Two Birds with One Stone: FeS2@C Yolk-Shell Composite for High-Performance Sodium-Ion Energy Storage and Electromagnetic Wave Absorption

Multifunctional carbon aerogels loaded with pea-pod-like carbon nanotubes for outstanding electromagnetic wave absorption performance

Although ordered porous carbon materials (PCMs) have shown promising potential in the field of electromagnetic wave absorption (EWA), creating multifunctional PCMs with outstanding microwave absorption performance remains a significant challenge. Herein, ordered porous carbon aerogels loaded with pea-pod-like nitrogen-doped carbon nanotubes (CNTs) were fabricated via orientation freeze-drying followed by high-temperature pyrolysis. The optimized aerogel exhibits extraordinary EWA performance with a broad effective absorption bandwidth of 7.68 GHz and exceptionally strong absorption of -91.58 dB at a low filling ratio of only 3 wt%, which is the largest absorption strength among all known aerogels to date. The exceptional EWA performance is attributed to the synergistic effect of abundant loss mechanisms resulting from a unique pod-like structure in ordered porous carbon aerogel, where nitrogen-doped CNTs encapsulate magnetic alloy nanoparticles. Optimized aerogel exhibits superior compressive elasticity, thermal insulation, and light weight, laying the groundwork for designing practical next-generation EWA materials.

Sulfur-bridged bonds enabled structure modulation and space confinement of MnS for superior sodium-ion capacitors

Manganese sulfide (MnS) is a promising converion-type anode for sodium storage, owing to the virtues of high theoretical capacity, coupled with it crustal abundance and cost-effectiveness. Nevertheless, MnS suffers from inadequate electronic conductivity, sluggish Na+ reaction kinetics and considerable volume variation during discharge/charge process, thereby impeding its rate capability and capacity retention. Herein, a novel lamellar heterostructured composite of Fe-doped MnS nanoparticles/positively charged reduced graphene oxide (Fe-MnS/PG) was synthesized to overcome these issues. The Fe-doping can accelerate the ion/electron transfer, endowing fast electrochemical kinetics of MnS. Meanwhile, the graphene space confinement with strong MnSC bond interactions can facilite the interfacial electron transfer, hamper volume expansion and aggregation of MnS nanoparticles, stabilizing the structural integrity, thus improving the Na+ storage reversibility and cyclic stability. Combining the synergistic effect of Fe-doping and space confinement with strong MnSC bond interactions, the as-produced Fe-MnS/PG anode presents a remarkable capacity of 567 mAh/g at 0.1 A/g and outstanding rate performance (192 mAh/g at 10 A/g). Meanwhile, the as-assembled sodium-ion capacitor (SIC) can yield a high energy density of 119 Wh kg-1 and a maximum power density of 17500 W kg-1, with capacity retention of 77 % at 1 A/g after 5000 cycles. This work offers a promising strategy to develop MnS-based practical SICs with high energy and long lifespan, and paves the way for fabricating advanced anode materials.

Unlocking the Potential of Iron Sulfides for Sodium-Ion Batteries by Ultrafine Pulverization

Iron sulfides have attracted tremendous research interest for the anode of sodium-ion batteries due to their high capacity and abundant resource. However, the intrinsic pulverization and aggregation of iron sulfide electrodes induced by the conversion reaction during cycling are considered destructive and undesirable, which often impedes their capacity, rate capability, and long-term cycling stability. Herein, an interesting pulverization phenomenon of ultrathin carbon-coated Fe1- xS nanoplates (Fe1- xS@C) is observed during the first discharge process of sodium-ion batteries, which leads to the formation of Fe1- xS nanoparticles with quantum size (≈5 nm) tightly embedded in the carbon matrix. Surprisingly, no discernible aggregation phenomenon can be detected in subsequent cycles. In/ex situ experiments and theoretical calculations demonstrate that ultrafine pulverization can confer several advantages, including sustaining reversible conversion reactions, reducing the adsorption energies, and diffusion energy barriers of sodium atoms, and preventing the aggregation of Fe1- xS particles by strengthening the adsorption between pulverized Fe1- xS nanoparticles and carbon. As a result, benefiting from the unique ultrafine pulverization, the Fe1- xS@C anode simultaneously exhibits high reversible capacity (610 mAh g-1 at 0.5 A g-1), superior rate capability (427.9 mAh g-1 at 20 A g-1), and ultralong cycling stability (377.9 mAh g-1 after 2500 cycles at 20 A g-1).

