Search

Solid-state thermoelectric technology, interconverting heat to electrical energy, offers a promising solution for relaxing global energy problems. A high dimensionless figure of merit ZT is desirable for high-efficiency thermoelectric power generation. To date, thermoelectric materials research has focused on increasing the material’s ZT. Here we first fabricated phase-separated Sn1–xPbxSe materials by hydrothermal synthesis. We demonstrate that the simultaneous optimization of the power factor and significant reduction in thermal conductivity can be achieved in the phase-separated Sn1–xPbxSe material. The introduction of the PbSe phase contributes to improvement of the electrical conductivity and power factor of the SnSe phase. Meanwhile, nanoscale precipitates and mesoscale grains define all-scale hierarchical architectures to scattering phonons, leading to low lattice thermal conductivity. These two favorable factors lead to remarkably high thermoelectric performance with ZT ∼ 1.7 at 873 K in polycryst...

Here, we present a universal route for the rational design of graphene-based supercapacitor electrode. In this method, graphene oxide film (GO) deposited on Ni foam was directly reduced in a short times by light reduction process using a high-pressure Hg lamp. UV-assisted reduction of GO on Ni foam is a green, rapid and facile way while avoiding the use of toxic chemicals and help to simplify the fabrication steps of supercapacitor electrodes by comparison of traditional fabrication procedures. The photoreduction graphene (PrGO) sheets were grown on Ni foam without any conductive agents and polymer binders, and thus to form a composite structure with continuous and interconnected network, which is beneficial to greatly reduce contact resistance between PrGO sheets and metal current collector and facilitates the efficient access of electrolyte ions to the graphene surface and shorten the ion diffusion path. As applied in supercapacitors, the resulting PrGO electrode shows ideal and reversible capacitive behaviour and excellent electrochemical performance. Moreover, this strategy affords a simple and highly versatile route for fabricating graphene electrode materials for supercapacitors.

An efficient scheme was designed to selectively synthesize different categories of core/shell structured magnetic nanoparticles/carbon-based nanohybrids such as Fe3O4/C and Fe/helical carbon nanotubes (HCNTs) through the decomposition of acetylene directly over Fe2O3 nanotubes by controlling the pyrolysis temperature. The measured electromagnetic parameters indicated that the Fe/HCNT nanohybrids exhibited enhanced microwave absorption properties, which may be related to their special structures. The optimum reflection loss (RL) could reach −47.1 dB at 17.39 GHz with a matching thickness of 1.39 mm. The absorption bandwidth with the RL values below −20 dB was up to 11.59 GHz. Moreover, based on the obtained results, the possible enhanced EM absorption mechanisms were also discussed in detail. The results show excellent microwave absorption materials that are lightweight, have strong absorption and a wide absorption frequency band may be realized in these nanohybrids.

High quality MnO2/MnCo2O4 composites have been successfully synthesized by a one-step solution combustion process at 300 °C for 2 h in air. The effects of the amount of glycine and molar ratios of Mn/Co on phase composition, morphology and electrochemical properties of products were investigated. The prepared samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, transmission electron microscopy and Brunauer-Emmett-Teller methods. Based on the optimum fuel/oxidizer molar ratios, the products transformed from spinel MnCo2O4 granular aggregates to a mixture of MnO2/MnCo2O4 composites with increase the molar ratios of Mn/Co. The electrochemistry performance of prepared different specimens were evaluated and compared through cyclic voltammetry and charge-discharge anylysis in 2.0 M KOH electrolytic solution. Electrochemical measurements showed that the MnO2/MnCo2O4 exhibited a optimal electrochemistry performance with the Mn:Co:glycine molar ratio of 3:4:31.5/9. The maximum specific capacitance of 497 F/g is achieved at a current density of 0.5 A/g (or 312 F/g at 10 A/g). The high electrochemical performance would be attributed to the numerous nanopores, large specific surface and synergistic effects of the MnO2 and spinel MnCo2O4.

Here, we present a liquid–solid method (termed “LS method”) for the formation of spherical metal powders. By taking advantage of the low wettability of metal liquids on a solid powder, spherical metal droplets were formed under the influence of interfacial and surface tension, as demonstrated for copper, silver, aluminum, copper–tin alloy, copper–zinc alloy, and amorphous magnetic iron–silicon–boron materials. This LS method is a versatile and universal route and would be applied in powder metallurgy, 3D printing and metal injection modeling. We believe this method provide an additional way for the formation of spherical metal powders. Keywords: Surface energy, Interface wetting, Powder processing

A symmetrical Fe2O3/BaCO3 hexagonal cone structure having a height of 10 μm and an edge length of ~4 μm is reported, obtained using a common solvothermal process and a mirror growth process. Focused ion beam and high-resolution transmission electron microscopy techniques revealed that α-Fe2O3 was the single crystal feature present. Ba ions contributed to the formation of symmetrical structures exhibited in the final composites. Subsequently, porous magnetic symmetric hexagonal cone structures were used to study the observed intense electromagnetic wave interference. Electromagnetic absorption performance studies at 2–18 GHz indicated stronger attenuation electromagnetic wave ability as compared to other shapes such as spindles, spheres, cubes, and rods. The maximum absorption frequency bandwidth was at 7.2 GHz with a coating thickness d = 1.5 mm. Special structures and the absence of BaCO3 likely played a vital role in the excellent electromagnetic absorption properties described in this research.

