the ultrathin nanowires. Our best nanowire arrays exhibited much enhanced electrocatalytic activity, achieving a 38.0 fold increase in specific activity over that of commercial catalysts for ethanol electrooxidation. The structural design provides a new direction to enhance the electrocatalytic activity and reduce the size of electrodes for miniaturization of portable electrochemical devices.

Gold on activated carbon (Au/AC) materials are promising alternative catalysts for ethyne hydrochlorination. The preparation of active, stable Au/AC catalysts without aqua regia for ethyne hydrochlorination remains a significant challenge. A novel catalyst preparation protocol involving impregnation using a H 2 O 2 /HCl mixture is established for highly active Au/AC catalysts comprising primarily of single-site cationic Au species, as identified by systematic X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) analyses and transmission electron microscopy (TEM) imaging. In addition, evaluation of the Au-C interface by temperature-programmed desorption (TPD) analyses showed that the oxidation of activated carbon by the H 2 O 2 /HCl mixture, which creates surface oxygen-containing functional groups (SOGs), is a crucial step for the formation of active Au/AC catalysts. The structure determination and comprehensive experimental evidence allow density functional theory (DFT) to predict that single-site cationic AuCl species stabilized by SOGs via -O- linkages are efficient active sites for Au-catalyzed ethyne hydrochlorination. In addition, these catalysts can be reused for several times with negligible changes in performance after treatment with the H 2 O 2 /HCl mixture. The H 2 O 2 /HCl mixture is thus envisioned as a viable, green alternative to toxic aqua regia for the preparation of Au/AC catalysts for ethyne hydrochlorination.

The search for new superconductors capable of carrying loss-free current has been a research theme in condensed matter physics for the past decade. Among superconducting compounds, titanates have not been pursued as much as Cu2+ (3d9) (cuprate) and Fe2+ (3d6) (pnictide) compounds. Particularly, Ti3+-based compounds or electron systems with a special 3d1 filling are thought to be promising candidates as high-TC superconductors, but there has been no report on such pure Ti3+-based superconducting titanates. With the advent of thin-film growth technology, stabilizing new structural phases in single-crystalline thin films is a promising strategy to realize physical properties that are absent in the bulk counterparts. Herein, we report the discovery of unexpected superconductivity in orthorhombic-structured thin films of Ti2O3, a 3d1 electron system, which is in strong contrast to the conventional semiconducting corundum-structured Ti2O3. This is the first report of superconductivity in a titanate with a pure 3d1 electron configuration. Superconductivity at 8 K was observed in the orthorhombic Ti2O3 films. Leveraging the strong structure-property correlation in transition-metal oxides, our discovery introduces a previously unrecognized route for inducing emergent superconductivity in a newly stabilized polymorph phase in epitaxial thin films. Researchers have discovered a titanate -based single-crystal film with a rare structure that allows superconductivity to emerge at low temperatures. Titanium (III) oxide, Ti2O3, has garnered recent interest for solar and energy harvesting devices because its electrons are easily excited by electromagnetic radiation. A team led by Tom Wu from University of New South Wales in Sydney, Australia and Shuai Dong from Southeast University in Nanjing, China, report that these electrons have a very high density comparable to metals and are strongly coupled with lattice in constrained thin films. The researchers used a sapphire substrate to direct the growth of nanometer-thick Ti2O3 layers into a solid-state structure not normally found in free-grown crystals. One particular combination of growth temperature and film thickness yielded an orthorhombic crystal phase that exhibited an unusual semiconductor-to-superconductor electronic transition when cooled to 8 K. Polymorph-dependent superconductivity was discovered in orthorhombic-structured Ti2O3 thin films, which is in strong contrast to the conventional semiconducting trigonal corundum-structured Ti2O3. Leveraging on the strong structure-property correlation in transition-metal oxides, our discovery introduces a hitherto unrecognized route towards inducing superconductivity in 3d1 electron systems via polymorph engineering.