Microwave-Absorbing Foams with Adjustable Absorption Frequency and Structural Coloration

Microwave-absorbing materials with regulatable absorption frequency and optical camouflage hold great significance in intelligent electronic devices and advanced stealth technology. Herein, we present an innovative microwave-absorbing foam that can dynamically tune microwave absorption frequencies via a simple mechanical compression while in parallel enabling optical camouflage over broad spectral ranges by adjusting the structural colors. The vivid colors spanning different color categories generated from thin-film interference can be precisely regulated by adjusting the thickness of the conformal TiO2 coatings on Ni/melamine foam. Enhanced interfacial and defect-induced polarizations resulting from the introduction of TiO2 coating synergistically contribute to the dielectric attenuation performance. Consequently, such a foam exhibits exceptional microwave absorption capabilities, and the absorption frequency can be dynamically tuned from the S band to the Ku band by manipulating its compression ratio. Additionally, simulation calculations validate the adjustable electromagnetic wave loss behavior, offering valuable insights for the development of next-generation intelligent electromagnetic devices across diverse fields.

Atomic Valence Reversal-Induced Polarization Resonance Spurs Highly Efficient Electromagnetic Wave Absorption in α-Fe2O3@Carbon Microtubes

Variegation and complexity of polarization relaxation loss in many heterostructured materials provide available mechanisms to seek a strong electromagnetic wave (EMW) absorption performance. Here we construct a unique heterostructured compound that bonds α-Fe2O3 nanosheets of the (110) plane on carbon microtubes (CMTs). Through effective alignment between the Fermi energy level of CMTs and the conduction band position of α-Fe2O3 nanosheets at the interface, we attain substantial polarization relaxation loss via novel atomic valence reversal between Fe(III) ↔ Fe(III-) induced with periodic electron injection from conductive CMTs under EMW irradiation to give α-Fe2O3 nanosheets. Such heterostructured materials possess currently reported minimum reflection loss of -84.01 dB centered at 10.99 GHz at a thickness of 3.19 mm and an effective absorption bandwidth (reflection loss ≤ -10 dB) of 7.17 GHz (10.83-18 GHz) at 2.65 mm. This work provides an effective strategy for designing strong EMW absorbers by combining highly efficient electron injection and atomic valence reversal.

S-NiSe/HG Nanocomposites with Balanced Dielectric Loss Encapsulated in Room-Temperature Self-Healing Polyurethane for Microwave Absorption and Corrosion Protection

Exploring anticorrosion electromagnetic wave (EMW) absorbing materials in harsh conditions remains a challenge. Herein, S-NiSe/HG nanocomposites encapsulated in room-temperature self-healing polyurethane (S-NiSe/HG/SPU) were exploited as superior anticorrosion EMW absorbing materials. A dual-defect engineering collaborative Schottky interface construction endows S-NiSe/HG with a high vacancy concentration, abundant defects, and moderate conductivity. These structural merits synergistically balance dielectric loss by enhancing dipole-interface polarization loss and optimizing conduction loss. As a result, S-NiSe/HG demonstrates the optimal EMW absorption performance with a minimum reflection loss (RLmin) of -54.8 dB and an adequate absorption bandwidth (EAB) of 7.1 GHz. Besides, S-NiSe/HG/SPU combines the maze effect of S-NiSe/HG with the active repair capability of SPU, thereby providing long-term corrosion resistance for the Mg alloy. Even under corrosion for 10 days, S-NiSe/HG/SPU affords a low corrosion current density (1.3 × 10-5 A) and high charge transfer resistance (3796 Ω cm2). Overall, this work provides valuable insights for in-depth exploration of dielectric loss and development of multifunctional EMW-absorbing materials.

