General Fabrication of 3D Hierarchically Structured Bamboo-like Nitrogen-Doped Carbon Nanotube Arrays on 1D Nitrogen-Doped Carbon Skeletons for Highly Efficient Electromagnetic Wave Energy Attenuation

Ultrathin Terahertz-Wave Absorber Based on Inorganic Materials for 6G Wireless Communications

Terahertz waves are gathering attention as carrier waves for next-generation wireless communications such as sixth-generation wireless communication networks and autonomous driving systems. Electromagnetic-wave absorbers for the terahertz-wave region are necessary to ensure information security and avoid interference issues. Herein we report a high-performance terahertz-wave absorber composed of a composite of metallic λ-Ti3O5 and insulating TiO2 nanocrystals (λ-Ti3O5@TiO2). This material exhibits a strong terahertz-wave absorption with high values for the real (permittivity, ε') and imaginary parts (dielectric loss, ε″) of the complex dielectric constant. Furthermore, the tan(δ) (≡ ε″/ε') values are significantly high, ranging from 0.50 to 0.76 in the frequency range between 0.1 and 1 THz. An ultrathin film with a thickness of 48 μm recorded a reflection loss of -28 dB (99.8% of the terahertz wave is absorbed by the film). A terahertz-wave absorber with such a small thickness has yet to be developed. Not only does the present material exhibit resistance to heat, light, water, and organic solvents, but it can also be economically fabricated to support various applications, including outdoor uses.

High quality bifunctional cathode for rechargeable zinc-air batteries using N-doped carbon nanotubes constrained CoFe alloy

Building efficient and stable bifunctional electrocatalysts toward oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is crucial for the advancement of rechargeable zinc-air batteries (ZABs). Here, a convenient in situ strategy is reported to controllably encapsulate CoFe alloy nanoparticles within N-doped carbon nanotubes (CoFe@NCNT). The abundant Co(Fe)-Nx active sites and the synergistic interaction between CoFe alloys and carbon nanotubes facilitate mass transfer and interfacial charge transfer, resulting in excellent dual functional electrocatalytic activity of OER/ORR with minor potential difference (ΔE = 0.73 V). Thus, the corresponding rechargeable ZAB displays high power density (194 mW cm-2), excellent specific capacity (795 mAh gZn-1), and favorable stability (900 cycles@5 mA cm-2). This work provides an approach for establishing low-cost bultifunctional electrocatalysts with excellent performance of non-noble metal nanoalloys.

A high-performance, oxidation resistance and flexible Zn@MXene/cellulose nanofibers electromagnetic shielding film

Next-generation wearable electromagnetic interference (EMI) materials need to be provided with oxidation resistance, lightness, and flexibility. In this study, a high-performance EMI film with synergistic enhancement of Zn²⁺@Ti₃C₂T _x MXene/cellulose nanofibers (CNF) was found. The unique Zn@Ti₃C₂T _x MXene/CNF heterogeneous interface facilitates the loss of interface polarization, making the total electromagnetic shielding effectiveness (EMI SE_T) and shielding effectiveness per unit thickness (SE/d) of the films reach 60.3 dB and 5025 dB mm^-1, respectively, in the X-band at the thickness of 12 μm ± 2 μm, significantly exceeding that of other MXene-based shielding materials. In addition, the coefficient of absorption gradually increases with the increasing CNF content. Moreover, under the synergistic effect of Zn²⁺, the film shows excellent oxidation resistance (maintaining stable performance after 30 days), greatly exceeding the previous test cycle. Furthermore, the mechanical performance and flexibility of the film are greatly enhanced (tensile strength at 60 MPa, and maintaining stable performance after 100 times bending tests) due to the CNF and hot-pressing process. Therefore, with the enhancement of the EMI performance, high flexibility and oxidation resistance under high temperature and high humidity conditions, the as-prepared films have wide practical significance and broad application prospects in a series of complex applications, such as flexible wearable fields, ocean engineering fields and high-power device packaging fields.

