Observation of the Orbital Rashba-Edelstein Magnetoresistance.

We report the observation of magnetoresistance (MR) that could originate from the orbital angular momentum (OAM) transport in a permalloy (Py)/oxidized Cu (Cu^{*}) heterostructure: the orbital Rashba-Edelstein magnetoresistance. The angular dependence of the MR depends on the relative angle between the induced OAM and the magnetization in a similar fashion as the spin Hall magnetoresistance. Despite the absence of elements with large spin-orbit coupling, we find a sizable MR ratio, which is in contrast to the conventional spin Hall magnetoresistance which requires heavy elements. Through Py thickness-dependence studies, we conclude another mechanism beyond the conventional spin-based scenario is responsible for the MR observed in Py/Cu^{*} structures-originated in a sizable transport of OAM. Our findings not only suggest the current-induced torques without using any heavy elements via the OAM channel but also provide an important clue towards the microscopic understanding of the role that OAM transport can play for magnetization dynamics.

A fast and high-efficiency electrochemical exfoliation strategy towards antimonene/carbon composites for selective lubrication and sodium-ion storage applications.

Two-dimensional (2D) layered antimony (Sb) materials are of importance due to their unique physicochemical properties, and they can be easily electrochemically exfoliated from bulk Sb in Na2SO4 electrolyte solution. However, the exfoliation yield is quite low and the exfoliated products are easily oxidized to Sb2O3, which prohibits their practical engineering applications. Herein, an antimonene/carbon composite is successfully fabricated with a high exfoliation yield through electrochemical exfoliation of bulk antimony chunk in a mixed electrolyte solution consisting of Na2SO4 and ethylene glycol. When the as-fabricated antimonene/carbon composite is added into PAO6 oil, the lubrication system exhibits a selective lubrication performance when sliding against GCr15 and YG8 ball, and the antiwear enhancement can be further improved by sliding against a YG8 ball. Besides, the antimonene/carbon composite can provide reliability and enough ion corridors during the charge/discharge processes. When tested as an anodic material for sodium-ion batteries, it exhibits a large capacity of 485.0 mA h g-1 at a current density of 200 mA g-1 after 150 cycles and a remarkable rate capability (334.5 mA h g-1 at 5 A g-1).

Electrochemically Engineering Antimony Interspersed on Graphene toward Advanced Sodium-Storage Anodes.

Nanoengineering of metal anode materials shows great potential for energy storage with high capacity. Zero-dimensional nanoparticles are conducive to acquire remarkable electrochemical properties in sodium-ion batteries (SIBs) because of their enlarged surface active sites. However, it is still difficult to fulfill the requirements of practical applications in batteries owing to the deficiency of efficient and scalable preparation approaches of high-performance metal electrode materials. Herein, an electrochemical cathodic corrosion method is proposed for the tunable preparation of nanostructured antimony (Sb) by the introduction of a surfactant, which can efficiently avoid the agglomeration of Sb atom clusters generated from the Zintl compound and further stacking into bulk during the electrochemical process. Subsequently, graphene as the support and conductive matrix is uniformly interspersed by generating Sb nanoparticles (Sb/Gr). Moreover, the reversible crystalline-phase evolution of Sb ⇋ NaSb ⇋Na3Sb for Sb/Gr was studied by in situ X-ray diffraction (XRD). Benefiting from the interconnection of the conductive network, Sb/Gr anodes deliver a high capacity of 635.34 mAh g-1, a retained capacity of 507.2 mAh g-1 after 150 cycles at 0.1 C (1 C = 660 mAh g-1), and excellent rate performance with the capacities of 473.41 and 405.09 mAh g-1 at 2 and 5 C, respectively. The superior cycle stability with a capacity of 346.26 mAh g-1 is achieved after 500 cycles at 2 C. This electrochemical approach offers a new route toward developing metal anodes with designed nanostructures for high-performance SIBs.

Valley Pseudospin with a Widely Tunable Bandgap in Doped Honeycomb BN Monolayer.