Highly anisotropic Fe3C microflakes constructed by solid-state phase transformation for efficient microwave absorption

Soft magnetic materials with flake geometry can provide shape anisotropy for breaking the Snoek limit, which is promising for achieving high-frequency ferromagnetic resonances and microwave absorption properties. Here, two-dimensional (2D) Fe3C microflakes with crystal orientation are obtained by solid-state phase transformation assisted by electrochemical dealloying. The shape anisotropy can be further regulated by manipulating the thickness of 2D Fe3C microflakes under different isothermally quenching temperatures. Thus, the resonant frequency is adjusted effectively from 9.47 and 11.56 GHz under isothermal quenching from 700 °C to 550 °C. The imaginary part of the complex permeability can reach 0.9 at 11.56 GHz, and the minimum reflection loss (RLmin) is -52.09 dB (15.85 GHz, 2.90 mm) with an effective absorption bandwidth (EAB≤-10 dB) of 2.55 GHz. This study provides insight into the preparation of high-frequency magnetic loss materials for obtaining high-performance microwave absorbers and achieves the preparation of functional materials from traditional structural materials.

Honeycomb-Structured MoSe2 /rGO Composites as High-Performance Anode Materials for Sodium-Ion Batteries

Sodium-ion batteries are a promising substitute for lithium batteries due to the abundant resources and low cost of sodium. Herein, honeycomb-shaped MoSe2 /reduced graphene oxide (rGO) composite materials are synthesized from graphene oxide (GO) and MoSe2 through a one-step solvothermal process. Experiments show that the 3D honeycomb structure provides excellent electrolyte penetration while alleviating the volume change during electrochemical cycling. An anode prepared with MoSe2 /rGO composites exhibits significantly improved sodium-ion storage properties, where a large reversible capacity of 215 mAh g-1 is obtained after 2700 cycles at the current density of 30.0 A g-1 or after 5900 cycles at 8.0 A g-1 . When such an anode is paired with Na3 V2 (PO4 )3 to form a full cell, a reversible specific capacity of 107.5 mAh g-1 can be retained after 1000 cycles at the current of 1.0 A g-1 . Transmission electron microscopy, X-ray photoelectron spectroscopy and in situ X-ray diffraction (XRD) characterization reveal the reversible storage reaction of Na ions in the MoSe2 /rGO composites. The significantly enhanced sodium storage capacity is attributed to the unique honeycomb microstructure and the use of ether-based electrolytes. This study illustrates that combining rGO with ether-based electrolytes has tremendous potential in constructing high-performance sodium-ion batteries.

Drawing Inspiration from Nature: Trinitarian Strategies for Designing Polyoxometalates and Metal-Organic Framework-Based Biomimetic Microhoneycomb Electromagnetic Wave-Absorbing Materials

Trinitarian designs in the morphology, components, and microstructure remain challenging for advanced electromagnetic wave absorption (EMWA) materials with light weight, strong absorption, and well-defined structure-function relationships. Herein, a series of X-doped MoS2/Cu9S5 with multilevel honeycomb structures (X-MoS2/Cu9S5 MHs, X = P, Si, Ge) were designed by space-confined growth and in situ sulfidation of a polyoxometalate-based metal-organic framework. X-MoS2/Cu9S5 MHs possess low density, high surface area, and abundant cation-cuprum and anion-sulfur double vacancies (VCu and VS) simultaneously that are unmatched by conventional EMWA materials. Also, the systematic investigation of the doping effect of various polyoxometalate heteroatoms on VCu and VS in the microhoneycomb has been conducted. Experimental results and density functional theory calculations reveal that the excellent EMWA performance (-56.21 dB) results from the synergistic effect of morphology design, component optimization, and vacancy regulation. This study not only provides an important opportunity to understand a morphology-component-microstructure strategy in electromagnetic wave absorption but also builds a noteworthy bridge between bioinspired engineering and microscale absorbers.

