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Polymer composites receive attentions for protecting from electromagnetic (EM) pollution. However, their EM wave (EMW) attenuation mechanism primarily results from reflection rather than absorption. Herein, we prepared poly(vinylidene fluoride)/cobalt (Co)/MXene composite foams that exhibited applicable impedance matching, enhanced EMW absorption and high-performance thermal conduction properties. With CO2-assisted foaming, a uniform foam structure was integrated into the polymer composites, and meanwhile, the introduced MXenes were partially oxidized and transformed into TiO2 and amorphous carbon. The formed TiO2 not only provided extra heterogeneous interfaces and capacitor-like structures in favor of dielectric polarization but also reduced the excessive electrical conductivity of the pristine MXenes to favor impedance matching. Accordingly, the EMW absorbing performance of the composite foam was enhanced with a minimum reflection loss of −45.6 dB at 4 mm when the filler content was only 12 wt% (6 wt% MXene and 6 wt% Co). Additionally, the synergism between the foam structure and TiO2 nanocrystals resulted in improved thermal conductivity, ranging from 1.28 W/(m·K) to 1.36 W/(m·K), which were 2–6 times higher than that in the solid composite films. This study provided new insights into the simultaneously enhanced EMW absorption and dissipating heat ability in polymer composite foams with a low percolation threshold.

Exploring lightweight electromagnetic wave absorption materials is urgently needed to satisfy the miniaturization and integration of artificial intelligence and 5G technologies. Herein, nitrogen-doped graphene (N-GN) is successfully fabricated through a simple hydrothermal method, which can float in the water. Except for keeping the sheet-like structure of GO, nitrogen-doped graphene shows a reticular-like structure with more wrinkles and crinkles, which is crossed and interconnected to each other. The introduced nitrogen heteroatoms may induce dipole polarization, and the special interconnected reticular-like structure may improve the energy dissipation capacity. These features make nitrogen-doped graphene process improved dielectric loss and enhanced electromagnetic wave absorption performance. When the mass fraction of N-GN is only 10 wt%, N-GN shows a maximum reflection loss value of − 21.7 dB at 14.3 GHz with an absorber thickness of only 1.78 mm. This work indicates that nitrogen-doped graphene is a good candidate of lightweight dielectric materials.

In addition to the demand of thin, lightweight, broadband and high-efficient characteristics, exploring microwave absorbents with superior resistance to oxidation and corrosion is urgently need for practical applications. Herein, carbon nanofibers embedded by α-Fe2O3, Fe or Fe3C nanocrystals are prepared through electrospinning technique followed by carbonization in different atmospheres. The one-dimensional structures can intertwine into three-dimensional conductive network, which is favored for energy dissipation. The Fe3C/N-doped carbon nanofibers show boosting microwave absorption properties compared to the bare carbon, α-Fe2O3/C and Fe/C nanofibers. The Fe3C/N-doped carbon nanofibers show an optimal reflection loss of −57.9 dB at 5.8 GHz with a thickness of 4.1 mm. Meanwhile, a reflection loss of −54.5 dB can be achieved at 17.8 GHz, when the absorber thickness is only 1.5 mm. The superior microwave absorption properties are attributed to the dipole polarization, interfacial polarization and ferromagnetic resonance, induced by the synergistic effect of Fe3C nanocrystals and carbon nanofibers. Moreover, acid-soaking and air-annealing treatments reveal that the Fe3C/N-doped carbon nanofibers show remarkable corrosion and oxidation resistance. This work suggests that encapsulating magnetic nanocrystals in dielectric carbon-based materials is an efficient strategy to construct high-efficient lightweight microwave absorbents with oxidation/corrosion resistance.

In this work, a novel binder-free electrode, in which three-dimensional porous Ni2P@Ni(OH)2 nanosheet arrays were in situ grown on carbon cloth (CC), is rationally designed for supercapacitor applications. In comparison with Ni2P@CC, the Ni2P@Ni(OH)2@CC electrode represents superior electrochemical characteristics: the gravimetric capacitance and areal capacitance are boosted to be 632 C g−1 and 0.73 C cm−2 at 1 mA cm−2, about 2 and 2.7 times larger than those of Ni2P@CC (321 C g−1 and 0.27 C cm−2), respectively; the rate capability is improved to be 63.3% from 1 to 10 mA cm−2, about 1.5 times larger than Ni2P@CC (42.9%); the cycle stability is enhanced to be 81.4% after 1000 cycles, about 1.6 times larger than Ni2P/CC (51.8%). The assembly Ni2P@Ni(OH)2@CC//AC hybrid supercapacitor device shows high energy density of 23.5 Wh kg−1 at a power density of 1158.0 W kg−1 and good cycling stability of 75.2% maintenance after 5000 cycles. Benefiting from the combined advantages of high electronic conductivity and large specific capacitance of Ni2P, superior anion exchanging/intercalating capacity of Ni(OH)2, excellent flexibility of carbon cloth, and special hierarchical architecture with large surface area, the Ni2P@Ni(OH)2@CC electrode is promised to be a good candidate for supercapacitors.