Nitrogen-doped graphene deposited on nickel foam was prepared via a simple hydrothermal process using urea as the reducing agent and nitrogen source and was directly applied as a binder-free supercapacitor electrode. The N content was 5.01 at. %. The electrochemical test of the prepared N-doped graphene showed ideal and reversible capacitive behaviour and excellent electrochemical performance, with a high specific capacitance of 223 F g−1 at 0.29 A g−1, a high-rate capability with the specific capacitances maintained at 184 F g−1 at a high rate of 35.7 A g−1, and good cycling stability with the specific capacitance of the N-doped graphene increased to 206 F g−1 after 3000 cycles. The results suggest its promising application as an electrode material for supercapacitor.

We report a detailed investigation of the thermopower and magnetic properties of La 0.95 Ba 0.05 CoO 3 . The large negative magnetothermopower is found to scale with both magnetic field and temperature, indicating a spin-entropy contribution to the thermpower. We formulate a new general expression to describe the thermopower from spin entropy with spin-interaction considered. The scaling behaviour is analyzed in a theoretical model, which provides a satisfactory description of the observed data. The magnetic results further support our analysis. This investigation shows that spin entropy plays a substantial role in the thermopower.

Here, porous grapheme oxide (GO) gel deposited on nickel foam was prepared by using polystyrene (PS) colloidal particles as spacers for use as electrodes in high rate supercapacitors, then reduced by Vitamin C aqueous solution in ambient condition. The PS particles were surrounded by reduced graphene oxide (rGO) sheets, forming crinkles and rough textures. When PS particles were selectively removed, rGO gel coated on the skeleton of Ni foam can formed an open porous structure, which prevents elf-aggregation and restacking of graphene sheets. The porous rGO-based supercapacitors exhibit excellent electrochemical performances such as a specific capacitance of 152 F g−1 at 1 A g−1, high rate capability of 53% capacitance retention upon a current increase to 100 A g−1 and good cycle stability, due to effective rapid and short pathways for ionic and electronic transport provided by the sub-micrometer structure of rGO gel and 3D interconnected network of Ni foam.

Over water-soluble alkali carbonate particles, coiled carbon nanofibers were produced in large quantities through the pyrolysis of acetylene at 450 °C. By controlling the component of catalyst, coiled carbon nanofibers and carbon nanofibers could be synthesized selectively. And the pyrolysis temperature also had a great impact on the yield and morphology of the obtained samples. By regulating the temperature, carbon nanofibers, carbon nanotubes and bamboo-like carbon nanotubes could be synthesized, respectively. Because the used catalysts were water-soluble alkali salts, the purification was very mild and high purity of carbon nanomaterials could be obtained expediently through a simple water washing process. The photoluminescence investigation indicated that the obtained samples exhibited a blue and two ultraviolet peaks, and the photoluminescence intensity could be enhanced greatly by increasing the excited wavelength. Therefore, the proposed route for the growth and purification of carbon nanomaterials is simple, environmentally friendly and low-cost.

Nd0.5Sr0.5MnO3 nanoparticles with average sizes of 32-1000 nm in diameter were prepared by sol-gel method. The synthesized nanoparticles were characterized using X-ray diffraction, high- resolution transmission microscopy, scanning electron microscopy, and vibrating sample magnetometer. All samples have the single-phase orthorhombic structure, and the grain size increases with the increase in annealing temperature. A charge ordering (CO) transition at T(CO) and a ferromagnetic-paramagnetic transition at Tc were observed in 1000 nm nanoparticles. With the decrease in particle size, CO transition gradually shifts to lower temperature, becomes increasingly weak, and disappears for 85 nm nanoparticles. An inverse magnetocaloric effect with positive magnetic entropy change was observed around T(CO), and it decreases with the decrease in size due to the suppression of CO phase. The observed negative magnetic entropy change at Tc shows a surprising nonmonotonic behavior with the variation of particles size. All these results may give rise to a new insight into the magnetothermal behaviors in nanosized CO perovskite manganites.