Structure and Defect Engineering of V3 S4-x Sex Quantum Dots Confined in a Nitrogen-Doped Carbon Framework for High-Performance Sodium-Ion Storage

Constructing quantum dot-scale metal sulfides with defects and strongly coupled with carbon is significant for advanced sodium-ion batteries (SIBs). Herein, Se substituted V3 S4 quantum dots with anionic defects confined in nitrogen-doped carbon matrix (V3 S4-x Sex /NC) are fabricated. Introducing element Se into V3 S4 crystal expands the interlayer distance of V3 S4 , and triggers anionic defects, which can facilitate Na+ diffusions and act as active sites for Na+ storage. Meanwhile, the quantum dots tightly encapsulated by conductive carbon framework improve the stability and conductivity of the electrode. Theoretical calculations also unveil that the presence of Se enhances the conductivity and Na+ adsorption ability of V3 S4-x Sex . These properties contribute to the V3 S4-x Sex /NC with high specific capacity of 447 mAh g-1 at 0.2 A g-1 , and prominent rate and cyclic performance with 504 mAh g-1 after 1000 cycles at 10 A g-1 . The sodium-ion hybrid capacitors (SIHCs) with V3 S4-x Sex /NC anode and activated carbon cathode can achieve high energy/power density (maximum 144 Wh kg-1 /5960 W kg-1 ), capacity retention ratio of 71% after 4000 cycles at 2 A g-1 . This work not only synthesizes V3 S4-x Sex /NC, but also provides a promising opportunity for designing quantum dots and utilizing defects to improve the electrochemical properties.

Boosting Conductive Loss and Magnetic Coupling Based on "Size Modulation Engineering" toward Lower-Frequency Microwave Absorption

The rational design of absorber size is a promising strategy for obtaining excellent electromagnetic wave (EMW) absorption performance. However, achieving controllable tuning of the material size through simple methods is challenging and the associated EMW attenuation mechanisms are still unclear. In this study, the sizes of metal-organic frameworks (MOFs) are successfully tailored by changing the growth time and the molar ratio of iron (Fe)/organic ligands. The lateral and vertical lengths of MOFs vary in the range of 200 nm to 2 µm and 100 nm to 1 µm, respectively. Both experiments and simulations confirm that the decrease of MOF size favors the formation of more conductive networks, which is beneficial for improving the conductivity loss. Meanwhile, the micromagnetic simulation reveals that the magnetic coupling can be effectively enhanced by the decrease of MOF size, which is conducive to the improvement of magnetic loss, especially in low-frequency range. The reflection loss of Fe-based MOFs with optimized size reaches -46.4 dB at 6.2 GHz with an effective absorption bandwidth of 3.1 GHz. This work illustrates the important role of size effect in EMW dissipation and provides an effective strategy for enhancing the low-frequency EMW absorption performance.

Multi-interfacial engineering in the hierarchical self-assembled micro-nano dielectric aerogel for wide-band absorption and low infrared emissivity

Radar-infrared (IR) compatible stealth can satisfy the characteristics of excellent electromagnetic wave attenuation property and low infrared emissivity. However, concurrently satisfying these demands is still a great challenge at present. Herein, multi-interfacial engineering strategy was proposed for the preparation of radar-IR compatible stealth materials. ZnO has a high electron binding energy and a large band gap at room temperature, and doping with sulphide can increase the concentration of unconstrained carriers. Therefore, bimetallic sulphide aerogels loaded with ZnO were prepared by means of carbonization and vulcanization, combined with freeze-drying method. When the filling ratio is 20 %, an absorption bandwidth (fe) of 6.62 GHz at a matching thickness of 2.0 mm and a reduction in IR emissivity from 0.920 to 0.539 in the 8-14 μm band are achieved. This work provides a guidance to design and synthesize high-performance absorbers by multi-interfacial engineering for IR-radar compatible stealth application.