Unravelling the electrocatalytic activity origins of bimetallic nanomaterials is of great importance, yet fundamentally challenging. One of the main reasons for this is that the interactive contributions from geometric and electronic effects to enhancements in reaction activity are difficult to distinguish from one another. Here, on well-defined Ru–Pt core–shell (Ru@Pt) and homogeneous alloy (RuPt) model electrocatalysts, we are able to isolate these two effects. Furthermore, we observe the dominant role of strain in the intrinsic activity of the alkaline hydrogen evolution reaction. In the Ru@Pt icosahedral nanostructure, the highly strained Pt shells effectively accommodate the interfacial lattice mismatch from a face-centered cubic structured Ru core. This unique property leads to a weak binding of hydrogen and optimal interaction with hydroxyl species during the reaction, thus leading to an enhanced apparent activity of Ru@Pt.

The linker swing motion in the zeolitic imidazolate framework (ZIF-90) is investigated by density functional theory calculation and grand-canonical Monte Carlo simulations. The relation between the...

Hollowed single-crystal pre-perovskite PbTiO3 fibers (PP-PTF) were successfully synthesized via a polyvinyl alcohol (PVA) assisted hydrothermal process. The as-prepared PP-PTF were characterized to be 0.3–1 μm in diameter and tens of micrometers in length by adjusting the concentration of PVA to 0.8 g L−1. Microstructure characterization of the samples at different reaction times revealed that PP-PTF were formed via a three-dimensional (3D) hierarchical oriented attachment (OA) growth process. The initial growth units were determined to be single-crystal pre-perovskite PbTiO3 fibers with a diameter of 10–20 nm. Zeta potential measurement suggested that the main driving force of the OA process is the surface electrostatic force, which is induced by the incompletely bonded Pb and O atomic layers on the surface of the {110} plane. Moreover, molecular dynamics simulations have been employed to reveal a stable configuration of the initial pre-perovskite PbTiO3 growth units, agreeing well with the experimental results.

Carbon-supported ruthenium catalysts are promising mercury-free catalysts for acetylene hydrochlorination, due to their high activity and relatively low price. However, ruthenium catalysts often suffer from serious deactivation. Herein, a stable RuCl3-A/AC catalyst was prepared by applying a simple ammonia treatment during the impregnation process. The fresh and used ruthenium catalysts were comprehensively characterized using N2 sorption, NH3-temperature-programmed desorption (NH3-TPD), H2 temperature-programmed reduction (H2-TPR), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The results show that the RuCl3 species is identified as the active species, and the surface acidity of the RuCl3/AC catalyst is generated mainly from supported RuCl3 species, which can easily cause coke deposition. The enhancement of the stability of the RuCl3-A/AC catalyst is attributed to the formation of RuOx species and the decrease of the surface acidity.

Simultaneously improving the flexibility and electrochemical performance of electrode materials is a key issue to develop high-performance flexible all-solid-state supercapacitors. Herein, carbon cloth (CC) was applied as a flexible substrate and coated by MoS2 nanosheets through a hydrothermal method. Polypyrrole (PPy) was then deposited on MoS2 nanosheets by electrochemical deposition. Therefore, a novel PPy/MoS2/CC composite was prepared, in which PPy improves not only the capacitive performance, but also the rate capability and cycling stability significantly. The areal capacitance of PPy/MoS2/CC reaches 1150.4 mF cm−2 at 1 mA cm−2 and the specific capacitance retention can still maintain 87.2% after 5000 cycles (at 5 mA cm−2). It is worth mentioning that PPy/MoS2/CC was applied as working electrode to assemble a flexible all-solid-state symmetric supercapacitor. The device has a specific capacitance of 1016.4 mF cm−2 at 2 mA cm−2 and an energy density of 1.412 mWh cm−3 at the power density of 10 mW cm−3, which has outstanding application value for the development of flexible wearable devices.

The strong metal–support interactions (SMSI) are well-known but crucial for preparation of supported metal nanoparticle catalysts, which generally occur by reduction and oxidation under harsh conditions. Here, we delineate the example of constructing SMSI without reduction and oxidation, where the key is to employ a hydroxide-to-oxide support transformation. The covering of Au nanoparticles by oxides, electronic interaction, and changes in CO adsorption tests of the catalyst are identical to those of the classic SMSI. Owing to the SMSI with oxide barriers on the Au nanoparticles, the supported Au catalysts are sintering-resistant at high temperatures, which benefit long-life reactions, outperforming the conventional supported catalysts.