Our previous studies showed that extremely low frequency magnetic fields (ELF-MFs) inhibited tumor growth and change proportion of splenic regulatory T cells (Treg cells). Here, we focus on the effect of ELF-MFs on lung metastatic melanoma mouse model and the regulatory mechanism of ELF-MFs on the differentiation of Treg cells. Tumor-bearing mice were exposed to sham ELF-MFs and ELF-MFs (0.4 T, 7.5 Hz) 2 h/day for 27 days. Metastatic tumor burden of lung was significantly decreased after ELF-MF treatment. Compared to the control group, expressions of matrix metalloproteinase (MMP2, MMP9) and forkhead box P3 (Foxp3) in lung nodules significantly decreased in the ELF-MF group. Moreover, in vitro, after stimulated with anti-CD3, anti-CD28 antibodies and transforming growth factor-β (TGF-β) and treated with ELF-MFs for 2 h, expression of Foxp3 in total T cells was significantly decreased. Differentiation rate of Treg cells was inhibited from 32.0% to 22.1% by ELF-MFs. Furthermore, reactive oxygen species (ROS) was increased and phospho-serine/threonine protein kinase (p-AKT) was inhibited in both T cells and Jurkat cells. ROS scavenger N-acetyl-l-cysteine reversed inhibition of AKT pathway and expression of Foxp3 from 18.6% to 26.6% in T cells. Taken together, our data show that ELF-MF exposure promoted the inhibitory effect of ROS on AKT pathway and decreased Foxp3 expression, which provides an explanation for why ELF-MF exposure can inhibit differentiation of Treg cells and enhance antitumor effect in metastatic melanoma mouse model.

Spherical Fe-based magnetic powders were obtained by taking advantage of the surface tension of a molten metal and the de-wetting of metal droplets on a solid graphite sea. The surface carbides inhibit the interfacial reaction and suppress the wetting of the alloy in the graphite substrate. Cross-sectional micrographs of the spherical particles indicate that the particles are fully dense without pores and bulk inclusions. The amorphous degree of the spherical powder was improved by directly quenching in water compared to the raw materials, and the directly quenched sample exhibits excellent soft magnetic properties. Our strategy is expected to provide a new route for the fabrication of spherical insulation coated Fe-based magnetic powders for use in high frequency devices as magnetic core powders.

To overcome the shortcomings (poor impedance mismatching and weak electromagnetic wave attenuation) of the Co nanoparticles embedded into nanoporous carbon (Co@NPC) derived from the thermal decomposition of zeolitic imidazolate framework-67 (ZIF-67), two coated titanium oxide (TiO2) routes are designed to prepare core–shell Co@NPC@TiO2 and multi-interfaced yolk–shell C–ZIF-67@TiO2 (obtained from the thermal decomposition of ZIF-67@TiO2) structures. The permittivity and permeability of C–ZIF-67@TiO2 significantly depend on the thickness of the TiO2 shell in ZIF-67@TiO2, and the thickness of the TiO2 shell in the as-obtained samples can be easily controlled via changing the addition content of tetrabutyl titanate in the hydrolyzation process. The as-prepared samples have remarkable absorbing characteristics in wide frequency bands from 2–18 GHz with thicknesses of 1.0–5.0 mm. 50 wt% of the C–ZIF-67@TiO2-2 (the addition amount of tetrabutyl titanate is 2 mL) nanocomposite filled within paraffin shows a maximum reflection loss (RL) of −51.7 dB at an absorbing thickness of 1.65 mm, meanwhile, for the Co@NPC@TiO2-1.2 (the addition amount of tetrabutyl titanate is 1.2 mL) nanocomposite, a maximum RL can be achieved of −31.7 dB at 1.5 mm. This study provides a good reference for the future preparation of other carbon-based lightweight microwave absorbing materials derived from metal organic frameworks.

Self-assembly of nanoparticles is one of the most appealing fields in nanoscience. In the present article, we demonstrate solvent-directed and anion-modulated self-assemblies of ZnO recrystallized from layered basic zinc acetate nanoflakes by heat treatment in liquid media. Diverse controllable ZnO patterns, including nanodots, nanodisks, twinned mesocrystals, mesoporous nanospheres, unprecedented triangular nanoprisms and porous nanosheets, have been achieved from the same precursor, indicating a fascinating platform for studies of self-assembly. It is confirmed that polar protic solvents such as water, alcohol and methanol not only provide liquid media to disperse the precursor nanoflakes but also force their decomposition under mild conditions without basic additives and direct self-assemblies of the resulting ZnO. Both the physicochemical property and the structure of the solvent play important roles. Due to the anion exchange reactions of zinc hydroxide salts and face-selective electrostatic interactions between the added anions and wurtzite ZnO, the conversion and self-assembly process can be effectively modulated by the addition of anions. When the affinity of added anions to the zinc hydroxide layers is weak, the conversion process will be slackened and the preferential assembly direction of ZnO will be modified. However, when the affinity is strong, other stable zinc hydroxide salts instead of ZnO will be obtained. Our findings give new insights into the solid-phase transformation and assembly from the precursor nanoflakes to ZnO. In addition, the outstanding light scattering feature of the resulting ZnO mesocrystals confers application significance on them.

We have studied Ru-doping effect on the thermopower and electrical transport properties of Ca3Co4O9+δ samples. A thermopower in Ca3Co4−xRuxO9+δ was enhanced by Ru doping. A clear field-induced suppression of thermopower implies a large spin entropy contribution. Magnetic results indicate that the spin entropy enhancement originates from the decrease of Co4+ concentration induced by Ru-doping. The increase of resistivity results from the decreases of carrier concentration and mobility. The electrical transport properties reveal that Ru-doping induces a metal–insulator transition at x≈0.2 and the thermally activated mechanism dominates the transport behavior at low temperature.