In-Situ Fabrication of Sustainable-N-Doped-Carbon-Nanotube-Encapsulated CoNi Heterogenous Nanocomposites for High-Efficiency Electromagnetic Wave Absorption

Developing carbon encapsulated magnetic composites with rational design of microstructure for achieving high-performance electromagnetic wave (EMW) absorption in a facile, sustainable, and energy-efficiency approach is highly demanded yet remains challenging. Here, a type of N-doped carbon nanotube (CNT) encapsulated CoNi alloy nanocomposites with diverse heterostructures are synthesized via the facile, sustainable autocatalytic pyrolysis of porous CoNi-layered double hydroxide/melamine. Specifically, the formation mechanism of the encapsulated structure and the effects of heterogenous microstructure and composition on the EMW absorption performance are ascertained. With the presence of melamine, CoNi alloy emerges its autocatalysis effect to generate N-doped CNTs, leading to unique heterostructure and high oxidation stability. The abundant heterogeneous interfaces induce strong interfacial polarization to EMWs and optimize impedance matching characteristic. Combined with the inherent high conductive and magnetic loss capabilities, the nanocomposites accomplish a high-efficiency EMW absorption performance even at a low filling ratio. The minimum reflection loss of -84.0 dB at the thickness of 3.2 mm and a maximum effective bandwidth of 4.3 GHz are obtained, comparable to the best EMW absorbers. Integrated with the facile, controllable, and sustainable preparation approach of the heterogenous nanocomposites, the work shows a great promise of the nanocarbon encapsulation protocol for achieving lightweight, high-performance EMW absorption materials.

Synthesis of CuCo2S4@Expanded Graphite with crystal/amorphous heterointerface and defects for electromagnetic wave absorption

The remarkable advantages of heterointerface and defect engineering and their unique electromagnetic characteristics inject infinite vitality into the design of advanced carbon-matrix electromagnetic wave absorbers. However, understanding the interface and dipole effects based on microscopic and macroscopic perspectives, rather than semi-empirical rules, can facilitate the design of heterointerfaces and defects to adjust the impedance matching and electromagnetic wave absorption of the material, which is currently lacking. Herein, CuCo2S4@Expanded Graphite heterostructure with multiple heterointerfaces and cation defects are reported, and the morphology, interfaces and defects of component are regulated by varying the concentration of metal ions. The results show that the 3D flower-honeycomb morphology, the crystal-crystal/amorphous heterointerfaces and the abundant cation defects can effectively adjust the conductive and polarization losses, achieve the impedance matching balance of carbon materials, and improve the absorption of electromagnetic wave. For the sample CEG-6, the effective absorption of Ku band with RLmin of -72.28 dB and effective absorption bandwidth of 4.14 GHz is realized at 1.4 mm, while the filler loading is only 7.0 wt. %. This article reports on the establishment of potential relationship between crystal-crystal/amorphous heterointerfaces, cation defects, and the impedance matching of carbon materials.

In-situ catalytic mechanism coupling quantum dot effect for achieving high-performance sulfide anode in potassium-ion batteries