Metal nanocatalysts hold great promise for a wide range of heterogeneous catalytic reactions, while the optimization strategy of catalytic activity is largely restricted by particle size or shape control. Here, we demonstrate that a reversible microstructural control through the crossover between multiply twinned nanoparticle (MTP) and single crystal (SC) can be readily achieved by solvent post-treatment on gold nanoparticles (AuNPs). Polar solvents (e.g., water, methanol) direct the transformation from MTP to SC accompanied by the disappearance of twinning and stacking faults. A reverse transformation from SC to MTP is achieved in nonpolar solvent (e.g., toluene) mixed with thiol ligands. The transformation between two different microstructures is directly observed by in situ TEM and leads to a drastic modulation of catalytic activity toward the gas-phase selective oxidation of alcohols. On the basis of the combined experimental and theoretical investigations of alcohol chemisorption on these nanocatalysts, we propose that the exposure of {211}-like microfacets associated with twin boundaries and stack faults accounts for the strong chemisorption of alcohol molecules on MTP AuNPs and thus the exceptionally high catalytic activity.

Zero-dimensional perovskite-related structures (0D-PRS) are a new frontier of perovskite-based materials. 0D-PRS, commonly synthesized in powder form, manifest distinctive optical properties such as strong photoluminescence (PL), narrow emission line width, and high exciton binding energy. These properties make 0D-PRS compelling for several types of optoelectronic applications, including phosphor screens and electroluminescent devices. However, it would not be possible to rationally design the chemistry and structure of these materials, without revealing the origins of their optical behavior, which is contradictory to the well-studied APbX3 perovskites. In this work, we synthesize single crystals of Cs4PbBr6 0D-PRS, and investigated the origins of their unique optical and electronic properties. The crystals exhibit a PL quantum yield higher than 40%, the highest reported for perovskite-based single crystals. Time-resolved and temperature dependent PL studies, supported by DFT calculations, and structural ...

Rational design and synthesis of heterostructures based on transition metal dichalcogenides (TMDs) have attracted increasing interests because of their promising applications in electronics, catalysis, etc. However, the construction of epitaxial heterostructures with an interface at the edges of TMD nanosheets (NSs) still remains a great challenge. Here, we report a strategy for controlled synthesis of a new type of heterostructure in which TMD NSs, including MoS2 and MoSe2, vertically grow along the longitudinal direction of one-dimensional (1D) Cu2–xS nanowires (NWs) in an epitaxial manner. The obtained Cu2–xS-TMD heterostructures with tunable loading amount and lateral size of TMD NSs are achieved by the consecutive growth of TMD NSs on Cu2–xS NWs through gradual injection of chalcogen precursors. After cation exchange of Cu in Cu2–xS-TMD heterostructures with Cd, the obtained CdS–MoS2 heterostructures retained their original architectures. Compared to the pure CdS NWs, the CdS–MoS2 heterostructures wi...

The ability to prepare ultrathin two-dimensional (2D) covalent organic framework (COF) nanosheets (NSs) in high yield is of great importance for the further exploration of their unique properties and potential applications. Herein, by elaborately designing and choosing two flexible molecules with C3v molecular symmetry as building units, a novel imine-linked COF, namely, TPA-COF, with a hexagonal layered structure and sheet-like morphology, is synthesized. Since the flexible building units are integrated into the COF skeletons, the interlayer stacking becomes weak, resulting in the easy exfoliation of TPA-COF into ultrathin 2D NSs. Impressively, for the first time, the detailed structural information, i.e., the pore channels and individual building units in the NSs, is clearly visualized by using the recently developed low-dose imaging technique of transmission electron microscopy (TEM). As a proof-of-concept application, the obtained ultrathin COF NSs are used as a novel fluorescence sensing platform for...

We present a detailed study of post-deposition annealing effects on contact resistance of Au, Ti, Hf and Ni electrodes on Mg 2 Si thin films. Thin-film Mg 2 Si and metal contacts were deposited using magnetron sputtering. Various post-annealing temperatures were studied to determine the thermal stability of each contact metal. The specific contact resistivity (SCR) was determined using the Cross Bridge Kelvin Resistor (CBKR) method. Ni contacts exhibit the best thermal stability, maintaining stability up to 400 °C, with a SCR of approximately 10 −2 Ω-cm 2 after annealing. The increased SCR after high temperature annealing is correlated with the formation of a Mg-Si-Ni mixture identified by cross-sectional scanning transmission electron microscopy (STEM) characterization, X-ray diffraction characterization (XRD) and other elemental analyses. The formation of this Mg-Si-Ni mixture is attributed to Ni diffusion and its reaction with the Mg 2 Si film.