Multicomponent Nanoparticles Synergistic One-Dimensional Nanofibers as Heterostructure Absorbers for Tunable and Efficient Microwave Absorption

Application of novel radio technologies and equipment inevitably leads to electromagnetic pollution. One-dimensional polymer-based composite membrane structures have been shown to be an effective strategy to obtain high-performance microwave absorbers. Herein, we reported a one-dimensional N-doped carbon nanofibers material which encapsulated the hollow Co3SnC0.7 nanocubes in the fiber lumen by electrospinning. Space charge stacking formed between nanoparticles can be channeled by longitudinal fibrous structures. The dielectric constant of the fibers is highly related to the carbonization temperature, and the great impedance matching can be achieved by synergetic effect between Co3SnC0.7 and carbon network. At 800 °C, the necklace-like Co3SnC0.7/CNF with 5% low load achieves an excellent RL value of - 51.2 dB at 2.3 mm and the effective absorption bandwidth of 7.44 GHz with matching thickness of 2.5 mm. The multiple electromagnetic wave (EMW) reflections and interfacial polarization between the fibers and the fibers internal contribute a major effect to attenuating the EMW. These strategies for regulating electromagnetic performance can be expanded to other electromagnetic functional materials which facilitate the development of emerging absorbers.

Novel MOF-derived 3D hierarchical needlelike array architecture with excellent EMI shielding, thermal insulation and supercapacitor performance

The upcoming 5G era will powerfully promote the development of intelligent society in the future, but it will also bring serious electromagnetic pollution. Thus, the development of efficient, lightweight and multifunctional electromagnetic shielding materials and devices is an important research hotspot around the world. Herein, a novel needlelike Co₃O₄/C array architecture is constructed from MOF precursor via a simple pyrolysis process, and its microstructure is controllably tailored by changing the pyrolysis temperature. The unique 3D hierarchical structure and multiphase components enable the architecture to provide high-efficiency electromagnetic interference (EMI) shielding, along with good thermal insulation. More importantly, the architecture possesses fast ion transport channels, which can be used to construct supercapacitors with high specific capacitance and excellent cycle stability. Obviously, this work offers a new inspiration for the design and construction of multifunctional electromagnetic materials and devices.

CoNi Nanoparticles Supported on N-Doped Bifunctional Hollow Carbon Composites as High-Performance ORR/OER Catalysts for Rechargeable Zn-Air Batteries

Searching for high-quality air electrode catalysts is the long-term goal for the practical application of Zn-air batteries. Here, a series of coexistent composite materials (CoNi/NHCS-TUC-x) of cobalt-nickel supported on nitrogen-doped hollow spherical carbon and tubular carbon are obtained using a simple pyrolysis strategy. Co and Ni in the composites are mainly present in the form of alloy nanoparticles, M-N_x and M-C_x (M = Co or Ni) species, with high oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) electroactivity. The materials containing different proportions of spherical carbon and tubular carbon obtained by simply adjusting the raw materials for generating tubular carbon exhibit interesting bifunctional performance: samples with an abundant tubular content have the highest ORR onset potential (0.91 V vs reversible hydrogen electrode), while those with a rich spherical content have the highest ORR current density (5.13 mA·cm^-2). Furthermore, CoNi/NHCS-TUC-3 provides the lowest potential difference (ΔE = E_j=10 - E_1/2) of 0.806 V. We then test the potential possibility of CoNi/NHCS-TUC-3 as an air electrode for primary and rechargeable Zn-air batteries. The primary battery delivers an open-circuit potential of 1.59 V, a peak power density of 361.8 mA·cm^-2, and a specific capacity of 756.5 mA h·g_Zn^-1. The rechargeable battery could be cycled stably for more than 55 h at 10 mA·cm^-2. These characteristics make CoNi/NHCS-TUC-3 a superior electrocatalyst for both the ORR and OER, as well as a suitable bifunctional electrode applied to a rechargeable Zn-air battery.