Though numerous framework structures have been constructed to strengthen the reaction kinetics and durability, the inevitable generation of polysulfide dissolution during conversion-process can cause irreparable destruction to ion-channel and crystal structure integrality, which has become a huge obstacle to the application of metal-sulfide in potassium-ion batteries. Herein, the quantum dot structure with catalytic conversion capability is synchronously introduced into the design of FeS₂ anode materials to heighten its K⁺-storage performance. The constructed quantum dot structure anchored by the graphene with space-confinement effect can shorten the ion diffusion path and enlarge the active area, thus accelerating the K⁺-ions transmission kinetics and absorption action, respectively. The intermediate phase of formed Fe-nanoclusters possesses high-active catalysis ability, which can effectively suppress the polysulfide shuttle combined with the enhanced absorption effect, fully guaranteeing the structure stability and cycling reversibility. Predictably, the fabricated quantum dot FeS₂ can express a prominent advantage in rapid potassiation/depotassiation processes (518.1 mAh g^-1, 10 A g^-1) and a superior cycling lifespan with gratifying reversible capacity at superhigh rate (177.7 mAh g^-1, 9000 cycles, 5 A g^-1). Therefore, engineering quantum dot structure with self-induced catalysis action for detrimental polysulfide is an achievable strategy to implement high-performance sulfide anode materials for K-ions accommodation.

2D-2D heterostructure of ionic liquid-exfoliated MoS2/MXene as lithium polysulfide barrier for Li-S batteries

Suppressing the dissolution and shuttling of lithium polysulfides (LiPSs) in electrolytes in lithium-sulfur batteries (LSBs) is the focus of researchers. Herein, functional liquid phase exfoliated MoS₂ and MXene (IL-MoS₂/MX) interlayer is proposed as the separator of LSBs. The unique alternating intercalation structure of the IL-MoS₂/MX interlayer provides a channel for ion transport while achieving uniform Li⁺ deposition on the anode side. Moreover, IL-MoS₂ achieves physical and chemical anchoring to LiPSs and lowers the energy barrier for battery reactions. As a result, the separator in the coin cell delivers an initial capacity of 764.4 mAh·g^-1 at 1C and high retention of 58.7 % after 700 cycles, with a decay only 0.059 % per cycle. Simultaneously, the excellent stability is also verified under varying current densities. Beyond that, ionic conductivity and lithium-ion migration number are adopted to confirm unique ion transport channels and uniform deposition of lithium. X-ray photoelectron spectroscopy, S₈ and Li₂S decomposition and nucleation energy barrier analysis are performed to verify the adsorption and catalytic conversion mechanisms. The convenient preparation and excellent performance of IL-MoS₂/MX provide a design strategy for functionalized interlayers for LSBs, and the possibility for commercialization.

Carbon nanotubes encapsulating FeS2 micropolyhedrons as an anode electrocatalyst for improving the power generation of microbial fuel cells

The low power density originating from poor electroactive bacteria (EAB) adhesion and sluggish extracellular electron transfer (EET) at the anode interface, is a major impediment preventing the practical implementation of microbial fuel cells (MFCs). Tailoring the surface properties of anodes is an effective and powerful strategy for addressing this issue. In this study, we successfully fabricated an efficient anode electrocatalyst, consisting of carbon nanotubes encapsulating iron disulfide (FeS2@CNT) micropolyhedrons, using simple hydrothermal and freeze-drying methods, which not only strengthened the anode interaction with EAB but also promoted the EET process at the anode interface. As expected, the MFCs with a FeS2@CNT anode yielded an outstanding power density of 1914 mWm-2 at a current density of 4350 mA m-2, which significantly exceeded those of pure CNT (1096.2mW m-2, 2703.3 mA m-2) and carbon cloth (426.8mWm-2, 965.6 mA m-2) anodes. The high-power output can be attributed to the synergistic effect between FeS2 and CNTs, endowing the anode with biocompatibility for biofilm adhesion and colonization, nutrient diffusion, and the presence of abundant Fe and S active sites for EET mediation. Owing to the low cost, facile fabrication process, and excellent electrocatalytic performance toward the redox reactions in biofilms, the synthesized FeS2@CNT electrocatalyst is a promising material for high-performance and cost-effective MFCs with commercial applications.

