Heterogeneous interfaces in 3D interconnected networks of flower-like 1T/2H Molybdenum disulfide nanosheets and carbon-fibers boosts superior EM wave absorption.

With the wide application of electromagnetic waves in national defense, communication, navigation and home appliances, the electromagnetic pollution problem is becoming more and more prominent. Therefore, high-performance, and low-density composite wave-absorbing materials have attracted much attention. In this paper, three-dimensional (3D) network structures of flower-like 1T/2H Molybdenum disulfide nanosheets anchored to carbon fibers (1T/2H MoS2/CNFs) were prepared by electrostatic spinning technique and calcination process. The morphology and electromagnetic wave absorption properties were tuned by changing the content of flower-like MoS2. The optimized 1T/2H MoS2/CNFs composite exhibits superior electromagnetic wave absorption with minimum reflection (RLmin) of -42.26 dB and effective absorption bandwidth (EAB) of 6.48 GHz at 2.5 mm. Multi-facts contribute to the super performance. First, the uniquely designed nanosheet and 3D interconnected networks leads to multiple reflection and scattering of electromagnetic waves, which promotes the attenuation of electromagnetic waves. Second, the propriate content of CNFs and MoS2 with different phase regulates its impedance matching characteristic. Third, Numerous heterogeneous interfaces existed between CNFs and MoS2, 1T and 2H MoS2 phase results in interface polarization. Besides, the 1T/2H MoS2 rich in defects induces defect polarization, improving the dielectric loss. Furthermore, the electromagnetic wave absorption performance was proved via radar reflectance cross section simulation. This work illustrates 1T/2H MoS2/CNFs is a promising material for electromagnetic absorption with wide bandwidth, strong absorption, low density, and high thermal stability.

In Situ Loading of Ni3ZnC0.7 Nanoparticles with Carbon Nanotubes to 3D Melamine Sponge Derived Hollow Carbon Skeleton toward Superior Microwave Absorption and Thermal Resistance.

The simple and low-cost construction of a 3D network structure is an ideal way to prepare high-performance electromagnetic wave (EMW) absorption materials. Herein, a series of carbon skeleton/carbon nanotubes/Ni3ZnC0.7 composites (CS/CNTs/Ni3ZnC0.7) are successfully prepared by in situ growth of Ni3ZnC0.7 and CNTs on 3D melamine sponge carbon. With the increase of precursor, Ni3ZnC0.7 nanoparticles nucleate and catalyze the generation of CNTs on the surface of the carbon skeleton. The minimum reflection loss (RL) value of the S60min composite (loading time of 60 min) reaches -86.6 dB at 1.6 mm and effective absorption bandwidth (EAB, RL≤-10 dB) is up to 9.3 GHz (8.7-18 GHz). The 3D network sponge carbon with layered micro/nanostructure and hollow skeleton promotes multiple reflection and absorption mechanisms of incident EMW. The N-doping and defects can be equivalent to an electric dipole, providing dipole polarization to increase dielectric relaxation. The uniform Ni3ZnC0.7 nanoparticles and CNTs play a key role in dissipating electromagnetic energy, blocking heat transfer, and enhancing the mechanical properties of the skeleton. Fortunately, the composite displays a quite low thermal conductivity of 0.09075 W m·K-1 and good flexibility, which can provide insulation and quickly recover to its original state after being stressed.

Thermal stability of Ni3ZnC0.7: As tunable additive for biomass-derived carbon sheet composites with efficient microwave absorption.

With the rapidly development of radar detection technology and the increasingly complex application environment in military field and electromagnetic pollution surrounded by electron devices, increasingly demand is needed for electromagnetic wave absorbent materials with high absorption efficiency and thermal stability. Herein, a novel Ni3ZnC0.7/Ni loaded puffed-rice derived carbon (RNZC) composites are successfully prepared by vacuum filtration of metal-organic frameworks gel precursor together with layered porous-structure carbon and followed by calcination. The Ni3ZnC0.7 particles uniformly decorate on the surface and pores of puffed-rice derived carbon. The puffed-rice derived carbon@Ni3ZnC0.7/Ni-400 mg (RNZC-4) sample displayed the best electromagnetic wave absorption (EMA) performances among the samples with different Ni3ZnC0.7 loading. The minimum reflection loss (RLmin) of the RNZC-4 composite reaches -39.9 dB at 8.6 GHz, while widest effective absorption bandwidth (EAB) of RNZC-4 for RL < -10 dB can reach 9.9 GHz (8.1-18 GHz, 1.49 mm). High porosity and large specific surface area promote the multiple reflection-absorption effect of the incident electromagnetic waves. The Ni3ZnC0.7 nanoparticles provide a large number of interfaces and dipole factors. Analysis reveals that the RNZC-4 remained general stability under 400 °C with formation of a small amount of NiO and ZnO phases. Surprisingly, at such high temperature, the absorbing properties of the material are improved rather than decreased. Obviously, the material still maintains good electromagnetic wave performance at high temperature, and implies that the absorber shows good performance stability. Therefore, our preparations exhibit potential applications under extreme conditions and a new insight for the design and application of bimetallic carbides.

