Optimizing Integrated-Loss Capacities via Asymmetric Electronic Environments for Highly Efficient Electromagnetic Wave Absorption.

Asymmetric electronic environments based on microscopic-scale perspective have injected infinite vitality in understanding the intrinsic mechanism of polarization loss for electromagnetic (EM) wave absorption, but still exists a significant challenge. Herein, Zn single-atoms (SAs), structural defects, and Co nanoclusters are simultaneously implanted into bimetallic metal-organic framework derivatives via the two-step dual coordination-pyrolysis process. Theoretical simulations and experimental results reveal that the electronic coupling interactions between Zn SAs and structural defects delocalize the symmetric electronic environments and generate additional dipole polarization without sacrificing conduction loss owing to the compensation of carbon nanotubes. Moreover, Co nanoclusters with large nanocurvatures induce a strong interfacial electric field, activate the superiority of heterointerfaces and promote interfacial polarization. Benefiting from the aforementioned merits, the resultant derivatives deliver an optimal reflection loss of -58.9 dB and the effective absorption bandwidth is 5.2 GHz. These findings provide an innovative insight into clarifying the microscopic loss mechanism from the asymmetric electron environments viewpoint and inspire the generalized electronic modulation engineering in optimizing EM wave absorption.

Hierarchical Co2 P/CoS2 @C@MoS2 Composites with Hollow Cavity and Multiple Phases Toward Wideband Electromagnetic Wave Absorption.

The synergistic effect of hollow cavities and multiple hetero-interfaces displays huge advantages in achieving lightweight and high-efficient electromagnetic wave absorption, but still confronts huge challenges. Herein, hierarchical Co2 P/CoS2 @C@MoS2 composites via the self-sacrificed strategy and a subsequent hydrothermal method have been successfully synthesized. Specifically, ZIF-67 cores first act as the structural template to form core-shell ZIF-67@poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) (ZIF-67@PZS) composites, which are converted into hollow Co2 P@C shells with micro-mesoporous characteristics because of the gradient structural stabilities and preferred coordination ability. The deposition of hierarchical MoS2 results in phase transition (Co2 P→Co2 P/CoS2 ), yielding the formation of hierarchical Co2 P/CoS2 @C@MoS2 composites with hollow cavities and multiple hetero-interfaces. Benefiting from the cooperative advantages of hollow structure, extra N,P,S-doped sources, lattice defects/vacancies, diverse incoherent interfaces, and hierarchical configurations, the composites deliver superior electromagnetic wave capability (-56.6 dB) and wideband absorption bandwidth (8.96 GHz) with 20 wt.% filler loading. This study provides a reliable and facile strategy for the precise construction of superior electromagnetic wave absorbents with efficient absorption attenuation.

Hierarchical Fe-Co@TiO2 with Incoherent Heterointerfaces and Gradient Magnetic Domains for Electromagnetic Wave Absorption.

Induced polarization response and integrated magnetic resonance show prosperous advantages in boosting electromagnetic wave absorption but still face huge challenges in revealing the intrinsic mechanism. In this work, we propose a self-confined strategy to construct hierarchical Fe-Co@TiO2 microrods with numerous incoherent heterointerfaces and gradient magnetic domains. The results demonstrate that the use of polyvinylpyrrolidone (PVP) coating is crucial for the subsequent deposition of Co-zeolitic imidazolate frameworks (ZIF-67), the distance of ordered arranged metal ions manipulates the size of magnetic domains, and the pyrolysis of PVP layers restricts the eutectic process of Fe-Co alloys to some extent. As a result, these introduced lattice defects, oxygen vacancies, and incoherent heterointerfaces inevitably generate a strong polarization response, and the regulated gradient magnetic domains realize integrated magnetic resonance, including macroscopic magnetic coupling, long-range magnetic diffraction, and nanoscale magnetic bridge connection, and both of the intrinsic mechanisms in dissipating electromagnetic energy are quantitatively clarified by Lorentz off-axis electron holography. Owing to the cooperative merits, the Fe-Co@TiO2 absorbents exhibit enhanced absorption intensity and strong absorption bandwidth. This study inspires us to develop a generalized strategy for manipulating the size of magnetic domains, and the integrated magnetic resonance theory provides a versatile methodology in clarifying magnetic loss mechanism.