Organometallic complexes with metal–nitrogen/carbon (M–N/C) coordination are the most important alternatives to precious metal catalysts for oxygen reduction and evolution reactions (ORR and OER) in energy conversion devices. Here, we designed and developed a range of molecule-level graphitic carbon nitride (g-C3N4) coordinated transition metals (M–C3N4) as a new generation of M–N/C catalysts for these oxygen electrode reactions. As a proof-of-concept example, we conducted theoretical evaluation and experimental validation on a cobalt–C3N4 catalyst with a desired molecular configuration, which possesses comparable electrocatalytic activity to that of precious metal benchmarks for the ORR and OER in alkaline media. The correlation of experimental and computational results confirms that this high activity originates from the precise M–N2 coordination in the g-C3N4 matrix. Moreover, the reversible ORR/OER activity trend for a wide variety of M−C3N4 complexes has been constructed to provide guidance for the m...

While theoretical simulations predict contradictory results about how the intercalation of foreign metal atoms affects the order of atomic layers in black phosphorus (BP), no direct experimental visualization work has yet clarified this ambiguity. By in situ electrochemical sodiation of BP inside a high-resolution transmission electron microscope and first-principles calculations, we found that sodium intercalation induces a relative glide of 1/2 ⟨010⟩ {001}, resulting in reordering of atomic stacks from AB to AC in BP. The observed local amorphization in our experiments is triggered by lattice constraints. We predict that intercalation of sodium or other metal atoms introduces n-type carriers in BP. This potentially opens a new field for two-dimensional electronics based on BP.

Perovskite lead titanate nanostructures with specific {111}, {100} and {001} facets exposed, have been employed as supports to investigate the crystal facet effect on the growth and CO catalytic activity of Pt nanoparticles. The size, distribution and surface chemical states of Pt on the perovskite supports have been significantly modified, leading to a tailored conversion temperature and catalytic kinetics towards CO catalytic oxidation.

Cokes are inevitably generated during zeolite-catalyzed reactions as deleterious side products that deactivate the catalyst. In this study, we in situ converted cokes into carbons within the confined microporous zeolite structures and evaluated their performances as absorbing materials for solar-driven water evaporation. With a properly chosen zeolite, the coke-derived carbons possessed ordered interconnected pores and tunable compositions. We found that the porous structure and the oxygen content in the as-prepared carbons had important influences on their energy conversion efficiencies. Among various investigated carbon materials, the carbon derived from the methanol-to-olefin reaction over zeolite beta gave the highest conversion efficiency of 72% under simulated sunlight with an equivalent solar intensity of 2 suns. This study not only demonstrates the great potential of traditionally useless cokes for solar thermal applications but also provides new insights into the design of carbon-based absorbing materials for efficient solar evaporation.

A good resistance against mechanical stress is essential for the utilization of metal–organic frameworks (MOFs) in practical applications such as gas sorption, separation, catalysis or energy conversion. Here, we report on the successful modification of the mechanical properties of zeolitic imidazolate frameworks (ZIFs) achieved through a substitution of the terminal group. The mechanical modulus of SALEM-2 was found to significantly improve when the –H groups at position 2 of the imidazole linkers were replaced with electron withdrawing groups (–CHO, –Cl, or –Br). The charge distribution and electron density were analyzed to reveal the mechanism behind the observed variation of the elastic stiffness. Furthermore, ZIF-I with a –I group at position 2 of the imidazole linkers was predicted to exhibit an excellent mechanical strength in our study and then prepared experimentally. The results indicate that an inconspicuous change of the structure of ZIFs, i.e., additional groups strengthening the ZnN4 tetrahedron, will lead to a stiffer framework.