Electrochemically Controllable Synthesis of Low-Valence Titanium Sulfides for Advanced Sodium Ion Batteries with Ultralong Cycle Life in a Wide Potential Window

Low-valence titanium sulfides (LVTS) have metal-like electrical conductivities and a strong polysulfide binding abilities, which are promising anodes for sodium ion batteries with high capacities and long cycle lifes. However, it is difficult for traditional synthesis methods to synthesize LVTS without impurities. The electric field regulation method possesses the advantages of flexibility and high efficiency, achieving accurate control of the metal reduction process by adjusting the electrolysis potential and reaction time. In this work, we synthesized a series of LVTS (TiS and Ti₂S) using electric field control methods and investigated their electrochemical behaviors as sodium storage anodes for the first time. Compared with traditional TiS₂, LVTS display remarkable Na storage properties under the condition of complete electrochemical conversion at 0.005-3 V. Especially for TiS, it demonstrates a high capacity of 409 mAh g^-1 at 1 A g^-1 and inspiring cyclic stability over 6000 cycles. The large number of vacancies in the crystal structure can chemically anchor polysulfides and alleviate their dissolution in the electrolyte, resulting in superior long-term cyclic stability. The high intrinsic conductivity of LVTS is in favor of rapid transfer of electrons and promotes the fast conversion of polysulfides to sodium sulfides, thus realizing high reversible capacities. Moreover, with its fast Na⁺ transport kinetics, the as-prepared TiS demonstrates an impressive rate performance of 321 mAh g^-1 at 15 A g^-1. Overall, the electric field regulation method is flexible and efficient, which provides a new route for the preparation of high-performance electrode materials. Moreover, nonstoichiometric metal compounds possess abundant active sites and rapid electron transport kinetics, which provide a new choice for promising sodium storage materials in large-scale energy storage applications.

Achieving Ultrahigh-Rate and Low-Temperature Sodium Storage of FePS3 via In Situ Construction of Graphitized Porous N-Doped Carbon

Sodium-ion batteries (SIBs) have become an important supplementation to lithium-ion batteries. Unfortunately, the low capacity and inferior low-temperature performance of traditional hard carbon led to limited energy density and a range of applications of SIBs. Herein, we present high-performance SIBs via embedding FePS₃ in graphitized porous N-doped carbon (FPS/GPNC) using coordination polymerization reaction. Such unique graphitized pores are in situ-constructed by the self-aggregation of Fe nanoparticles with high surface energy at high temperatures, which affords a three-dimensional open channel and a graphitized conductive network for fast transportation of Na⁺ and electrons. Moreover, an ingenious buffer barrier composed of graphitized pores is constructed for FePS₃ to withstand volume fluctuation during cycling. Consequently, a superior capacity of 354.2 mAh g^-1 is delivered even when the rate increases to 50 A g^-1. The impressing cycling lifespan up to 4700 cycles is achieved at 30 A g^-1 with excellent retention of 84.4%. Interestingly, the low-temperature performance (-20 °C) of FePS₃ is explored for the first time, and excellent stability (502.6 mAh g^-1 maintained after 100 cycles at 0.1 A g^-1) is obtained, indicating huge potential of practical application. This work provides insights into designing high-rate, high-capacity, and low-temperature SIBs.

Innovative Materials for Energy Storage and Conversion

The metal chalcogenides (MCs) for sodium-ion batteries (SIBs) have gained increasing attention owing to their low cost and high theoretical capacity. However, the poor electrochemical stability and slow kinetic behaviors hinder its practical application as anodes for SIBs. Hence, various strategies have been used to solve the above problems, such as dimensions reduction, composition formation, doping functionalization, morphology control, coating encapsulation, electrolyte modification, etc. In this work, the recent progress of MCs as electrodes for SIBs has been comprehensively reviewed. Moreover, the summarization of metal chalcogenides contains the synthesis methods, modification strategies and corresponding basic reaction mechanisms of MCs with layered and non-layered structures. Finally, the challenges, potential solutions and future prospects of metal chalcogenides as SIBs anode materials are also proposed.