Phase Transformation and Performance of Mg-Based Hydrogen Storage Material by Adding ZnO Nanoparticles.

ZnO nanoparticles in a spherical-like structure were synthesized via filtration and calcination methods, and different amounts of ZnO nanoparticles were added to MgH2 via ball milling. The SEM images revealed that the size of the composites was about 2 µm. The composites of different states were composed of large particles with small particles covering them. After the absorption and desorption cycle, the phase of composites changed. The MgH2-2.5 wt% ZnO composite reveals excellent performance among the three samples. The results show that the MgH2-2.5 wt% ZnO sample can swiftly absorb 3.77 wt% H2 in 20 min at 523 K and even at 473 K for 1 h can absorb 1.91 wt% H2. Meanwhile, the sample of MgH2-2.5 wt% ZnO can release 5.05 wt% H2 at 573 K within 30 min. Furthermore, the activation energies (Ea) of hydrogen absorption and desorption of the MgH2-2.5 wt% ZnO composite are 72.00 and 107.58 KJ/mol H2, respectively. This work reveals that the phase changes and the catalytic action of MgH2 in the cycle after the addition of ZnO, and the facile synthesis of the ZnO can provide direction for the better synthesis of catalyst materials.

Hierarchical engineering of Large-caliber carbon Nanotube/Mesoporous Carbon/Fe3C nanoparticle hybrid nanocomposite towards Ultra-lightweight electromagnetic microwave absorber.

The rational regulation of the magnetic-dielectric composition and microstructures of the absorber is considered an important approach to optimize both the impedance matching and the electromagnetic microwave attenuation ability. Along these lines, a novel architecture-controlled large-caliber carbon nanotube/mesoporous carbon/Fe3C nanoparticle-based hybrid nanocomposites (CNT/C/Fe3C), which were derived from the CNT/polyimide (PI) assemblies anchoring ferric oxide hydrate nanoprecipitates, are presented in this work. The proposed configurations were prepared by applying a cooperative co-assembly strategy and high-temperature pyrolysis procedure for the development of an ultra-lightweight electromagnetic microwave absorber. The employed hierarchically tubular heterogeneous architecture is composed of a highly graphited CNT supporting skeleton, polyimide assemblies-converted carbon interlayer with mesopores, and uniformly distributed magnetic Fe3C nanoparticles. This unique hierarchical structure can not only induce multiple reflection and scattering effects of the incident electromagnetic microwave but also trigger dipole/interfacial polarization, ferromagnetic resonance and eddy current loss that are beneficial for the synergistic dielectric and magnetic loss. Moreover, the large-caliber CNT and mesoporous carbon interlayer can endow the as-prepared absorber with lightweight characteristics. Hence, the proposed CNT/C-EDA/Fe3C-900 hybrid nanocomposite exhibits a minimum reflection loss (RL) of -48.4 dB at a matching thickness of 3.2 mm, and the effective absorption bandwidth (RL ≤ -10 dB) almost covers the whole X-band only with a 5 wt% filler loading. Undoubtedly, these encouraging outcomes will promote the development of hierarchical engineering techniques of novel magnetic-dielectric nanocomposite absorbers.

Multiple reflection and scattering effects of the lotus seedpod-based activated carbon decorated with Co3O4 microwave absorbent.

The lotus seedpod-based activated carbon (LSAC) is derived from pyrolysis of lotus seedpod as biomass carbon precursor, and Co3O4 is then deposited to LSAC by oxidation-precipitation and crystallization process of Co ions from Co(NO3)2 solution. The Co3O4 particles uniformly decorate on the surface and/or the inner channels of LSAC. The optimal reflection loss (RL) value of LSAC/Co3O4-paraffin wax (PW) composite reaches -39.8 dB, and the bandwidth for RL below -10 dB and -20 dB are 10.3 and 3.0 GHz, respectively, much better than that of LSAC-PW composite for the higher magnetic loss. The addition of Co3O4 particles in LSAC-PW composite significantly enhance the RL values in various thicknesses. The channels of the LSAC and decorated Co3O4 can improve the abilities of multiple scattering, dipole polarization, interface polarization and magnetic loss. This composite provides a promising method to construct high performance absorbers by using biomass carbon to tune the dielectric properties of the ferromagnetic materials.

Agaric-like anodes of porous carbon decorated with MoO2 nanoparticles for stable ultralong cycling lifespan and high-rate lithium/sodium storage.