A generalizable strategy for constructing ultralight three-dimensional hierarchical network heterostructure as high-efficient microwave absorber

Using previous models and theories to construct and develop high-efficient microwave absorbers (MAs) should be a strategic and effective ways to optimize the electromagnetic wave attenuation. Herein, the ultralow density and flexible graphene oxide foam (GOF) and reduced graphene oxide foam (RGOF)/MoS₂ nanosheets were designed and fabricated by the method of chemical vapor deposition and hydrothermal reaction. The obtained GOF and RGOF/MoS₂ samples exhibited very excellent microwave absorption properties while their densities were merely 0.0082 and 0.0084 g•cm^-3, respectively. More importantly, benefiting from the excellent synergistic effect between RGOF and MoS₂, the designed RGOF/MoS₂ well inherited the combined advantages of GOF and MoS₂ in terms of strong absorption abilities, broad absorption bandwidth and thin matching thicknesses. The values of minimum reflection loss and effective frequency bandwidth for RGOF/MoS₂ sample could reach up to -62.92 dB with the matching thickness of 2.27 mm and 4.48 GHz with the matching thickness of 2.12 mm, which were very desirable for high-performance MAs. Moreover, the obtained results indicated that the microwave absorption properties of RGOF/MoS₂ sample could be further optimized by regulating the MoS₂ content. Therefore, a new and effective strategy was proposed to develop high efficiency MAs with ultra-lightweight, wide-band, thin thickness and strong absorption capabilities.

3D Seed-Germination-Like MXene with In Situ Growing CNTs/Ni Heterojunction for Enhanced Microwave Absorption via Polarization and Magnetization

Benefiting from the possible "seed-germination" effect, the "seeds" Ni²⁺ grow into "buds" Ni nanoparticles and "stem" carbon nanotubes (CNTs) from the enlarged "soil" of MXene skeleton. Compared with the traditional magnetic agglomeration, the MXene-CNTs/Ni hybrids exhibit the highly spatial dispersed magnetic architecture. 3D MXene-CNTs/Ni composites hold excellent microwave absorption performance (-56.4 dB at only 2.4 mm). Ti₃C₂T_x MXene is widely regarded as a potential microwave absorber due to its dielectric multi-layered structure. However, missing magnetic loss capability of pure MXene leads to the unmatched electromagnetic parameters and unsatisfied impedance matching condition. Herein, with the inspiration from dielectric-magnetic synergy, this obstruction is solved by fabricating magnetic CNTs/Ni hetero-structure decorated MXene substrate via a facile in situ induced growth method. Ni²⁺ ions are successfully attached on the surface and interlamination of each MXene unit by intensive electrostatic adsorption. Benefiting from the possible "seed-germination" effect, the "seeds" Ni²⁺ grow into "buds" Ni nanoparticles and "stem" carbon nanotubes (CNTs) from the enlarged "soil" of MXene skeleton. Due to the improved impedance matching condition, the MXene-CNTs/Ni hybrid holds a superior microwave absorption performance of - 56.4 dB at only 2.4 mm thickness. Such a distinctive 3D architecture endows the hybrids: (i) a large-scale 3D magnetic coupling network in each dielectric unit that leading to the enhanced magnetic loss capability, (ii) a massive multi-heterojunction interface structure that resulting in the reinforced polarization loss capability, confirmed by the off-axis electron holography. These outstanding results provide novel ideas for developing magnetic MXene-based absorbers.

Diamond-Like Carbon (DLC) Coatings: Classification, Properties, and Applications

DLC coatings have attracted an enormous amount of interest for science and engineering applications. DLC occurs in several different kinds of amorphous carbon materials. Owing to the extensive diversity in their properties, DLC coatings find applications in mechanical, civil, aerospace, automobile, biomedical, marine, and several other manufacturing industries. The coating life of DLC is predominately influenced by its constituent elements and manufacturing techniques. Numerous researchers have performed multiple experiments to achieve a robust understanding of DLC coatings and their inherent capabilities to enhance the life of components. In this review, a wide range of DLC coatings and their classification, properties, and applications are presented. Their remarkable performance in various applications has made DLC coatings a promising alternative over traditional solitary-coating approaches.