The impedance matching is a very important part to influence materials’ microwave absorption performance. However, a way to further discuss the impedance matching is still weak. We build a novel dielectric–magnetic impedance matching (DMIM) model to analyze the real part and imaginary part of materials’ impedance matching. To verify the practicality of the DMIM model, using MIL-100(Fe) as precursor, a series of FexNi1−x@C are synthesized via one-step pyrolysis by controlling the samples’ Fe–Ni ratio, changing their dielectric loss tangent and magnetic loss tangent and successfully regulating their impedance matching to optimize microwave absorption properties. In addition, the minimum reflection loss for MOF-derived Fe0.8Ni0.2@C can arrive at -71.3 dB at 10.3 GHz with a thickness of 3.1 mm, and the effective absorption bandwidth is 5.3 GHz. And combining with the RLGC equivalent circuit model to further indicate the FexNi1−x@C’s energy loss mechanism. The method of using DMIM model and RLGC model to discuss materials’ impedance matching and energy loss mechanism paves a new way to fabricate high-performance microwave materials with balanced electromagnetic distribution and further reveal the materials' microwave absorbing mechanism.

Introduction of defects and engineering of structure play significant roles in improvement on electrochemical performances of copper sulfide (Cu9S5) as a supercapacitors (SCs) electrode. Herein, a hierarchical rose-shaped Cu9S5 is synthesized by using a facile one-step hydrothermal method and subsequently annealed under different atmospheres and time. X-ray photoelectron spectroscopy (XPS) spectra and scanning electron microscopy (SEM) confirm the presence of sulfur vacancies and changes of morphology in Cu9S5 annealed under argon (Ar) for 2 h (Cu9S5-Ar-2h), which exhibit an effective promotion to the surface redox reactions and ion transition ability proved by the electrochemical measurements. Thus, when the Cu9S5-Ar-2h is used as an SCs electrode, it performs the highest specific capacity of 337 C/g at a scanning rate of 5 mV/s, which is nearly four times that of the pristine Cu9S5 (92 C/g). Moreover, an asymmetric supercapacitor using Cu9S5-Ar-2h as a positive electrode and activated carbon as a negative electrode is designed and assembled, which demonstrates a good energy density of 13.2 Wh/kg at a power density of 789.5 W/kg and an outstanding cycling stability of near 100% after 2000 cycles. This work will provide a feasible strategy to construct advanced electrodes based on transition metal sulfides by annealing treatments.

MIL-100(Fe)-derived unique porous iron has excellent microwave-absorbing performance and exhibits dielectric loss mechanism. A great microwave reflection loss (RL) of − 75.3 dB can be obtained and its effective absorption bandwidth is 4 GHz. This excellent microwave absorption performance mainly originates from dielectric loss rather than magnetic loss of the incoming microwave field. The impedance matching, multiple reflection and scattering loss and interface polarization of the porous ions could be tuned by controlling the reaction temperature and gas environment. Meanwhile, this study provides a new inspiration and insight for preparing dielectric loss iron with an excellent microwave absorption performance, which encourages achievements light the way to the development of the dielectric loss metal absorbents.

Herein, NiCoP nanoparticles decorated on reduced graphene oxide (rGO) were synthesized through a two-step hydrothermal-phosphorization route as enhanced microwave absorbers. Microstructure investigations indicate that NiCoP nanoparticles are uniformly anchored on the surface of rGO. Compared with the bare NiCoP, NiCoP/rGO nanocomposites reveal clearly improved microwave absorbing performance. The strongest reflection loss (RL) values of NiCoP/rGO hybrid absorber can reach −20.61 dB at 6.43 GHz with a matching thickness of 4.4 mm, and a broad effective absorption bandwidth (RL

Ultrathin freestanding membranes with a pronounced metal-insulator transition (MIT) have huge potential for future flexible electronic applications as well as provide a unique aspect for the study of lattice-electron interplay. However, the reduction of the thickness to an ultrathin region (a few nm) is typically detrimental to the MIT in epitaxial films, and even catastrophic for their freestanding form. Here, we report an enhanced MIT in VO