The agaric-like anodes of porous carbon decorated with MoO2 nanoparticles (MoO2/C) for reversible Li/Na storage were synthesized via a green and facile bio-inspired route. The uniformly distributed MoO2 nanoparticles, the porous agaric-like carbon matrix and high degree graphitization of carbon materials, effectively mitigated the huge volume changes during cycling and improved the reversible capacity, resulting in the outstanding electrochemical behaviors with excellent rate capability, high capacity and excellent stable long cycling lifespan as anodes for lithium and sodium storage. Especially, the MoO2/C electrodes showed ultralong cycling performance under high current density of 5.0 A g-1, presenting a reversible capacity of 363.2 mAh g-1 after a prolonged 2000-cycles as anodes for Li storage. Meanwhile, the MoO2/C electrodes displayed a super-long cycling lifespan of 3000 cycles with the reversible discharge capacity of 193.5 mAh g-1 at the current density of 5.0 A g-1 for Na storage. Furthermore, the kinetic analysis of MoO2/C-4 electrodes as anodes for Li/Na storage was carried out to further investigate the electrochemical behavior. The ultralong cycling performance under high-density could satisfy the demands of next-generation anode electrodes for Li/Na ion batteries, promoting the commercialization process of MoO2-based materials.

Facile Electrochemical Method for the Fabrication of Stable Corrosion-Resistant Superhydrophobic Surfaces on Zr-Based Bulk Metallic Glasses.

Both surface microstructure and low surface energy modification play a vital role in the preparation of superhydrophobic surfaces. In this study, a safe and simple electrochemical method was developed to fabricate superhydrophobic surfaces of Zr-based metallic glasses with high corrosion resistance. First, micro-nano composite structures were generated on the surface of Zr-based metallic glasses by electrochemical etching in NaCl solution. Next, stearic acid was used to decrease surface energy. The effects of electrochemical etching time on surface morphology and wettability were also investigated through scanning electron microscopy and contact angle measurements. Furthermore, the influence of micro-nano composite structures and roughness on the wettability of Zr-based metallic glasses was analysed on the basis of the Cassie-Baxter model. The water contact angle of the surface was 154.3° ± 2.2°, and the sliding angle was <5°, indicating good superhydrophobicity. Moreover, the potentiodynamic polarisation test and electrochemical impedance spectroscopy suggested excellent corrosion resistance performance, and the inhibition efficiency of the superhydrophobic surface reached 99.6%. Finally, the prepared superhydrophobic surface revealed excellent temperature-resistant and self-cleaning properties.

Efficient microwave absorber and supercapacitors derived from puffed-rice-based biomass carbon: Effects of activating temperature.

Biomass-based carbon is gaining increasing attention because it presents a promising prospect for economic growth and social sustainable development. Moreover, it is an excellent medium for application in electromagnetic and electronic devices. Here, puffed-rice-based carbon is obtained at various activating temperatures, and when the hollow bulges on the carbon disappear, the morphology of the carbon changes into sheet-like structures. The R-800 sample displays the highest ID/IG value and demonstrates the best performance when used as both a microwave absorber and an electrode material. The minimum reflection loss (RL) and bandwidth for RL < -10 dB of the R-800 sample reach -72.1 dB and 13.2 GHz, respectively, and the bandwidth for RL < -20 dB is as large as 7.0 GHz, illustrating the widest bandwidth among the five carbon specimens. The multiple reflection effects and scattering, good impedance matching, and interfacial polarization synergistically enhance the microwave absorption performances of the sample. At 1 A g-1, the specific capacitance of the R-800 sample reaches 117.2 F g-1 and the capacitance retention remains at 85.3%. Moreover, a hybrid supercapacitor R-800//R-800 demonstrates an outstanding energy density of 15.23 Wh kg-1, power density of 5739.43 W kg-1, and high cycle stability (94.5% after 5000 cycles). This functionalized biomass carbon provides a promising media for constructing a bridge between sustainable development and biomass materials.

Bead-like cobalt nanoparticles coated with dielectric SiO2 and carbon shells for high-performance microwave absorber.

The development of high-efficiency microwave absorption materials with both strong absorption intensity and wide absorption bandwidth is still a significant challenge. In this work, the bead-like cobalt nanoparticles of 50 nm with strong magnetic loss capability are prepared by hydrogen plasma-metal reaction. To further regulate the dielectric parameters, the carbon, SiO2, and SiO2/carbon shells are coated on the bead-like cobalt cores by in-situ polymerization of silica and phenolic resin to obtain the Co@C, Co@SiO2, and Co@SiO2@C nanocomposites, respectively. The Co@SiO2@C nanocomposite possesses the best electromagnetic wave (EMW) absorption performances among the samples. At the thickness of only 1.7 mm, the minimum reflection loss (RL) value of -39.6 dB at 13.5 GHz and the effective absorption bandwidth (EAB) of 7.6 GHz for RL < -10 dB are simultaneously obtained. Surprisingly, the absorption bandwidth (RL < -20 dB) is as wide as 14.2 GHz (3.8-18 GHz) with the thickness of 1.3-5.0 mm. The excellent microwave absorption performances are ascribed to the strong magnetic loss of the bead-like Co, the synergistic effect between multiple components, as well as the multiple polarization and multiple scattering induced by core-shell structure. As a consequence, the Co@SiO2@C nanocomposite can serve as an ideal candidate for high-performance microwave absorption.