Valleytronics is a promising paradigm to explore the emergent degree of freedom for charge carriers on the energy band edges. Using ab initio calculations, we reveal that the honeycomb boron nitride (h-BN) monolayer shows a pair of inequivalent valleys in the vicinities of the vertices of hexagonal Brillouin zone even without the protection of the C3 symmetry. The inequivalent valleys give rise to a 2-fold degree of freedom named the valley pseudospin. The valley pseudospin with a tunable bandgap from deep ultraviolet to far-infrared spectra can be obtained by doping h-BN monolayer with carbon atoms. For a low-concentration carbon periodically doped h-BN monolayer, the subbands with constant valley Hall conductance are predicted due to the interaction between the artificial superlattice and valleys. In addition, the valley pseudospin can be manipulated by visible light for high-concentration carbon doped h-BN monolayer. In agreement with our calculations, the circularly polarized photoluminescence spectra of the B0.92NC2.44 sample show a maximum valley-contrasting circular polarization of 40% and 70% at room temperature and 77 K, respectively. Our work demonstrates a class of valleytronic materials with a controllable bandgap.

An electrochemical investigation of rutile TiO2 microspheres anchored by nanoneedle clusters for sodium storage.

Rutile TiO2 microspheres anchored by nanoneedle clusters, as a new class of anode materials, are successfully employed for sodium-ion batteries and manifested good energy storage behavior. The initial discharge capacity of 308.8 mA h g(-1) is obtained and a high reversible capacity of 121.8 mA h g(-1) is maintained after 200 cycles at a current density of 0.1 C, exhibiting a high capacity retention of 83.1%. All these merits are not only ascribed to the rutile TiO2 crystal structure, but also thanks to the porous morphology of hundreds of nanoneedle clusters in favor of sodium diffusion and accommodating the strain during the sodiation and desodiation processes. Therefore, it is highly expected that rutile TiO2, as a feasible electrochemical sodium storage material, can be a new promising candidate as an anode for sodium-ion batteries.

The mechanistic exploration of porous activated graphene sheets-anchored SnO2 nanocrystals for application in high-performance Li-ion battery anodes.

Porous activated graphene sheets have been for the first time exploited herein as encapsulating substrates for lithium ion battery (LIB) anodes. The as-fabricated SnO2 nanocrystals-porous activated graphene sheet (AGS) composite electrode exhibits improved electrochemical performance as an anode material for LIBs, such as better cycle performance and higher rate capability in comparison with graphene sheets, activated graphene sheets, bare SnO2 and SnO2-graphene sheet composites. The superior electrochemical performances of the designed anode can be ascribed to the porous AGS substrate, which improves the electrical conductivity of the electrode, inhibits agglomeration between particles and effectively buffers the strain from the volume variation during Li(+)-intercalation-de-intercalation and provides more cross-plane diffusion channels for Li(+) ions. As a result, the designed anode exhibits an outstanding capacity of up to 610 mA h g(-1) at a current density of 100 mA g(-1) after 50 cycles and a good rate performance of 889, 747, 607, 482 and 372 mA h g(-1) at a current density of 100, 200, 500, 1000, and 2000 mA g(-1), respectively. This work is of importance for energy storage as it provides a new substrate for the design and implementation of next-generation LIBs exhibiting exceptional electrochemical performances.

Enhanced kinetic behaviors of hollow MoO2/MoS2 nanospheres for sodium-ion-based energy storage.

Mo-based heterostructures offer a new strategy to improve the electronics/ion transport and diffusion kinetics of the anode materials for sodium-ion batteries (SIBs). MoO2/MoS2 hollow nanospheres have been successfully designed via in-situ ion exchange technology with the spherical coordination compound Mo-glycerates (MoG). The structural evolution processes of pure MoO2, MoO2/MoS2, and pure MoS2 materials have been investigated, illustrating that the structureofthenanospherecan be maintained by introducing the S-Mo-S bond. Based on the high conductivity of MoO2, the layered structure of MoS2 and the synergistic effect between components, as-obtained MoO2/MoS2 hollow nanospheres display enhanced electrochemical kinetic behaviors for SIBs. The MoO2/MoS2 hollow nanospheres achieve a rate performance with 72% capacity retention at a current of 3200 mA g-1 compared to 100 mA g-1. The capacity can be restored to the initial capacity after a current returns to 100 mA g-1, while the capacity fading of pure MoS2 is up to 24%. Moreover, the MoO2/MoS2 hollow nanospheres also exhibit cycling stability, maintaining a stable capacity of 455.4 mAh g-1 after 100 cycles at a current of 100 mA g-1. In this work, the design strategy for the hollow composite structure provides insight into the preparation of energy storage materials.