An effective multi-exfoliation method based on lithium (Li) intercalation has been demonstrated for preparing monolayer molybdenum disulfide (MoS2) quantum dots (QDs). The cutting mechanism of MoS2 QDs may involve the complete breakup around the defects and edges during the reaction of LixMoS2 with water and its following ultrasonication process. The multiply exfoliation make the MoS2 fragile and easier to break up. After the third exfoliation, a large number of monolayer MoS2 QDs is formed. The as-prepared MoS2 QDs show photoluminescence (PL) inactive due to the existence of 1T phase. After heating treatment, the PL intensity excited at 300 nm is enhanced by five times. The MoS2 QDs solution has an excitation-dependent luminescence emission which shifts to longer wavelengths when the excitation wavelength changes from 280 nm to 370 nm. The optical properties are explored based on the quantum confinement and edge effect.

Spherical Cu–Zn alloy powders were fabricated by combining the surface tension of a molten metal with the de-wetting of a metal droplet on a graphite surface. The effect that the gas pressure had on the surface morphology and composition was studied. The Zn concentration can be maintained at 20.18 wt.%, 15.5 wt.% and 12.08 wt.% using 0.22 MPa, 0.10 MPa, and 0.04 MPa, respectively, from a commercially available Cu–38 wt.%Zn raw material. The gas pressure was adjusted to control the surface volatility of Zn without affecting the spherical morphology, and higher gas pressure yielded less volatile Zn. The Cu–Zn alloy powders were perfectly spherical, even at a negative pressure of 0.04 MPa. The spherical Cu–Zn alloy particles hardly changed and were fully dense up to Cu–50 wt.%Zn, which allowed high-quality spherical Cu–Zn alloy powders to potentially serve a large composition range.

Spin Hall nano oscillator (SHNO), a new type spintronic nano-device, can electrically excite and control spin waves in both nanoscale magnetic metals and insulators with low damping by the spin current due to spin Hall effect and interfacial Rashba effect. Several spin-wave modes have been excited successfully and investigated substantially in SHNOs based on dozens of different ferromagnetic/nonmagnetic (FM/NM) bilayer systems (e.g., FM = Py, [Co/Ni], Fe, CoFeB, Y3Fe5O12; NM = Pt, Ta, W). Here, we will review recent progress about spin-wave excitation and experimental parameters dependent dynamics in SHNOs. The nanogap SHNOs with in-plane magnetization exhibit a nonlinear self-localized bullet soliton localized at the center of the gap between the electrodes and a secondary high-frequency mode which coexists with the primary bullet mode at higher currents. While in the nanogap SHNOs with out of plane magnetization, besides both nonlinear bullet soliton and propagating spin-wave mode are achieved and controlled by varying the external magnetic field and current, the magnetic bubble skyrmion mode also can be excited at a low in-plane magnetic field. These spin-wave modes show thermal-induced mode hopping behavior at high temperature due to the coupling between the modes mediated by thermal magnon mediated scattering. Moreover, thanks to the perpendicular magnetic anisotropy induced effective field, the single coherent mode also can be achieved without applying an external magnetic field. The strong nonlinear effect of spin waves makes SHNOs easy to achieve synchronization with external microwave signals or mutual synchronization between multiple oscillators which improve the coherence and power of oscillation modes significantly. Spin waves in SHNOs with an external free magnetic layer have a wide range of applications from as a nanoscale signal source of low power consumption magnonic devices to spin-based neuromorphic computing systems in the field of artificial intelligence.

We report a perpendicular magnetic tunnel junction (pMTJ) cell with a tunnel magnetoresistance (TMR) ratio of nearly 200% at room temperature based on CoFeB/Ta/CoFeB as the free layer (FL) and a synthetic antiferromagnetic (SAF) multilayer [Pt/Co]/Ru/[Pt/Co]/Ta/CoFeB as the reference layer (RL). The field-driven magnetization switching measurements show that the pMTJs exhibit an anomalous TMR hysteresis loop. The spin-polarized layer CoFeB of SAF-RL has a lower critical switching field than that of FL. The reason is related to the interlayer exchange coupling (IEC) through a moderately thick Ta spacer layer among SAF-RLs, which generates a moderate and negative bias magnetic field on CoFeB of RL. However, the IEC among RLs has a negligible influence on the current-driven magnetization switching of FL and its magnetization dynamics.

Nanoscale refractive index (RI) sensors based on plasmonic structures usually suffer from a low figure of merit (FoM) due to the broad linewidth of the resonance peaks. Here, we report a magnetoplasmon-based RI sensing method with high FoM in the designed H-shaped magnetoplasmonic crystals. Instead of the light intensity spectrum, the Faraday signal is detected to analyze the changes of the surrounding RI. Sharp resonance with extremely narrow linewidth is obtained by plotting the reciprocal Faraday rotation near the null point region. Therefore, the FoM is hugely enhanced, and a theoretical value exceeding 1775/RIU is achieved, which is one order of magnitude higher than has ever been reported, to the best of our knowledge, for the RI sensor based on the Faraday effect. The Faraday reversal and the enhanced FoM arise from the Fano resonance. These findings are of potential value for practical high performance biochemical sensors.