Environmentally Friendly and Multifunctional Shaddock Peel-Based Carbon Aerogel for Thermal-Insulation and Microwave Absorption

The eco-friendly shaddock peel-derived carbon aerogels were prepared by a freeze-drying method. Multiple functions such as thermal insulation, compression resistance and microwave absorption can be integrated into one material-carbon aerogel. Novel computer simulation technology strategy was selected to simulate significant radar cross-sectional reduction values under real far field condition. . Eco-friendly electromagnetic wave absorbing materials with excellent thermal infrared stealth property, heat-insulating ability and compression resistance are highly attractive in practical applications. Meeting the aforesaid requirements simultaneously is a formidable challenge. Herein, ultra-light carbon aerogels were fabricated via fresh shaddock peel by facile freeze-drying method and calcination process, forming porous network architecture. With the heating platform temperature of 70 °C, the upper surface temperatures of the as-prepared carbon aerogel present a slow upward trend. The color of the sample surface in thermal infrared images is similar to that of the surroundings. With the maximum compressive stress of 2.435 kPa, the carbon aerogels can provide favorable endurance. The shaddock peel-based carbon aerogels possess the minimum reflection loss value (RL_min) of - 29.50 dB in X band. Meanwhile, the effective absorption bandwidth covers 5.80 GHz at a relatively thin thickness of only 1.7 mm. With the detection theta of 0°, the maximum radar cross-sectional (RCS) reduction values of 16.28 dB m² can be achieved. Theoretical simulations of RCS have aroused extensive interest owing to their ingenious design and time-saving feature. This work paves the way for preparing multi-functional microwave absorbers derived from biomass raw materials under the guidance of RCS simulations.

Highly stretchable and self-foaming polyurethane composite skeleton with thermally tunable microwave absorption properties

Stretchable and lightweight polymer composite material possessing tunable microwave absorption (MA) properties under thermal radiations remain a significant challenge. Here, we proposed a facile strategy to fabricate stretchable, magnetic composite skeletons by incorporating the tadpole-like CNTs@Fe₃O₄nanoparticles into self-foaming polyurethane (PU) matrix and the electromagnetic responsive of CNTs@Fe₃O₄/PU composite foams with different CNTs contents under heating-cooling cycle in a temperature range of 253 -333 K were carefully investigated. Enhanced complex permittivity and shifting peak frequency were observed at elevated temperatures. For instance, the 70-CNTs@Fe₃O₄/PU sample with 15 wt% loading content at 333 K exhibits excellent MA properties including a minimum reflection loss (RL_m) of -66.9 dB and ultrabroad effective frequency bandwidth (RL ≤ -20 dB) of 9.98 GHz at the thickness of 1.58-3.37 mm. Meanwhile, great recoverability in terms of RL-fprofile was achieved in the process of thermal cooling back to 253 K. Such adjustable MA property was attributed to the well-matched impedance and dramatic attenuation ability, benefiting from the temperature-dependant electrical conductivity, abundant interfacial polarization and interior microcellular structures. Besides, the rising temperature increased the sample elongation and electrical conductivity with a slight sacrifice of maximum tensile strength. This stretchable PU skeleton with a unique assembly of CNTs and Fe₃O₄nanoparticles are expected to be promising candidates as smart absorbers for application in the harsh environments.

Carbon Fibers Embedded with Aligned Magnetic Particles for Efficient Electromagnetic Energy Absorption and Conversion

Harvesting electromagnetic (EM) energy from the environment and converting it into useful micropower is a new and ideal way to eliminate EM radiation and while providing power for microelectronic devices. The key material of this technology is broadband, ultralight, and ultrathin EM-wave-absorbing materials, whose preparation remains challenging. Herein, a high magnetic field (HMF) strategy is proposed to prepare a biomass-derived CoFe/carbon fiber (CoFe/CF) composite, in which CoFe magnetic particles are aligned in CFs, creating magnetic coupling and fast electron transmission channels. The graphitization degree of CFs is improved via the "migration catalysis" of CoFe particles under HMF. The HMF-derived CoFe/CF shows a largely broadened EM wave absorption bandwidth under ultralight and ultrathin conditions (1.5 mm). Its absorption bandwidth increases 5-10 times compared with conventional CoFe/CF that has randomly distributed CoFe particles and surpasses the reported analogues. A device model for EM energy absorption and reuse is designed based on the HMF-derived CoFe/CF membrane, which exhibits a 300% higher capability than conventional CoFe/CF membrane in converting EM energy to thermal energy. This work offers a new strategy for the design and fabrication of broadband, ultrathin, and ultralight EM wave absorption materials and demonstrates a potential conversion approach of the waste EM energy.