Multidimensional antimony nanomaterials tailored by electrochemical engineering for advanced sodium-ion and potassium-ion batteries.

Downsizing the dimensions of materials holds great importance for promoting the alkali-ion storage properties, which is considered to be one of the most efficient methods for improving the cycling stability and rate capability of alloy anodes. Nevertheless, efficient, affordable, and scalable methods to prepare low-dimensional electrode materials are lacking. In this study, we developed a tunable electrochemical strategy for synthesizing multidimensional antimony (Sb) nanomaterials. Depending on different reaction mechanisms in different electrolytes, we fabricated zero-dimensional Sb nanoparticles, two-dimensional (2D) antimonene nanosheets, and a three-dimensional porous Sb network through the electrochemical delamination of bulk Sb in lithium hexafluorophosphate in propylene carbonate, tetraethylammonium hydroxide aqueous solution, and tetraethylammonium hexafluorophosphate in N, N-dimethylformamide, respectively. In the preferred electrolyte, 2D antimonene nanosheets deliver a large sodium storage capacity of 572.5 mAh g-1 after 200 cycles at 0.2 A g-1 and an excellent rate capability of 553.6 mAh g-1 at 5 A g-1. When used as anode materials for potassium-ion batteries, we obtained a high capacity of 550.3 mAh g-1 after 300 cycles, and observed a high rate capability of 302.3 mAh g-1 at 4 A g-1. These results provide an easy and tunable strategy for designing high-performance low-dimensional materials for next-generation batteries.

Heterogeneous Fenton degradation of ofloxacin catalyzed by magnetic nanostructured MnFe2O4 with different morphologies.

Magnetic nanostructured MnFe2O4 with different morphologies, synthesized via chemical co-precipitation and hydrothermal method, was assayed as heterogeneous Fenton catalysts. The as-prepared MnFe2O4 catalysts were thoroughly characterized by various characterization methods, such as X-ray diffraction (XRD), N2 adsorption-desorption, transmission electron microscopy (TEM), magnetic hysteresis loops, temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS). The catalytic activity of MnFe2O4 catalysts was evaluated in the heterogeneous Fenton degradation of ofloxacin (OFX). In our study, the morphology exhibited a critical impact on the catalytic activity of MnFe2O4. For example, MnFe2O4 nanorods (MnFe2O4-NR) had a higher catalytic activity than MnFe2O4 nanospheres (MnFe2O4-NS) and MnFe2O4 nanocubes (MnFe2O4-NC) in OFX removal and H2O2 decomposition. Notably, the catalytic activity was remarkably enhanced with increasing the relative amount of Mn3+ and Fe2+ species on the surface. Based on the results from quenching experiments and quantitative determination of •OH radicals, a possible catalytic mechanism of MnFe2O4 was proposed. In addition, the stability and reusability of MnFe2O4-NR was ascertained, as the results suggested that MnFe2O4-NR was a stable and easily separated catalyst for heterogeneous Fenton process.

Few-layer Bi2O2CO3 nanosheets derived from electrochemically exfoliated bismuthene for the enhanced photocatalytic degradation of ciprofloxacin antibiotic.

Few-layer two-dimensional (2D) Bi2O2CO3 nanosheets with a thickness of 4-5 nm were successfully fabricated via electrochemical exfoliation, followed by an exposure to ambient conditions. The formation process for these nanosheets was explored through ex situ X-ray diffractometer. The photocatalytic capacity of 2D Bi2O2CO3 nanosheets was investigated towards the degradation of ciprofloxacin. It was shown that 2D Bi2O2CO3 nanosheets exhibited better catalytic performance than Bi2O2CO3 nanoparticles synthesized by hydrothermal method under UV-Vis light irradiation. The enhanced photocatalytic activity is due to the larger specific surface area, as well as the lower band gap. Additionally, the radical trap experiments demonstrate that holes and hydroxyl radicals are of great importance in the degradation of ciprofloxacin. Finally, the 2D Bi2O2CO3 nanosheets show high stability in the photocatalytic degradation of ciprofloxacin, and could have a prospective application in the treatment of antibiotic wastewater.

Electrochemical exfoliation of graphene-like two-dimensional nanomaterials.