Ultrathin 2D carbon nitride sheets (CNs) are potential materials for solar energy conversion. However, these ultrathin sheets usually suffer from a wider bandgap of 3.06 eV, and thus nothing but ultraviolet range absorption. Here, we realized that red CNs has a narrower bandgap of 2.05 eV with a strong band-to-band visible-light absorption band by fluorination of atomic CNs followed by thermal defluorination (F-DF). Theoretical calculation results indicate that (i) a defect band arises near the conduction band minimum (CBM) after F-DF, resulting in a downward shift of the CBM, and (ii) the band structures are highly associated with the spatial distribution of defects in ultrathin 2D CNs. Furthermore, we confirm that such visible-light absorption band of red CNs can enable the number of photons to harvest a larger portion of solar spectrum, and suppress the rapid recombination of the photogenerated carriers. Consequently, the red CNs-sensitized TiO2 nanorod-based photoanode exhibits an outstanding photoelectrochemical water splitting activity in the visible light range. This work presents a new strategy for using 2D wide-bandgap material of bandgap narrowed to achieve a strong band-to-band visible-light absorption band.

To develop a high efficiency non-precious electrocatalyst with cost-effective and good stability for Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) still remains a formidable challenge. Herein, we present a new hydrothermal method based on integrating NiCo-Layered Double Hydroxides (NiCo-LDHs) with Molybdenum Sulfide (MoS2) to develop a three-dimensional (3D) MoS2/NiCo2S4 nanostructure supported on Nickel Foam (NF). To optimize the interfacial structure and promote the catalytic activity, the molar ratio of MoS2/NiCo2S4 is used to regulate the hybrids' nanostructure. The optimal MoS2/NiCo2S4/NF is obtained as the molar ratio reaches 20%, which can be used as a bifunctional electrocatalyst with ultrahigh electrocatalytic property for HER and OER in alkaline electrolyte. As expected, the optimize MoS2/NiCo2S4/NF shows an overpotential as small as 90 and 220 mV at 10 mA cm−2 for HER and OER in 1 M KOH. Additionally, an electrolyzer is assembled where MoS2/NiCo2S4/NF serves as anode and cathode electrode, the current densities achieve 10 mA cm−2 only need a cell potential of 1.49 V. This works can provide a new window for designing high-efficiency and cost-effective non-precious bifunctional catalysts based on LDHs as precursors for HER and OER in the future.

Structurally ordered Pt3Co/C nanoparticles (NPs) were obtained via a spray paint drying method with an annealing treatment. The addition of a suitable dose of polyvinylpyrrolidone resulted in a narrow size distribution of the Pt3Co/C-600-1 NPs, an average particle size of ca. 4.6 nm, which may be due to the enhanced dispersion in aqueous solution resulting from the carbon support. The sample denoted as Pt3Co/C-600-1 NPs performs high activity for oxygen reduction reaction with the mass activity (MA) ca. 3 times higher than that of a commercial Pt/C catalyst at 0.9 V. Accelerated durability tests (ADTs) showed that Pt3Co/C-600-1 NPs exhibit superior stability with a minimal loss of 17.5% in MA at 0.9 V after 5000 cycles, while Pt/C catalysts show loss of 44.4%. This simple two-step strategy provides an effective way to prepare Pt-based catalysts for industrial application.

Magnonic devices based on spin waves are considered as a new generation of energy-efficient and high-speed devices for storage and processing of information. Here we experimentally demonstrate that three distinct dominated magneto-dynamic modes are excited simultaneously and coexist in a transversely magnetized ferromagnetic wire by the ferromagnetic resonance (FMR) technique. Besides the uniform FMR mode, the spin-wave well mode, the backward volume magnetostatic spin-wave mode, and the perpendicular standing spin-wave mode are experimentally observed and further confirmed with more detailed spatial profiles by micromagnetic simulation. Furthermore, our experimental approach can also access and reveal damping coefficients of these spin-wave modes, which provides essential information for development of magnonic devices in the future.

Graphitic carbon nitride (g-CN) as a two-dimensional photocatalyst has received considerable attention. Tri-s-triazine-based crystalline carbon nitride nanosheets (CCN-nanosheets) with a thickness from 2 to 5 nm have been synthesized by a thermal procedure. The number of amino groups in the as-obtained samples significantly decreases compared with the samples before treatment (bulk-CCN), which optimizes the grain boundaries and narrows the band gap. Meanwhile, density functional theory (DFT) calculation demonstrates the distinct adjustment for the electronic structure of the sample from deamination. Combining the characteristics of two-dimensional morphology with high crystallinity, CCN-nanosheets demonstrates a high specific surface area of 154.2 m2 g−1, a suitable conductive band potential, improved photo-generated electron-hole pairs separation rate and high carrier transport efficiency. As a consequence, CCN-nanosheets exhibits an outstanding hydrogen evolution rate of 203 μmol h−1 (18 times higher than that of bulk-CCN and 20 times than that of pristine g-CN) and excellent cycling stability. It is anticipated that this facile and effective strategy for tailoring nanostructure and grain boundary would open up a new way for improving the photocatalytic performance of g-CN.