Two-Dimensional Metal Organic Framework derived Nitrogen-doped Graphene-like Carbon Nanomesh toward Efficient Electromagnetic Wave Absorption.

Functional two-dimensional (2D) graphene-like carbon has the potential to be a good electromagnetic wave absorbing material due to its good electronic properties, but the preparation of 2D carbon via metal-organic frameworks (MOFs) derivation method is still a bottleneck. Herein, we fabricated ultrathin nitrogen-doped graphene-like carbon nanomesh (N-GN) via thermal exfoliation of 2D MOF (Zn-ZIF-L) directly. The species of the chloride salt that exfoliated Zn-ZIF-L have an effect on the nitrogen content, graphitization degree, pore size and specific surface area of N-GN. The Zn-ZIF-L derived N-GN exfoliated by KCl and LiCl simultaneously has the optimum reflection loss of -54 dB only with the thickness of 2.1 mm and the filler loading of 3 wt%. The excellent electromagnetic wave absorbing property is attributed to its favorable structure, micro-meso-macropores, N heteroatoms, abundant heterogeneous graphene-like carbon nanomesh interfaces and defects. Our simple and low-cost preparation process facilitates the large-scale production and application for electromagnetic wave absorbing material of functionalized graphene-like carbon.

Construct of CoZnO/CSP biomass-derived carbon composites with broad effective absorption bandwidth of 7.2 GHz and excellent microwave absorption performance.

Biomass-carbon materials have excellent electromagnetic wave attenuation properties, which is one of the essential factors for developing ultra-thin matched-thickness, and high-performance microwave absorption materials. This study reports a two-step procedure consisting of carbonization and subsequent in-situ growth for preparing a wrinkle-like multilayer biomass-derived composites with magnetic Co particles and ZnO particles (CoZnO/C-X). The synergistic effect of a wrinkle-like multilayer structure and Co and ZnO particles, as well as the existence of many heterogeneous interfaces in the composites structure, and efficiently creates multiple scattering and reflections, which gives the composites the strong microwave absorption properties. The minimum reflection loss value (RLmin) of CoZnO/C-X reaches - 54.90 dB with a thickness of 1.8 mm, and the effective absorption bandwidth (lower than - 10 dB) is 7.2 GHz covering from 10.8 GHz to18.0 GHz with matching thickness of 2.0 mm. Furthermore, the reasonable dielectric/magnetic losses, optimized impedance matching and enhanced polarization loss play an indispensable role among improving microwave absorption performance. Thus, this result provides a good potential method for preparation of magnetic particle/metal oxide/biomass-derived carbon microwave absorbing structural materials.

Construction of self-assembled bilayer core-shell V2O3 microspheres as absorber with superior microwave absorption performance.

The design and preparation of heterogeneous structures of dielectric materials has been the mainstream direction for the construction of superior microwave absorption materials (MAMs). We report a facile and efficient procedure combination of hydrothermal process and subsequent heat treatment for successfully prepared bilayer core-shell structure self-assembled V2O3 microspheres (BCSV). The microstructure, defects, dielectric properties and microwave absorption (MA) properties of BCSV were systematically investigated, and the effect of bilayer core-shell structure on the MA properties was discussed. By varying the heat treatment temperature, it is feasible to regulate the thickness of V2O3 bilayer and its unique structure defects, hence enhancing the attenuation and multiple polarization loss of electromagnetic waves inside the microspheres. Self-assembled V2O3 microspheres with bilayer core-shell structure exhibit high-performance MA property. The reflection loss (RL) gets to - 67.12 dB at 11.69 GHz covering the whole X-band after heat treatment at 600 °C, and the broad effective absorption bandwidth is 5.49 GHz with a thickness of 2.20 mm. The conductivity loss, multiple polarization loss and dielectric loss are ascribed to the specific bilayer core-shell structure. Thus, our work provides a good perspective on how to create vanadium oxide-based MAMs with effective absorption and broad bandwidth.

Bird-Nest-Like Multi-Interfacial MXene@SiCNWs@Co/C Hybrids with Enhanced Electromagnetic Wave Absorption.