Water electrolysis represents a promising solution for storage of renewable but intermittent electrical energy in hydrogen molecules. This technology is however challenged by the lack of efficient electrocatalysts for the hydrogen and oxygen evolution reactions. Here we report on the synthesis of platinum-nickel hydroxide nanocomposites and their electrocatalytic applications for water reduction. An in situ reduction strategy taking advantage of the Ni(II)/Ni(III) redox has been developed to enable and regulate the overgrowth of Pt nanocrystals on single-layer Ni(OH) 2 nanosheets. The obtained nanocomposites (denoted as Pt@2D-Ni(OH) 2 ) exhibit an improvement factor of 5 in catalytic activity and a reduction of up to 130 mV in overpotential compared to Pt for the hydrogen evolution reaction (HER). A combination of electron microscopy/spectroscopy characterizations, electrochemical studies and density function theory calculations was employed to uncover the structures of the metal-hydroxide interface and understand the mechanisms of catalytic enhancement.

The application of electrochemical energy storage materials to capacitive deionization (CDI), a low-cost and energy-efficient technology for brackish water desalination, has recently been proven effective in solving problems of traditional CDI electrodes, i.e., low desalination capacity and incompatibility in high salinity water. However, Faradaic electrode materials suffer from slow salt removal rate and short lifetime, which restrict their practical usage. Herein, a simple strategy is demonstrated for a novel tubular-structured electrode, i.e., polyaniline (PANI)-tube-decorated with Prussian blue (PB) nanocrystals (PB/PANI composite). This composite successfully combines characteristics of two traditional Faradaic materials, and achieves high performance for CDI. Benefiting from unique structure and rationally designed composition, the obtained PB/PANI exhibits superior performance with a large desalination capacity (133.3 mg g-1 at 100 mA g-1 ), and ultrahigh salt-removal rate (0.49 mg g-1 s-1 at 2 A g-1 ). The synergistic effect, interfacial enhancement, and desalination mechanism of PB/PANI are also revealed through in situ characterization and theoretical calculations. Particularly, a concept for recovery of the energy applied to CDI process is demonstrated. This work provides a facile strategy for design of PB-based composites, which motivates the development of advanced materials toward high-performance CDI applications.

Achieving rapid definitive hemostasis is essential to ensure survival of patients with massive bleeding in pre-hospital care. It is however challenging to develop hemostatic agents or dressings that simultaneously deliver a fast, long-lasting and safe treatment of hemorrhage. Here, we integrate meso-/micro-porosity, blood coagulation and stability into a flexible zeolite-cotton hybrid hemostat. We employ an on-site template-free growth route that tightly binds mesoporous single-crystal chabazite zeolite onto the surface of cotton fibers. This hemostatic material maintains high procoagulant activity after water flow treatment. Chabazite particles are firmly anchored onto the cotton surface with, Zeolites have attracted attention and have been applied as haemostatic agents; however, there are issues associated with released zeolite powder. Here, the authors report on the growth of zeolites on cotton fibres with high stability and haemostatic ability.

Impurities produced during the synthesis process of a material pose detrimental impacts upon the intrinsic properties and device performances of the as-obtained product. This effect is especially pronounced in graphene, where surface contamination has long been a critical, unresolved issue, given graphene’s two-dimensionality. Here we report the origins of surface contamination of graphene, which is primarily rooted in chemical vapour deposition production at elevated temperatures, rather than during transfer and storage. In turn, we demonstrate a design of Cu substrate architecture towards the scalable production of super-clean graphene (>99% clean regions). The readily available, super-clean graphene sheets contribute to an enhancement in the optical transparency and thermal conductivity, an exceptionally lower-level of electrical contact resistance and intrinsically hydrophilic nature. This work not only opens up frontiers for graphene growth but also provides exciting opportunities for the utilization of as-obtained super-clean graphene films for advanced applications., The intrinsic properties of graphene and the resulting device performance are hindered by the impurities produced during the synthesis process. Here, the authors elucidate the origin of contaminations in CVD-grown graphene and devise a strategy towards the scalable production of ultra-clean graphene with >99% clean regions and low contact resistance.