The development of bifunctional electrochemical active heterostructures for both hydrogen evolution reaction (HER) and supercapacitors provides the possibility to integrate energy conversion and storage into one single system. In this article, we have designed and investigated three-dimensional (3D) hybrid CoNiO2/CoO composites through simple hydrothermal and annealing processes, in which CoNiO2 nanowires layered on CoO nanowires arrays with distinctive hierarchically nanowires structure were supported on nickel foam. Specifically, the CoNiO2/CoO-140-400 composite (optimum experimental conditions: hydrothermal temperature 140 °C, annealing temperature 400 °C) can efficiently catalyse the HER in an alkaline electrolyte with a small overpotential of 70 mV at 10 mA cm−2 current density, and exhibit a beneficial kinetics and excellent long-term stability of 15 h without obvious fluctuations. Moreover, the material shows an areal capacitance of 5.37 F cm−2 at a current density of 1 mA cm−2, remarkable rate capability (83.9% capacity retention at 20 mA cm−2) and cycle stability (82.9% retention after 5000 cycles) for supercapacitor. This work reveals that the synergistic effects between CoNiO2 and CoO in CoNiO2/CoO-140-400 heterostructures are powerful for electrochemical property and provide a strategy to explore low cost and highly efficient electrocatalysts for the energy conversion and storage applications.

Flakey FeSiAl/ferrite composites were prepared via ball milling-assisted co-precipitation to evaluate the microstructure, morphology, and microwave absorption. Measurement of the electromagnetic properties indicated that the permittivity and permeability of flakey FeSiAl composites can be well tuned by adjusting the amount of Ni-Zn ferrite loads. We found an extraordinary tunable dielectric-type loss that enhanced microwave absorption due to the interface between FeSiAl and ferrites. This enhanced microwave absorption of flakey FeSiAl composites is derived from the synergy of metal-ferrite interface and dielectric matching. Controlled by ferrite loads of 8 wt% content, enhanced microwave absorption is achieved with the reflection loss −29.2 dB and bandwidth 4 GHz at matching thickness 2.5 mm. Furthermore, the extraordinary tunable dielectric-type loss is thickness-independent. This promising result revealed a great opportunity for flakey FeSiAl/ferrite composites in microwave absorption applications.

Atomically thin 2D carbon nitride sheets (CNs) can improve the photocatalytic performance due to their high specific surface area, exposed active sites, and nano-scaled diffusion path of the charge transferred to surface. However, in practical application, 2D CNs photocatalysts always suffer the low solar absorption. Here, we present a novel approach to achieve the ultrathin 2D CNs photocatalysts with wide spectrum absorption in visible-light range. The new method, i.e. thermal annealing of atomically thin CNs in Se vapor, can dramatically extend the absorption edge of the ultrathin CNs from 418 to 574 nm. Using structural characterization and spin-polarized density functional theory, we identify the loss of the nitrogen atoms at the edges and in situ Se doping into the network of ultrathin CNs, which could change the electronic band structure of the 2D CNs. As a consequence, the ultrathin 2D CNs photocatalyst via Se vapor annealing (Se-CNs) modified by Pt cocatalyst shows a superior photocatalytic hydrogen evolution activity under visible light irradiation. More significantly, the ultrathin Se-CNs photocatalyst also exhibits an impressive photocatalytic hydrogen evolution activity under visible-light irradiation in the absence of Pt cocatalyst. We believe that our study provide a facile and environmentally friendly strategy to realize the utilization of 2D CNs photocatalyst under wide spectrum range of solar radiation to harvest solar energy efficiently, and it can be further applied in various advanced fields, including CO2 photoreduction, organic photosynthesis, and pollutant controls.

We studied the magnetic properties of polycrystalline Y3Fe5O12 (YIG) thin films (less than 100 nm) deposited on thermally oxidized silicon wafer by magnetron sputtering and followed by the post-annealing process. Our ferromagnetic resonance (FMR) results demonstrate that sputtering at room temperature combined with the post-annealing treatment can be an efficient method to achieve large-area (inch scale) and highly uniform YIG thin films with a low damping constant α ∼ 7 × 10−3 on cheap oxidized Si wafer. Furthermore, our spin pumping experiments demonstrate that the polycrystalline YIG/Pt system has a good spin mixing conductance, where spin current can be effectively injected into the adjacent Pt layer from YIG through the interface. Then the electrical detection of magnetic properties (e.g., spin waves) of insulating YIG film can be achieved via the inverse spin Hall effect of Pt. The electrical detection of spin waves in the large-area polycrystalline YIG/Pt on silicon wafer may help to develop new spintronic devices (e.g., magnon-based devices) by utilizing the complementary metal-oxide-semiconductor (CMOS) technology.