Newly emerged two-dimensional transition metal carbides and/or nitrides (MXenes) have attracted considerable interest in the field of electromagnetic wave absorption, but their excessive conductivity and single loss mechanism limit their applicability. Herein, an MXene decorated with SiCNWs@Co/C was prepared by in situ growth and carbonization processes, followed by electrostatic self-assembly. The electromagnetic wave absorption performance of MXene@SiCNWs@Co/C with a bird-nest-like structure could be effectively regulated and optimized by changing the proportion of MXene and SiCNWs@Co/C. The prepared MXene@SiCNWs@Co/C hybrid absorbers reveal superior impedance matching, complementary dissipation mechanism, and plentiful heterointerfaces. Profiting from the synergy of abovementioned factors, the resultant MXene@SiCNWs@Co/C absorber exhibits an optimum reflection loss (RL) value of -76.5 dB at 6.36 GHz under a thickness of 3.9 mm and broad effective absorption bandwidth (EAB, RL ≤ -10 dB) of 6.2 GHz (11.8-18.0 GHz) with a thickness of only 2.0 mm, covering the entire Ku band. This work offers new insights into designing and fabricating highly efficient MXene-based electromagnetic absorbers.

Customizing Heterointerfaces in Multilevel Hollow Architecture Constructed by Magnetic Spindle Arrays Using the Polymerizing-Etching Strategy for Boosting Microwave Absorption.

Heterointerface engineering is evolving as an effective approach to tune electromagnetic functional materials, but the mechanisms of heterointerfaces on microwave absorption (MA) remain unclear. In this work, abundant electromagnetic heterointerfaces are customized in multilevel hollow architecture via a one-step synergistic polymerizing-etching strategy. Fe/Fe3 O4 @C spindle-on-tube structures are transformed from FeOOH@polydopamine precursors by a controllable reduction process. The impressive electromagnetic heterostructures are realized on the Fe/Fe3 O4 @C hollow spindle arrays and induce strong interfacial polarization. The highly dispersive Fe/Fe3 O4 nanoparticles within spindles build multi-dimension magnetic networks, which enhance the interaction with incident microwaves and reinforce magnetic loss capacity. Moreover, the hierarchically hollow structure and electromagnetic synergistic components are conducive to the impedance matching between absorbing materials and air medium. Furthermore, the mechanisms of electromagnetic heterointerfaces on the MA are systematically investigated. Accordingly, the as-prepared hierarchical Fe/Fe3 O4 @C microtubes exhibit remarkable MA performance with a maximum refection loss of -55.4 dB and an absorption bandwidth of 4.2 GHz. Therefore, in this study, the authors not only demonstrate a synergistic strategy to design multilevel hollow architecture, but also provide a fundamental guide in heterointerface engineering of highly efficient electromagnetic functional materials.

Size-Dependent Oxidation-Induced Phase Engineering for MOFs Derivatives Via Spatial Confinement Strategy Toward Enhanced Microwave Absorption.

Precisely reducing the size of metal-organic frameworks (MOFs) derivatives is an effective strategy to manipulate their phase engineering owing to size-dependent oxidation; however, the underlying relationship between the size of derivatives and phase engineering has not been clarified so far. Herein, a spatial confined growth strategy is proposed to encapsulate small-size MOFs derivatives into hollow carbon nanocages. It realizes that the hollow cavity shows a significant spatial confinement effect on the size of confined MOFs crystals and subsequently affects the dielectric polarization due to the phase hybridization with tunable coherent interfaces and heterojunctions owing to size-dependent oxidation motion, yielding to satisfied microwave attenuation with an optimal reflection loss of -50.6 dB and effective bandwidth of 6.6 GHz. Meanwhile, the effect of phase hybridization on dielectric polarization is deeply visualized, and the simulated calculation and electron holograms demonstrate that dielectric polarization is shown to be dominant dissipation mechanism in determining microwave absorption. This spatial confined growth strategy provides a versatile methodology for manipulating the size of MOFs derivatives and the understanding of size-dependent oxidation-induced phase hybridization offers a precise inspiration in optimizing dielectric polarization and microwave attenuation in theory.

A hollow CuS@Mn(OH)2 particle with double-shell structure for Ultra-wide band electromagnetic absorption.