Unlike zero-dimensional quantum dots, one-dimensional nanowires/nanorods, and three-dimensional networks or even their bulk counterparts, the charge carriers in two-dimensional (2D) materials are confined along the thickness while being allowed to move along the plane. They have distinct characteristics like strong quantum confinement, tunable thickness, and high specific surface area, which makes them a promising candidate in a wide range of applications such as electronics, topological spintronic devices, energy storage, energy conversion, sensors, biomedicine, catalysis, and so on. After the discovery of the extraordinary properties of graphene, other graphene-like 2D materials have attracted a great deal of attention. Like graphene, to realize their potential applications, high efficiency and low cost industrial scale methods should be developed to produce high-quality 2D materials. The electrochemical methods usually performed under mild conditions are convenient, controllable, and suitable for mass production. In this review, we introduce the latest and most representative investigations on the fabrication of 2D monoelemental Xenes, 2D transition-metal dichalcogenides, and other important emerging 2D materials such as organic framework (MOF) nanosheets and MXenes through electrochemical exfoliation. The electrochemical exfoliation conditions of the bulk layered materials are discussed. The numerous factors which will affect the quality of the exfoliated 2D materials, the possible exfoliating mechanism and potential applications are summarized and discussed in detail. A summary of the discussion together with perspectives and challenges for the future of this emerging field is also provided in the last section.

Stability and its mechanism in Ag/CoOx/Ag interface-type resistive switching device.

Stability is an important issue for the application of resistive switching (RS) devices. In this work, the endurance and retention properties of Ag/CoOx/Ag interface-type RS device were investigated. This device exhibits rectifying I-V curve, multilevel storage states and retention decay behavior, which are all related to the Schottky barrier at the interface. The device can switch for thousands of cycles without endurance failure and shows narrow resistance distributions with relatively low fluctuation. However, both the high and low resistance states spontaneously decay to an intermediate resistance state during the retention test. This retention decay phenomenon is due to the short lifetime τ (τ = 0.5 s) of the metastable pinning effect caused by the interface states. The data analysis indicated that the pinning effect is dependent on the depth and density of the interface state energy levels, which determine the retention stability and the switching ratio, respectively. This suggests that an appropriate interface structure can improve the stability of the interface-type RS device.

Synergetic crystallization in a Nd2Fe14B/α-Fe nanocomposite under electron beam exposure conditions.

Nd2Fe14B/α-Fe nanocomposite magnets are prepared through electron beam exposure with a greatly reduced annealing time of 0.1 s. This is by far the most effective approach due to the effect of an extremely high heating rate featuring a rapid thermal process. The impact that the rapid thermal process has on crystallization is expounded by the introduction of the Landau model and Langevin dynamical simulations. The change of crystallization sequence from the α-Fe phase preceding the Nd2Fe14B phase under conventional annealing conditions, to synergetic crystallization under electron beam conditions is investigated. Synergetic crystallization results in more intense interaction between the α-Fe phase and the Nd2Fe14B phase in order to refine the microstructure as the fraction of Fe increases within our addition range. Improved uniformity, and shifts in the microstructure and distribution of the α-Fe phase contribute to the improvement of the magnetic properties. Compared with conventional furnace annealing ones, the magnetic properties of samples under electron beam exposure conditions are improved. For the Nd10Fe83.3B6.2Nb0.2Ga0.3 alloy, coercivity is enhanced from 4.56 kOe to 6.73 kOe, remanence ratio increases from 0.75 to 0.79, and a superior squareness of the hysteresis loop is achieved.

One-Dimensional Rod-Like Sb2S3-Based Anode for High-Performance Sodium-Ion Batteries.

Due to the high theoretical capacity of 946 mAh g(-1), Sb2S3 can be employed as promising electrode material for sodium-ion batteries (SIBs). Herein, the sodium storage behaviors of one-dimensional (1D) Sb2S3-based materials (Sb2S3 and Sb2S3@C rods) are successfully studied for the first time, displaying good cyclability and rate capability owing to their unique morphology and structure. Specifically, the Sb2S3@C rods electrode presents greatly enhanced electrochemical properties, resulting from the introduction of thin carbon layers which can effectively alleviate the strain caused by the large volume change and simultaneously improve the conductivity of electrode during cycling. At a current density of 100 mA g(-1), it delivers a high capacity of 699.1 mAh g(-1) after 100 cycles, which corresponds to 95.7% of the initial reversible capacity. Even at a high current density of 3200 mA g(-1), the capacity can still reach 429 mAh g(-1). This achievement may be a significant exploration for develpoing novel 1D Sb-based materials or metal sulfide SIBs anodes.