Synthetic customized heterostructure via optimizing structure as well as designing components is considered as an effective strategy to endow materials with specific functional applications. Here, we reported a facile and green process to obtain one dimensional (1D) Fe3N@C heterogeneous structures by using organic amines as nitrogen and carbon sources. Multiple processes including nitridation, formation of Fe3N nanoparticles and encapsulation of the produced Fe3N nanoparticles are simultaneously achieved. It is well known that microwave absorbers with stability and excellent performance are very important for the practical application. In this work, the as-prepared Fe3N@C composites can maintain excellent microwave absorbing performance when the samples are exposed to the open air for 3 months. Wide effective absorption bandwidths and strong absorption can be gained with the thickness less than 2 mm. In particular, an effective absorption bandwidth as wide as 5.92 GHz was obtained with thickness of 1.8 mm. Furthermore, the vector network analyzer (VNA) tests after 9 months of exposure to air provide more favorable evidence for its excellent and stable absorbing properties. The strong stability should be attributed to the covalent bonds after nitriding and the air-barrier provided by the outer carbon base. This study may provide new insights into the design and development of high-performance electromagnetic wave absorbers with excellent stability.

are promising candidates for the permanent magnets since they can show ferromagnetism and large anisotropy by substituting Mg for Ce in a paramagnetic compound. In this work, a room-temperature ferromagnetism with a second-order magnetic phase transition is observed in the (CMC) compound prepared by a cold crucible levitation melting method. Based on the DC magnetization data, the critical phenomenon around the phase transition point ( ) in CMC is investigated and the critical exponents for spontaneous magnetization, for susceptibility and for critical isothermal magnetization are determined independently by three different data processing techniques including the modified Arrott plot, Kouvel-Fisher plot, and critical isotherm analysis. It is noteworthy that the magnetizations obey the scaling equation, indicating that the critical parameters including T c , , and are reliable and self-consistent. The calculation of spin interaction with the obtained critical exponents further suggests a long-range ferromagnetic coupling with in CMC.

Lots of work has been done to develop microwave absorbing materials (MAM) utilized as flexible electronic devices and communication instruments. Conventionally developed powder MAM are often limited in practical applications because of the bad stability and poor durability, which is out of the scope for exploiting flexible and long-term microwave absorbers. To overcome such limitations, a facile and binder-free technique from a Co-based zeolitic imidazolate framework (ZIF-67, a member of metal-organic frameworks)-coated carbon fiber precursor is developed for the in situ horizontal growth of Co3O4 nanoparticles, which embedded nitrogen-doped carbon array (triangular nanoplates) on the surface of carbon fibers in the carbon paper (NC-Co3O4/CP) as low-thickness MAM. The maximum reflection loss (RL) values reaches -16.12 and -34.34 dB when the thickness is 1.1 and 1.5 mm, respectively. As the thickness increases, the absorbing performance at low frequency performs well (RL < -20 dB). The hierarchical architecture is facilely originated from a metal-organic framework precursor. In view of the simple preparation technique, NC-Co3O4/CP exhibit huge potential in large-scale production of portable microwave absorbing electronic devices with strong microwave response at low thickness.

The sizeable direct bandgap, high mobility, and long spin lifetimes at room temperature offer black phosphorus (BP) potential applications in spin-based semiconductor devices. Toward these applications, a critical step is creating a magnetic response in BP, which is arousing much interest. It is reported here that ambient degradation of BP, which is immediate and inevitable and greatly changes the semiconducting properties, creates magnetic moments, and any degree of degradation leads to notable paramagnetism. Its Landau factor g measured is ≈1.995, revealing that the magnetization mainly results from spin rather than orbital moments. Such magnetism most likely results from the unsaturated phosphorus in the vacancies which are stabilized by O adatoms. It can be tuned by changing any one of the ambient factors of ambient temperature, humidity, and light intensity, and can be stabilized by exposing BP in argon. The findings highlight the importance of evaluating the effect of ambient degradation-induced magnetism on BP's spin-based devices. The work seems an essential milestone toward the forthcoming research upsurge on BP's magnetism.

The development of noble-metal-free highly efficient oxygen evolution reaction (OER) catalysts is crucial for electrochemical energy technology but still challenging. Herein, ultrafine cobalt–iron bimetallic phosphide nanoparticles embedded in carbon nanosheets are synthesized using two-dimensional (2D) metal–organic frameworks (MOFs) as the precursor. The 2D morphology of the carbon matrix and the ultrafine character of Co1−xFexP nanoparticles make contributions to OER catalysis. By optimizing the molar ratio of Co/Fe atoms in MOFs, a series of Co1−xFexP/C catalysts are prepared. Among them, Co0.7Fe0.3P/C shows the best OER performance with an overpotential of 270 mV at a current density of 10 mA cm−2 and an ultralow Tafel slope of 27 mV dec−1 in an alkaline electrolyte. Moderate iron doping preserves the catalytically active sites and improves the ability to be oxidized of the surface of Co1−xFexP nanoparticles, and thus enhances the OER activity. Our finding paves the way to the rational design of the morphology and chemical composition of OER catalysts.