At present, it is still a challenge for developing hybrid supercapacitors with outstanding electrochemical performance. Herein, a step-by-step approach was tailored to fabricate a novel electrode material as nickel-vanadium layered double hydroxide (NiV-LDH)@Co2NiO4 nano-coral arrays anchored on nickel foam. Thanks to the three-dimensional interconnected nanostructure, the electrode fully immersed in electrolyte participates in faradaic redox reaction, which promotes the transfer of ions and charges, leading to the enhancement of electrochemical performance. The optimal NiV-LDH@Co2NiO4/NF (nickel foam) exhibits 1381.8 C g−1 at 1 A g−1, which is the best among the prepared samples (compared with NiV-LDH/NF and Co2NiO4/NF). Benefitting from the coral-like interconnect morphology, NiV-LDH@Co2NiO4/NF retains 79.8% of the initial capacity after 5000 cycles at 5 A g−1. Besides, NiV-LDH@Co2NiO4/NF and activated carbon (AC) act as positive and negative electrodes, assembling a hybrid asymmetric supercapacitor, which delivers an ideal energy density of 68.7 W h kg−1 at a power density of 878.6 W kg−1 and leaves 88.6% of specific capacity remaining after 5000 cycles. To evaluate the practical application of NiV-LDH@Co2NiO4/NF//AC, two devices are connected in series and acted as a continuous energy supply for a 2.2 V LED light.

The rational synthesis of hierarchical three-dimensional nanostructures with specific compositions, morphologies and functionalities is important for applications in a variety of fields ranging from energy conversion and electronics to biotechnology. Here, we report a seeded growth approach for the controlled epitaxial growth of three types of hierarchical one-dimensional (1D)/two-dimensional (2D) nanostructures, where nanorod arrays of II-VI semiconductor CdS or CdSe are grown on the selective facets of hexagonal-shaped nanoplates, either on the two basal facets of the nanoplate, or on one basal facet, or on the two basal facets and six side facets. The seed engineering of 2D hexagonal-shaped nanoplates is the key factor for growth of the three resulting types of 1D/2D nanostructures. The wurtzite- and zinc-blende-type polymorphs of semiconductors are used to determine the facet-selective epitaxial growth of 1D nanorod arrays, resulting in the formation of different hierarchical three-dimensional (3D) nanostructures.

Direct synthesis of hierarchical zeolites currently relies on the use of surfactant-based templates to produce mesoporosity by the random stacking of 2D zeolite sheets or the agglomeration of tiny zeolite grains. The benefits of using nonsurfactant polymers as dual-function templates in the fabrication of hierarchical zeolites are demonstrated. First, the minimal intermolecular interactions of nonsurfactant polymers impose little interference on the crystallization of zeolites, favoring the formation of 3D continuous zeolite frameworks with a long-range order. Second, the mutual interpenetration of the polymer and the zeolite networks renders disordered but highly interconnected mesopores in zeolite crystals. These two factors allow for the synthesis of single-crystalline, mesoporous zeolites of varied compositions and framework types. A representative example, hierarchial aluminosilicate (meso-ZSM-5), has been carefully characterized. It has a unique branched fibrous structure, and far outperforms bulk aluminosilicate (ZSM-5) as a catalyst in two model reactions: conversion of methanol to aromatics and catalytic cracking of canola oil. Third, extra functional groups in the polymer template can be utilized to incorporate desired functionalities into hierarchical zeolites. Last and most importantly, polymer-based templates permit heterogeneous nucleation and growth of mesoporous zeolites on existing surfaces, forming a continuous zeolitic layer. In a proof-of-concept experiment, unprecedented core–shell-structured hierarchical zeolites are synthesized by coating mesoporous zeolites on the surfaces of bulk zeolites.

Rapid developing flexible electronics, such as flexible screens, sensors and wearable devices, make them forward to invent portable and flexible energy storage systems. Flexible supercapacitors possess quick charge-discharge, high power density, environmentally friendly and flexible characteristics, which highly cater to the growing market demands. In supercapacitors, electrolyte is one of the key factors affecting their performance. Herein, we demonstrate that a self-assembly Mn3O4/carbon cloth (Mn3O4/CC) electrode is synthesized successfully by a two-step hydrothermal method. In a three electrodes system, the Mn3O4/CC electrode is tested in Na2SO4 and KOH respectively. The results reveal that Mn3O4/CC exhibits higher specific capacitance (555 mF cm−2 at 1 mA cm−2) and lower internal resistance in KOH. On the other hand, it expresses nearly no loss in the cycle stability test (99% retention after 2000 cycles) in Na2SO4. The all-solid-state asymmetric supercapacitor presents a maximum energy density reaching 25 μWh cm−2 with a power density of 0.64 mW cm−2. It also presents ultra-high flexibility (bending and twisting for 200 times) and superior cycling performance (99.3% after 2000 cycles). Hence, the Mn3O4/CC electrode is of great prospect in the application of flexible electronic devices.