Tunable Valley Polarization and Valley Orbital Magnetic Moment Hall Effect in Honeycomb Systems with Broken Inversion Symmetry.

In this Letter, a tunable valley polarization is investigated for honeycomb systems with broken inversion symmetry such as transition-metal dichalcogenide MX2 (M = Mo, W; X = S, Se) monolayers through elliptical pumping. Compared to circular pumping, elliptical pumping is a more universal and effective method to create coherent valley polarization. When two valleys of MX2 monolayers are doped or polarized, a novel anomalous Hall effect (called valley orbital magnetic moment Hall effect) is predicted. Valley orbital magnetic moment Hall effect can generate an orbital magnetic moment current without the accompaniment of a charge current, which opens a new avenue for exploration of valleytronics and orbitronics. Valley orbital magnetic moment Hall effect is expected to overshadow spin Hall effect and is tunable under elliptical pumping.

Alternating Voltage Introduced NiCo Double Hydroxide Layered Nanoflakes for an Asymmetric Supercapacitor.

An electrochemical alternating voltage approach of producing NiCo double hydroxide (NiCoDH) layered ultrathin nanoflakes with large specific surface area (355.8 m(2) g(-1)), remarkable specific capacitance and rate capability is presented. The obtained NiCoDH as anode for asymmetric supercapacitors shows excellent energy density of 17.5 Wh kg(-1) at high power density of 10.5 kW kg(-1) and cycling stability (91.2% after 10,000 cycles).

NiSb alloy hollow nanospheres as anode materials for rechargeable lithium ion batteries.

NiSb alloy hollow nanospheres (HNSs) obtained by galvanic replacement were firstly applied as anode materials for lithium ion batteries, giving the best electrochemical performances for NiSb alloy materials so far with a high reversible capacity of 420 mA h g(-1) after 50 cycles, close to its theoretical capacity (446 mA h g(-1)).

Sodium/Lithium storage behavior of antimony hollow nanospheres for rechargeable batteries.

Sodium-ion batteries (SIBs) have come up as an alternative to lithium-ion batteries (LIBs) for large-scale applications because of abundant Na storage in the earth's crust. Antimony (Sb) hollow nanospheres (HNSs) obtained by galvanic replacement were first applied as anode materials for sodium-ion batteries and exhibited superior electrochemical performances with high reversible capacity of 622.2 mAh g(-1) at a current density of 50 mA g(-1) after 50 cycles, close to the theoretical capacity (660 mAh g(-1)); even at high current density of 1600 mA g(-1), the reversible capacities can also reach 315 mAh g(-1). The benefits of this unique structure can also be extended to LIBs, resulting in reversible capacity of 627.3 mAh g(-1) at a current density of 100 mAh g(-1) after 50 cycles, and at high current density of 1600 mA g(-1), the reversible capacity is 435.6 mAhg(-1). Thus, these benefits from the Sb HNSs are able to provide a robust architecture for SIBs and LIBs anodes.

A novel strategy to assemble colloidal gold nanoparticles at the water-air interface by the vapor of formic acid.

We report a novel strategy on the controlled assembly of gold nanoparticles (NPs) at the air-water interface by designing a concentration gradient of electrolytes utilizing volatile weak acidic electrolytes. Films of close-packed Au NPs can be facilely obtained by exposing citrate-protected gold colloids to the vapor of formic acid for several hours in an airtight desiccator at room temperature. Both the higher interfacial concentration of formic acid and the buffer effect of citrate solution play the key roles in the assembly. They engender a gradient distribution of hydrogen ions such that to trigger the interfacial assembly of gold NPs while preventing the bulk colloid from aggregation and coagulation. Comparative investigations have also been performed either using other volatile electrolytes like weaker acetic acid and stronger hydrochloric acid or adding an electrolyte directly into the colloids. The as-prepared films of gold NPs can serve as good substrates for surface-enhanced Raman scattering (SERS). This strategy has also been applied to the assembly of some other NPs like colloidal Pt at the air-water interface.