High loading nanoconfinement of V-decorated Mg with 1 nm carbon shells: hydrogen storage properties and catalytic mechanism.

Nanoconfinement is an effective strategy for obtaining Mg-based hydrogen storage materials with fast reaction kinetics and decreased operating temperatures. However, the design of high loading nanoconfined Mg with an efficient catalyst remains a great challenge. Herein, we confined V-decorated Mg nanoparticles in 1 nm carbon shells through a reactive gas evaporation method. Due to the ultrathin carbon shells, the loading of the Mg-V@C nanocomposite reached over 94%. By adjusting the evaporation rate of Mg and V, the content of V in the nanocomposite could be accurately controlled from 2 to 25 wt%. Among the samples with different V contents, the Mg92V8@C nanocomposite with an average particle size of 32 nm had the best hydrogen storage properties. It showed a high hydrogen storage capacity of 6.6 wt% and could realize reversible hydrogenation/dehydrogenation cycles with over 5.2 wt% capacity at 473/573 K. The apparent activation energies for hydrogenation and dehydrogenation were reduced to 41 and 67 kJ mol-1, respectively. The improved hydrogen storage properties are attributed to the nanoconfinement effect of the carbon shell and the catalytic effects of VH2/V2H nanoparticles as hydrogen pumps at different temperatures during hydrogenation and dehydrogenation.

Formation of Multiple-Phase Catalysts for the Hydrogen Storage of Mg Nanoparticles by Adding Flowerlike NiS.

In order to enhance the hydrogen storage properties of Mg, flowerlike NiS particles have been successfully prepared by solvothermal reaction method, and are subsequently ball milled with Mg nanoparticles (NPs) to fabricate Mg-5 wt % NiS nanocomposite. The nanocomposite displays Mg/NiS core/shell structure. The NiS shell decomposes into Ni, MgS and Mg2Ni multiple-phases, decorating on the surface of the Mg NPs after the first hydrogen absorption and desorption cycle at 673 K. The Mg-MgS-Mg2Ni-Ni nanocomposite shows enhanced hydrogenation and dehydrogenation rates: it can quickly uptake 3.5 wt % H2 within 10 min at 423 K and release 3.1 wt % H2 within 10 min at 573 K. The apparent hydrogen absorption and desorption activation energies are decreased to 45.45 and 64.71 kJ mol-1. The enhanced sorption kinetics of the nanocomposite is attributed to the synergistic catalytic effects of the in situ formed MgS, Ni and Mg2Ni multiple-phase catalysts during the hydrogenation/dehydrogenation process, the porthole effects for the volume expansion and microstrain of the phase transformation of Mg2Ni and Mg2NiH4 and the reduced hydrogen diffusion distance caused by nanosized Mg. This novel method of in situ producing multiple-phase catalysts gives a new horizon for designing high performance hydrogen storage material.

The synergistic effects of carbon coating and micropore structure on the microwave absorption properties of Co/CoO nanoparticles.

25 nm carbon-coated microporous Co/CoO nanoparticles (NPs) were synthesized by integrating chemical de-alloying and chemical vapor deposition (CVD) methods. The NPs possess micropores of 0.8-1.5 nm and display a homogeneous carbon shell of about 4 nm in thickness with a low graphitization degree. The saturation magnetization (MS) and coercivity (HC) of the NPs were 70.3 emu g-1 and 398.4 Oe, respectively. The microporous Co/CoO/C NPs exhibited enhanced microwave absorption performance with a minimum reflection coefficient (RC) of -78.4 dB and a wide absorption bandwidth of 8.1 GHz (RC ≤ -10 dB), larger than those of the nonporous counterparts of -68.3 dB and 5.8 GHz. The minimum RC values of the microporous Co/CoO/C NPs at different thicknesses were much smaller than the nonporous counterparts. The high microwave absorption mechanism of the microporous Co/CoO/C nanocomposite can be interpreted in terms of the interfacial polarization relaxation of the core/shell and micropore structures, the effective permittivity modification of the air in the micropores and the polarization relaxation of the defects in the low-graphitization carbon shell and the porous Co NPs. Our study demonstrates that the microporous Co/CoO/C nanocomposite is an efficient microwave absorber with high absorption intensity and wide absorption bandwidth.