In this work, a novel binder-free electrode, in which three-dimensional porous Ni2P@Ni(OH)2 nanosheet arrays were in-situ grown on carbon cloth (CC), is rationally designed for supercapacitor applications. In comparison with Ni2P@CC, the Ni2P@Ni(OH)2@CC electrode represents superior electrochemical characteristics: the gravimetric capacitance and areal capacitance are boosted to be 632 C g-1 and 0.73 C cm-2 at 1 mA cm-2, about 2 and 2.7 times larger than those of Ni2P@CC (321 C g-1 and 0.27 C cm-2), respectively; the rate capability is improved to be 63.3% from 1 to 10 mA cm-2, about 1.5 times larger than Ni2P@CC (42.9%); the cycle stability is enhanced to be 81.4% after 1000 cycles, about 1.6 times larger than Ni2P/CC (51.8%). The assembly Ni2P@Ni(OH)2@CC//AC hybrid supercapacitor device shows high energy density of 23.5 Wh kg-1 at a power density of 1158.0 W kg-1 and good cycling stability of 75.2% maintenance after 5000 cycles. Benefiting from the combined advantages of high electronic conductivity and large specific capacitance of Ni2P, superior anion exchanging/intercalating capacity of Ni(OH)2, excellent flexibility of carbon cloth and special hierarchical architecture with large surface area, the Ni2P@Ni(OH)2@CC electrode is promised to be a good candidate for supercapacitors.

Ultrathin freestanding membranes with a pronounced metal–insulator transition (MIT) have huge potential for future flexible electronic applications as well as provide a unique aspect for the study of lattice–electron interplay. However, the reduction of the thickness to an ultrathin region (a few nm) is typically detrimental to the MIT in epitaxial films, and even catastrophic for their freestanding form. Here, we report an enhanced MIT in VO2-based freestanding membranes, with a lateral size up to millimeters and the VO2 thickness down to 5 nm. The VO2 membranes were detached by dissolving a Sr3Al2O6 sacrificial layer between the VO2 thin film and the c-Al2O3(0001) substrate, allowing the transfer onto arbitrary surfaces. Furthermore, the MIT in the VO2 membrane was greatly enhanced by inserting an intermediate Al2O3 buffer layer. In comparison with the best available ultrathin VO2 membranes, the enhancement of MIT is over 400% at a 5 nm VO2 thickness and more than 1 order of magnitude for VO2 above 10 nm. Our study widens the spectrum of functionality in ultrathin and large-scale membranes and enables the potential integration of MIT into flexible electronics and photonics. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version

Dual-functional magnetic/dielectric Fe/Fe3C@C composites were fabricated by pyrolysis of MIL-88B (Fe) in an Ar atmosphere, which was used for microwave absorption and electromagnetic interference (EMI) shielding. The Fe/Fe3C nanocrystals were completely encapsulated in crystalline carbon, which can improve oxidation resistance capacity. Owing to remarkable impedance matching and strong attenuation constants, the Fe/Fe3C@C composites show an optimal reflection loss (RL) value of −56.4 dB at 14.0 GHz and a broad effective absorption bandwidth (RL ⩽ −10 dB) of 4.8 GHz when the filling ratio and absorber thickness are only 20 wt% and 1.9 mm, respectively. Resulting from the high conductivity of crystalline carbon, magnetic loss of Fe/Fe3C, and core–shell structure, the Fe/Fe3C@C composites also show remarkable EMI shielding properties at the X band, which are enhanced by increasing the filling ratio of the Fe/Fe3C@C composites. When the filling ratio is 50 wt%, the EMI shielding efficiency can reach 35 dB. This work suggests that magnetic/dielectric Fe/Fe3C@C is a good candidate in microwave absorption and EMI shielding.

A novel Sodium Carbonate (Na2CO3) promoted ultrasonic exfoliation (NPUE) method was proposed for the high efficiency preparation of high-quality two-dimensional (2D) Gallium Selenide (GaSe) nanosheets in isopropanol (IPA). It is found that Na2CO3 acting as an accelerant could enhance the exfoliation efficiency up to 40 times and increase the concentration for the dispersion of GaSe, which could quickly reach 1.2 mg mL−1 when the initial amount of GaSe and Na2CO3 is 30:30. A series of characterization show that bulk GaSe has been successfully exfoliated into single- to few-layer GaSe nanosheets.