Hollow materials have many advantages when acting as electromagnetic wave (EMW) absorber, such as excellent impedance matching properties, rich micro-interfaces and light weight. In this work, a novel hollow particle with double-shell composed with CuS and Mn(OH)2 is synthesized by coordination etching, precipitation and sulfuration using tetrakaidecahedral Cu2O as template. These hollow particles are expected to be used as improved EMW absorption property at an ultra-wide band. In this hollow particle, tetrakaidecaheral CuS acts as inner shell and Mn(OH)2 acted as outer shell, thus having rich heterogeneous interfaces which induce strong interfacial polarization. Moreover, the lower electrical conductivity and loose structure of the Mn(OH)2 shell facilitates the entry of EMW into the absorbers, and the hollow structure in this particle is beneficial to improve the impedance matching according to Maxwell-Garnett (MG) theory. Therefore, hollow CuS@Mn(OH)2 particles with double-shell exhibit excellent EMW absorption performance. The effective absorption bandwidth (reflection loss (RL) ≤ -10 dB) is 6.88 GHz (from 11.12 GHz to 18 GHz) at 2.3 mm thickness of sample.

A high-performance solid electrolyte assisted with hybrid biomaterials for lithium metal batteries.

The demand for high safety lithium batteries has led to the rapid development of solid electrolytes. However, some inherent limitations of solid polymer electrolytes (SPEs) impede them achieving commercial value. In this work, a novel polyethylene oxide (PEO)-based solid electrolyte is reported. For the first time, biomaterial-based chitosan-silica (CS) hybrid particles serve as fillers, which can interact with polymer matrix to significantly improve the electrochemical performance. The optimized polymer electrolyte exhibits a maximum ion conductivity of 1.91 × 10-4 S·cm-1 at 30 °C when the mass ratio of PEO and CS is 4:1 (PCS4). All-solid-state LiFePO4|PCS4|Li cells deliver a high coulombic efficiency and stable cycling performance, remaining an excellent capacity of more than 96.2 % after 150 cycles. Furthermore, the wide electrochemical window (5.4 V) and steady interfacial stability provide the possibility for high-voltage batteries applications. NCM811|| Li cells are assembled and display reliable charge and discharge cycle properties.

Core-shell CoFe2O4@C nanoparticles coupled with rGO for strong wideband microwave absorption.

Strong absorption and large bandwidth are two contributors to materials' absorbing performance. In this work, a series of multi-element core-shell magnetic nano-particle composite layered graphene absorbing materials CoFe2O4@C/rGO (CCr) were prepared by adjusting carbon shell thickness. The CCr at a low thickness achieved strong microwave absorption and a wide effective absorption bandwidth. Not only the core-shell structure of the magnetic nanoparticle CoFe2O4@C (CFO@C) increases the interface loss, but both the coating carbon shell and the core CoFe2O4 (CFO) are beneficial to improve impedance matching. Due to the synergistic effect of the dielectric and magnetic properties of graphene and ferrite, CCr possessed high absorption performance, and its minimum reflection loss reached (RLmin) -52.5 dB when the thickness was only 2 mm. At the same time, the effective absorption bandwidth (EAB) was 5.68 GHz when the thickness was only 1.7 mm. The chemically stable core-shell dielectric nanocomposite provided a new solution for preparing materials with excellent chemical structure and high absorbing properties.

MoS2-Decorated/Integrated Carbon Fiber: Phase Engineering Well-Regulated Microwave Absorber.

Phase engineering is an important strategy to modulate the electronic structure of molybdenum disulfide (MoS2). MoS2-based composites are usually used for the electromagnetic wave (EMW) absorber, but the effect of different phases on the EMW absorbing performance, such as 1T and 2H phase, is still not studied. In this work, micro-1T/2H MoS2 is achieved via a facile one-step hydrothermal route, in which the 1T phase is induced by the intercalation of guest molecules and ions. The EMW absorption mechanism of single MoS2 is revealed by presenting a comparative study between 1T/2H MoS2 and 2H MoS2. As a result, 1T/2H MoS2 with the matrix loading of 15% exhibits excellent microwave absorption property than 2H MoS2. Furthermore, taking the advantage of 1T/2H MoS2, a flexible EMW absorbers that ultrathin 1T/2H MoS2 grown on the carbon fiber also performs outstanding performance only with the matrix loading of 5%. This work offers necessary reference to improve microwave absorption performance by phase engineering and design a new type of flexible electromagnetic wave absorption material to apply for the portable microwave absorption electronic devices.