W.S., Q.P., and Q.C. contributed equally to this work. Y.Z. acknowledges the financial support from the National Natural Science Foundation of China (Grant No. 51701181), the Zhejiang Provincial Natural Science Foundation of China (Grant No. LR18B030003), and the Thousand Talents Program for Distinguished Young Scholars. Q.C. acknowledges the financial support from the National Natural Science Foundation of China (Grant No. 21905247).

Electron microscopy allows the extraction of multidimensional spatiotemporally correlated structural information of diverse materials down to atomic resolution, which is essential for figuring out their structure-property relationships. Unfortunately, the high-energy electrons that carry this important information can cause damage by modulating the structures of the materials. This has become a significant problem concerning the recent boost in materials science applications of a wide range of beam-sensitive materials, including metal-organic frameworks, covalent-organic frameworks, organic-inorganic hybrid materials, 2D materials, and zeolites. To this end, developing electron microscopy techniques that minimize the electron beam damage for the extraction of intrinsic structural information turns out to be a compelling but challenging need. This article provides a comprehensive review on the revolutionary strategies toward the electron microscopic imaging of beam-sensitive materials and associated materials science discoveries, based on the principles of electron-matter interaction and mechanisms of electron beam damage. Finally, perspectives and future trends in this field are put forward.

A trilayer single-crystalline GDY film on graphene was prepared through a solution-phase van der Waals epitaxial strategy., Graphdiyne (GDY) is an ordered two-dimensional (2D) carbon allotrope comprising sp- and sp2-hybridized carbon atoms with high degrees of π-conjugation, which features a natural band gap and superior electric properties. However, the synthesis of one- or few-layer GDY remains challenging because of the free rotation around alkyne-aryl single bonds and the lack of thickness control. We report the facile synthesis of an ultrathin single-crystalline GDY film on graphene through a solution-phase van der Waals epitaxial strategy. The weak admolecule-substrate interaction at the heterojunction drastically relaxes the large lattice mismatch between GDY and graphene. It allows the fast in-plane coupling of admolecules and slow out-of-plane growth toward the formation of an incommensurately stacked heterostructure, which is composed of single-layer graphene and few-layer ABC-stacked GDY, as directly observed by electron microscopy and identified from Raman fingerprints. This study provides a general route not only to the bottom-up synthesis of intriguing 2D acetylenic carbon allotropes but also to the device fabrication for the direct measurement of their intrinsic electrical, mechanical, and thermal properties.

Atomically dispersed supported metal catalysts are drawing wide attention because of the opportunities they offer for new catalytic properties combined with efficient use of the metals. We extend this class of materials to catalysts that incorporate atomically dispersed metal atoms as promoters. The catalysts are used for the challenging nitroarene hydrogenation and found to have both high activity and selectivity. The promoters are single-site Sn on TiO2 supports that incorporate metal nanoparticle catalysts. Represented as M/Sn-TiO2 (M = Au, Ru, Pt, Ni), these catalysts decidedly outperform the unpromoted supported metals, even for hydrogenation of nitroarenes substituted with various reducible groups. The high activity and selectivity of these catalysts result from the creation of oxygen vacancies on the TiO2 surface by single-site Sn, which leads to efficient, selective activation of the nitro group coupled with a reaction involving hydrogen atoms activated on metal nanoparticles., Understanding of the structures and roles of catalyst promoters markedly lags behind the understanding of the structures and roles of catalytic sites. Here, the authors address this challenge by incorporating a single-site promoter—tin—on a TiO2 surface to enhance the catalytic activity of various metals on the TiO2 in selective hydrogenation of nitroarenes.