Co-doped ZnO nanoparticles with different dosage concentrations were fabricated by a thermal decomposition method. The nanoparticles show a pure wurtzite structure without the formation of a secondary phase or Co clusters, in which Co ions present as Co2+ and occupy Zn2+ tetrahedral sites within the ZnO matrix. All the samples show ferromagnetic properties at room temperature with nonzero coercivity and remanence magnetization. Besides, the magnetic data is also fitted by the model of bound magnetic polarons (BMP). By increasing the Co2+ doping concentration, the saturation magnetization values of Co-doped ZnO nanoparticles increase first and then decreases, which is related to the variation tendency of oxygen defects on the surface and the number of BMPs. This phenomenon can be ascribed to the formation of defect-induced BMPs, in which ferromagnetic coupling occurs at lower Co2+ concentration and Co2+–O2−–Co2+ antiferromagnetic coupling arises at higher Co2+ concentration. Air annealing experiments further demonstrate this result, in which the saturation magnetization of Co-doped ZnO nanoparticles is reduced after annealing in Air. The doping effect and oxygen defects on the magnetic ordering of Co-doped ZnO were calculated using density functional theory. The calculation results reveal that stable long-range magnetic ordering in Co-doped ZnO nanoparticles is mainly attributed to the localized spin moments from 3d electrons of Co2+ ions. Both the experimental and theoretical studies demonstrate that the ferromagnetism in Co-doped ZnO nanoparticles is originated from the combined effects of Co doping and oxygen vacancies. These results provide an experimental and theoretical view to understand the magnetic origination and tune the magnetic properties of diluted magnetic semiconductors, which is of great significance for spintronics.

Lightweight, strong and broadband microwave absorbents are urgently demanded for practical applications. Exploring magnetic/dielectric composites by anchoring magnetic nanostructures on lightweight dielectric carbon is an effective way, due to their possible good impedance matching condition. Herein, one-dimensional FeCo/C nanofibers are fabricated by electrospinning method and subsequent anoxic annealing treatment, which are used as difunctional magnetic/dielectric microwave absorbents. The nanofibers have a large aspect ratio, in which tiny magnetic FeCo nanocrystals are uniformly decorated in the amorphous dielectric C nanofibers. Benefiting from good impedance matching condition, enhanced microwave attenuation ability and synergistic effect between ferromagnetic FeCo and dielectric C, the FeCo/C nanofibers exhibit boosting microwave absorption performance, which is related to the absorber thickness and filling ratio. The optimal FeCo/C/paraffin composites with 40 wt% of functional fillers show a minimum reflection loss value of −59.9 dB with broad effective absorption bandwidth of 6.0 GHz at 13.2 GHz when the absorber thickness is only 2.6 mm. The FeCo/C nanofibers have a small density of only about 1.1 g/cm3, much smaller than the bulk FeCo (7.4–7.6 g/cm3). Owing to the characteristics of low density, strong absorption and broad effective absorption bandwidth, the FeCo/C nanofibers are promised to be good candidates as microwave absorbents.

A novel strategy of boosting electrochemical performance of hybrid supercapacitor cathode based on interface engineering by fabrication of Schottky-type conjunction is proposed. The electrode is composed of binder free 3D CoP nanoflowers decorated by CeO2 nanoparticles, which was directly grown on nickel foam, forming a conjunction interface. Compared to CoP, the CeO2@CoP electrode exhibits remarkable enhanced electrochemical performance. The significantly boosted performance can be attributed to the CeO2@CoP interface, which promotes electrons migration from CoP to CeO2 and eventually forms positive holes on CoP. These positive holes can easily capture more OH−, creating more active sites for redox process. Furthermore, a hybrid supercapacitor full cell composed of CeO2@CoP and activated carbon was assembled, which exhibits outstanding energy storage performance with a specific capacity of 486.5 mC cm−2 at 1 mA cm−2 and outstanding cycle stability of 89% after 5000 cycles. The energy density is 55.4 Wh kg−1 at a power density of 955.9 W kg−1. This work not only demonstrates that CeO2 is an attractive additive for supercapacitor electrodes, but also provides an experimental/theoretical understanding of the enhanced electrochemical performance by electrons migration process on CeO2@CoP interfaces, which is important for the design of supercapacitors.

High-quality neodymium oxychlorides nanocrystals with cubic shape were synthesized by a nonhydrolytic thermolysis route. The morphology and crystal structure of the neodymium oxychlorides nanocubes were characterized by transmission electron microscopy at the nanoscale. Transmission electron microscope (TEM) image shows that the neodymium oxychlorides nanocrystals are nearly monodispersed with cube-like shape. X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns of numerous neodymium oxychlorides nanocubes suggest a pure crystal phase with tetragonal PbFCl matlockite structure. HRTEM image of individual neodymium oxychlorides nanocubes indicate that each nanocubes have a single-crystalline nature with high quality. Unlike the anti-ferromagnetism of the bulk, the neodymium oxychlorides nanocubes show clearly anomalous ferromagnetic characteristic at room temperature. This finding provides a new platform for the exploration of diluted magnetic semiconductors, rare earth-based nanomaterials and so on.