Ultra-broadband and covalently linked core-shell CoFe2O4@PPy nanoparticles with reduced graphene oxide for microwave absorption.

Covalent bond usually ensures a stable connection between nonmetallic atoms. However, the traditional reflux method usually requires the construction of complex instruments and equipment with tedious steps to ensure airtightness and reaction stability. In this work, an advanced method is adopted to bind core-shell CoFe2O4@PPy and rGO tightly via the aid of 2-(1H-pyrrol-1-yl)ethanamine (PyEA), dispense with a high-temperature environment or protective gas. Cobalt ferrite core and polypyrrole shell collaborate to approach suitable magnetic and conduction loss, while reduced graphene oxide usually provides a stable sheet structure for interface multiple reflections, and replenish the insufficient dielectric loss. The filled biscuit-shaped covalently bond CoFe2O4@PPy-rGO has a fantastically broad absorption bandwidth of 13.12 GHz under the thickness of 3.6 mm, together with a minimum reflection loss of -50.1 dB at 6.56 GHz, achieving both impedance matching and attenuation matching, and effectively responding to all electromagnetic waves in the X and Ku bands. Thus, the covalently bonded CoFe2O4@PPy-rGO has potential application in broadband absorption.

Magnetic porous CoNi@C derived from bamboo fiber combined with metal-organic-framework for enhanced electromagnetic wave absorption.

In order to commit to the core concept of energy saving and emission reduction, the preparation of absorbing materials with sustainable development, light weight, strong absorption and wide absorption bandwidth has become an urgent problem that should be solved. As a natural product from nature, ubiquitous bamboo is combined with metal-organic framework on its surface through a simple chemical activation method is demostrated to be an effective method to prepare a composite absorbing material with amazing electromagnetic wave absorption. The prepared bamboo fiber/CoNi alloy (CN-ABF) reaches a minimum reflection loss of -75.19 dB at 11.12 GHz when the thickness is 2.66 mm, and the corresponding bandwidth is 4.56 GHz. The prepared CN-ABF greatly enhances the multi-polarity, dielectric loss, magnetic loss and impedance matching. Sustainable absorbing materials prepared by using biomass as a dielectric carbon-based recombined magnetic metal provide a good research strategy for improving the absorbing performance of materials.

Insight into the rapid sodium storage mechanism of the fiber-like oxygen-doped hierarchical porous biomass derived hard carbon.

Biomass, as a continuously available raw material, is widely used to produce hard carbon. However, many researchers have ignored the natural special morphology of biomass and the influence of oxygen on the sodium storage performance. Here, we use the cilia of the setaria viridis as the precursor to obtain a fiber-like oxygen-doped hierarchical porous hard carbon (SVC). The sodium storage mechanism of SVC is studied by controlling the pyrolysis temperature. Studies have shown that the natural fibrous structure and vertical holes of SVC can provide channels for the rapid penetration of electrolyte. The appropriate nanocrystal size affords commodious circumstances for the insertion of Na+. More importantly, the increase in carbonization temperature will change the bonding mode of carbon and oxygen, promote the rupture of single bonds and retain the existence of double bonds, which is beneficial to the improvement of coulombic efficiency and reversible capacity. The hybrid sodium storage mechanism composed of insertion behavior and capacitance behavior promotes SVC to have higher reversible capacity (285.4 mAh g-1 at 0.05 A g-1) and excellent rate performance (90.7 mAh g-1 at 5 A g-1). This research provides some new ideas for the study of hard carbon.

CoMo-bimetallic N-doped porous carbon materials embedded with highly dispersed Pt nanoparticles as pH-universal hydrogen evolution reaction electrocatalysts.

The hydrogen evolution reaction is a key half reaction for water electrolysis and is of great significance. Pt-based nanomaterials are promising candidates for HER electrocatalysts. However, the high price of platinum and poor durability impede their practical applications. Herein, a new CoMo-bimetallic hybrid zeolite imidazolate framework is employed to load Pt nanoparticles in a highly dispersed manner as a precursor to synthesize an efficient pH-universal HER electrocatalyst (PtCoMo@NC), which displays overpotentials of 26, 51, and 66 mV at a current density of 10 mA cm-2 in acidic, basic, and neutral media, respectively. The strong synergistic effect of highly dispersed multi-type catalytic species, including cobalt, molybdenum carbide, and platinum (4.7%) promotes the catalytic activity in the HER process. Meanwhile, the aggregation of Pt nanoparticles is greatly restrained by the carbon matrix so that a brilliant long-time durability of 12 hours and a negligible current decrease in the LSV curve after 10 000 CV cycles are achieved.