The rational design and synthesis of anisotropic 3D nanostructures with specific composition, morphology, surface structure, and crystal phase is of significant importance for their diverse applications. Here, the synthesis of well‐crystalline lotus‐thalamus‐shaped Pt‐Ni anisotropic superstructures (ASs) via a facile one‐pot solvothermal method is reported. The Pt‐Ni ASs with Pt‐rich surface are composed of one Ni‐rich “core” with face‐centered cubic (fcc) phase, Ni‐rich “arms” with hexagonal close‐packed phase protruding from the core, and facet‐selectively grown Pt‐rich “lotus seeds” with fcc phase on the end surfaces of the “arms.” Impressively, these unique Pt‐Ni ASs exhibit superior electrocatalytic activity and stability toward the hydrogen evolution reaction under alkaline conditions compared to commercial Pt/C and previously reported electrocatalysts. The obtained overpotential is as low as 27.7 mV at current density of 10 mA cm−2, and the turnover frequency reaches 18.63 H2 s−1 at the overpotential of 50 mV. This work provides a new strategy for the synthesis of highly anisotropic superstructures with a spatial heterogeneity to boost their promising application in catalytic reactions. ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Accepted version

Engineering broadband light absorbers is crucial to many applications, including energy-harvesting devices and optical interconnects. The performances of an ideal absorber are that of a black body, a dark material that absorbs radiation at all angles and polarizations. Despite advances in micrometre-thick films, the absorbers available to date are still far from an ideal black body. Here, we describe a disordered nanostructured material that shows an almost ideal black-body absorption of 98-99% between 400 and 1,400 nm that is insensitive to the angle and polarization of the incident light. The material comprises nanoparticles composed of a nanorod with a nanosphere of 30 nm diameter attached. When diluted into liquids, a small concentration of nanoparticles absorbs on average 26% more than carbon nanotubes, the darkest material available to date. By pumping a dye optical amplifier with nanosecond pulses of ∼100 mW power, we harness the structural darkness of the material and create a new type of light source, which generates monochromatic emission (∼5 nm wide) without the need for any resonance. This is achieved through the dynamics of light condensation in which all absorbed electromagnetic energy spontaneously generates single-colour energy pulses.

Piezoelectric and ferroelectric properties in the two dimensional (2D) limit are highly desired for nanoelectronic, electromechanical, and optoelectronic applications. Here we report the first experimental evidence of out-of-plane piezoelectricity and ferroelectricity in van der Waals layered ${\alpha}$-In2Se3 nano-flakes. The non-centrosymmetric R3m symmetry of the ${\alpha}$-In2Se3 samples is confirmed by scanning transmission electron microscopy, second-harmonic generation, and Raman spectroscopy measurements. Domains with opposite polarizations are visualized by piezo-response force microscopy. Single-point poling experiments suggest that the polarization is potentially switchable for ${\alpha}$-In2Se3 nano-flakes with thicknesses down to ~ 10 nm. The piezotronic effect is demonstrated in two-terminal devices, where the Schottky barrier can be modulated by the strain-induced piezopotential. Our work on polar ${\alpha}$-In2Se3, one of the model 2D piezoelectrics and ferroelectrics with simple crystal structures, shows its great potential in electronic and photonic applications., Comment: 17 pages, 5 figures, just accepted by Nano Letters

Single-atom metal catalysts offer a promising way to utilize precious noble metal elements more effectively, provided that they are catalytically active and sufficiently stable. Herein, we report a synthetic strategy for Pt single-atom catalysts with outstanding stability in several reactions under demanding conditions. The Pt atoms are firmly anchored in the internal surface of mesoporous Al2O3, likely stabilized by coordinatively unsaturated pentahedral Al3+ centres. The catalyst keeps its structural integrity and excellent performance for the selective hydrogenation of 1,3-butadiene after exposure to a reductive atmosphere at 200 °C for 24 h. Compared to commercial Pt nanoparticle catalyst on Al2O3 and control samples, this system exhibits significantly enhanced stability and performance for n-hexane hydro-reforming at 550 °C for 48 h, although agglomeration of Pt single-atoms into clusters is observed after reaction. In CO oxidation, the Pt single-atom identity was fully maintained after 60 cycles between 100 and 400 °C over a one-month period., Using precious noble elements as single atom metal catalysts is highly desirable and effective. Here the authors show the use of platinum atom catalysts anchored in mesoporous Al2O3 for selective hydrogenation and CO oxidation that have better stability and performance compared to their nanoparticle counterparts.