The sensing performance of one-dimensional magnetic nanograting based on magnetoplasmons was investigated. The predictable Kerr reversal and enhancement are achieved in our experiment. The further result shows that the shift of the Kerr null point has a linear relationship with the surrounding refractive index in a wide range. In addition, a huge figure of merit (FoM) of 1728/refractive index unit is achieved, which is 1 order of magnitude higher than the results reported. The experiment and theory confirm that the excitation of surface plasmons leads to the Kerr reversal and enhancement, resulting in a huge FoM.

The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) properties of double perovskite catalysts La2CoMnO6−δ and La2NiMnO6−δ have been investigated. The experimental results demonstrate that these samples are efficient OER and ORR catalysts. For the La2CoMnO6 compound annealed at 600 °C, its half-wave potential of ORR in alkaline media is as low as 0.75 V versus reversible hydrogen electrode. As for the correlation between electrocatalytic activities and the eg orbital occupation numbers, it is found that the eg-filling rule proposed by Shao-Horn and co-workers is valid in La2CoMnO6−δ when the eg electrons of two kinds of transition-metal ions are all considered. In the case of La2NiMnO6−δ, because the samples which prepared in different conditions all have unity average eg occupation, the eg-filling rule should be amended. We suggest that the average deviation from unity eg occupation is a suitable activity descriptor, which can be used to design perovskite catalysts with unity average e...

To obtain high-performance spintronic devices with high integration density, two-dimensional (2D) half-metallic materials are highly desired. Herein, we proposed a stable 2D material, i.e., the Mg3C2 monolayer, with a honeycomb-kagome lattice based on the particle-swarm optimization algorithm and first-principles calculations. This monolayer is an anti-ferromagnetic (AFM) semiconductor in its ground state. We have also demonstrated that a transition from an AFM semiconductor to a ferromagnetic half-metal in this 2D material can be induced by carrier (electron or hole) doping. The half-metallicity arises from the 2pz orbitals of the carbon (C) atoms for the electron-doped system and from the C 2px and 2py orbitals in the case of hole doping. Our findings highlight a new promising material with controllable magnetic and electronic properties towards 2D spintronic applications.

Graphdiyne (GDY), a two-dimensional artificial-synthesis carbon material, has aroused tremendous interest because of its unique physical properties. The very high activity affords the possibility to chemically dope GDY with metal atoms or lightweight elements such as hydrogen and halogen and so on. Chemical doping has been confirmed to be an effective method to lead to various GDY derivatives with useful physical properties. Thus, this review is intended to provide an overview of the electronic, optical, and magnetic properties of pristine GDY and its derivatives reported from theories to experiments. Because of the importance of pristine GDY and its derivatives in real applications, we also summarize the main physical applications of GDY and its derivatives reported in recent years in this review. We believe that the review will be valuable to all those interested in GDY.

Special electric and magnetic characteristics make Fe

The limited operating temperature is the main obstacle for the practical applications of magnetic refrigeration. In this work, the voltage control of magnetocaloric effect (MCE) is investigated in a La0.7Sr0.3MnO3 (LSMO)/CeO2/Pt device. Different from the conventional method of volatile manipulating MCE by large-voltage-induced strain, nonvolatile manipulation of magnetocaloric operating temperature with good stability is realized in the LSMO film by applying low voltages of less than 2.3 V. The experimental results demonstrate that the magnetic entropy change peak temperature for the LSMO film can be extended from 302 to 312 K by voltage. This nonvolatile effect can be well-understood with the resistive switching mechanism and has potential in promoting microscale refrigeration technology.

In this study, we report a porous-carbon-based Mo2C nanocomposite (NCs) as the microwave absorber via typical carbothermal reduction using metal-organic frameworks (MOFs) and polyoxometalates (POMs) as the precursors, which have been rarely applied in electromagnetic (EM) wave absorption areas. The elaborately designed NCs not only bring about good impedance matching, but also possess strong dissipation ability due to the large surface areas and porous features. Thanks to the material characteristics as well as structural advantages, the as-prepared Mo2C/C NCs with 20 wt% sample loading exhibit remarkable microwave absorbing performance. The minimum RL value reaches -49.19 dB at matching thickness of 2.6 mm, and the best effective bandwidth (RL-10 dB) of 4.56 GHz at 1.70 mm was also achieved. Moreover, the NCs overcome the intrinsic drawback of traditional carbon materials, that is, centralized effective absorption always occurred at high frequency (10 GHz) and the minimum RL value of the NCs shifted to 9.04 GHz. Clearly, in this study, we not only developed the Mo2C NC as the new light absorber, but also paved the way to synthesize other available transition metal carbides using MOFs and POMs.