High-Performance Electromagnetic Wave Absorbers Based on Two Kinds of Nickel-Based MOF-Derived Ni@C Microspheres.

Metal-organic framework (MOF)-derived composites on the microwave absorption have received extensive attention. However, which kind of organic ligand corresponding MOF derivative has better electromagnetic wave absorption performance is an urgent problem to be solved. In this work, two kinds of Ni@C derived from the Ni-based MOFs with two kinds of organic ligands (dimethylimidazole as a ligand named as Ni-ZIF and trimesic acid as a ligand named as Ni-BTC) were successfully obtained. The compositions, morphologies, and electromagnetic properties of two composites were well controlled. As a result, both kinds of Ni@C exhibited the good microwave absorption properties. Comparatively speaking, the Ni@C derived from Ni-ZIF performs better. The Ni@C-ZIF microspheres with a 40% mass filling ratio exhibited a strong reflection loss of -86.8 dB at 13.2 GHz when the matching thickness was 2.7 mm, and the corresponding effective absorption bandwidth was 7.4 GHz (4-11.4 GHz) with the thickness ranging from 1.5 to 4.0 mm. The impedance matching, multiple reflection, and interfacial polarization among Ni and C were beneficial to the enhancement of microwave attenuation, which N-doping introduced by nitrogen-containing ligands leads to excellent microwave absorption properties. Therefore, this work can give insights into understanding the absorbing mechanism as well as provide a simple and flexible paradigm for the design and synthesis of the absorber with the tunable and high-efficiency performances.

Core-Shell CoNi@Graphitic Carbon Decorated on B,N-Codoped Hollow Carbon Polyhedrons toward Lightweight and High-Efficiency Microwave Attenuation.

Lightweight and high-efficiency microwave attenuation are two major challenges in the exploration of carbon-based absorbers, which can be achieved simultaneously by manipulating their chemical composition, microstructure, or impedance matching. In this work, core-shell CoNi@graphitic carbon decorated on B,N-codoped hollow carbon polyhedrons has been constructed by a facile pyrolysis process using metal-organic frameworks as precursors. The B,N-codoped hollow carbon polyhedrons, originated from the calcination of Co-Ni-ZIF-67, are composed of carbon nanocages and BN domains, and CoNi alloy is encapsulated by graphitic carbon layers. With a filling loading of 30 wt %, the absorber exhibits a maximum RL of -62.8 dB at 7.2 GHz with 3 mm and the effective absorption bandwidth below -10 dB remarkably reaches as strong as 8 GHz when the thickness is only 2 mm. The outstanding microwave absorption performance stems from the hollow carbon polyhedrons and carbon nanocages with interior cavities, the synergistic coupling effect between the abundant B-C-N heteroatoms, the strong dipolar/interfacial polarizations, the multiple scatterings, and the improved impedance matching. This study demonstrates that the codoped strategy provides a new way for the rational design of carbon-based absorbers with lightweight and superior microwave attenuation.

Enhanced microwave-absorption with carbon-encapsulated Fe-Co particles on reduced graphene oxide nanosheets with nanoscale-holes in the basal plane.

In this study, an Fe-Co alloy is coated with carbon and decorated on a holey reduced graphene oxide nanosheet (FeCo@C/HRGO) composite. The structure is synthesized using liquid-phase reduction and hydrothermal processes followed by high-temperature calcination. The FeCo@C/HRGO composite is identified and characterized using XRD, XPS, Raman spectroscopy, TEM, and SEM. This novel composite exhibits excellent electromagnetic-wave absorption properties. The maximum reflection loss for FeCo@C/HRGO reaches -76.6 dB at 16.64 GHz with a thickness of 1.7 mm. The RL below -10 dB reaches 14.32 GHz for a thickness of 1.7-5.0 mm. This confirms that microwave absorption of FeCo@C can be substantially improved upon decoration with HRGO nanosheets.