Dimensional Design and Core-Shell Engineering of Nanomaterials for Electromagnetic Wave Absorption

Electromagnetic (EM) wave absorption materials possess exceptionally high EM energy loss efficiency. With vigorous developments in nanotechnology, such materials have exhibited numerous advanced EM functions, including radiation prevention and antiradar stealth. To achieve improved EM performance and multifunctionality, the elaborate control of microstructures has become an attractive research direction. By designing them as core-shell structures with different dimensions, the combined effects, such as interfacial polarization, conduction networks, magnetic coupling, and magnetic-dielectric synergy, can significantly enhance the EM wave absorption performance. Herein, the advances in low-dimensional core-shell EM wave absorption materials are outlined and a selection of the most remarkable examples is discussed. The derived key information regarding dimensional design, structural engineering, performance, and structure-function relationship are comprehensively summarized. Moreover, the investigation of the cutting-edge mechanisms is given particular attention. Additional applications, such as oxidation resistance and self-cleaning functions, are also introduced. Finally, insight into what may be expected from this rapidly expanding field and future challenges are presented.

Facile fabrication of metal-organic framework derived Fe/Fe3O4/FeN/N-doped carbon composites coated with PPy for superior microwave absorption

At present, the magnetic metal/carbon composites have been widely explored for microwave absorption (MA), which effectively integrate the characteristics of magnetic and dielectric materials. As a typical material, metal-organic framework (MOF) shows tremendous potential as a precursor or template. However, its development is limited by the inferior impedance matching. Herein, a novel rod-like Fe/Fe₃O₄/FeN/N-doped carbon (FON/NC) composite was synthesized via dual-ligand strategy and following calcination. The outer polypyrrole (PPy) shell, obtained by a facile polymerization method, effectively optimized the impedance matching and observably enhanced the MA capacity. Both the multi-component loss mechanism and unique porous core-shell structures of MOF-derived composites were beneficial for microwave attenuation. The effects of filler loadings (20 wt%, 25 wt%, 30 wt% and 35 wt%) on electromagnetic (EM) properties of FON/NC@PPy composites were discussed. Remarkably, as-obtained composites exhibited a minimum reflection loss (RL) value of -60.08 dB at the layer thickness of merely 1.44 mm and the widest effective absorption bandwidth (EAB, RL ≤ -10 dB) of 5.06 GHz at 1.64 mm with 30 wt% filler loading. This work provides a great reference for designing MOF-derived absorbers with high MA performance.

Surface modification of helical carbon nanocoil (CNC) with N-doped and Co-anchored carbon layer for efficient microwave absorption

Surface modification and composition control for nanomaterials are effective strategies for designing high-performance microwave absorbing materials (MWAMs). Herein, we have successfully fabricated Co-anchored and N-doped carbon layers on the surfaces of helical carbon nanocoils (CNCs) by wet chemical and pyrolysis methods, denoted as Co@N-Carbon/CNCs. It is found that pure CNCs show a very good microwave absorption performance under a filling ratio of only 6%, which is attributed to the uniformly dispersed conductive network and the cross polarization induced by the unique chiral and spiral morphology. The coating of N-doped carbon layers on CNCs further enriches polarization losses and the uniform anchoring of Co nanoparticles in these layers generates magnetic losses, which enhance the absorption ability and improve the low frequency performance. As compared with the pure CNCs-filling samples, the optimized Co@N-Carbon/CNCs-2.4 enhances the absorption capacity in the lower frequency range under the same thickness, and realizes the decreased thickness from 3.2 to 2.8 mm in the same X band, as well as the decreased thickness from 2.2 to 1.9 mm in the Ku band. Resultantly, a specific effective absorption wave value of 22 GHz g^-1 mm^-1 has been achieved, which enlightens the synthesis of ultrathin and light high-performance MWAMs.

Ultrafast and Ultrastable Heteroarchitectured Porous Nanocube Anode Composed of CuS/FeS2 Embedded in Nitrogen-Doped Carbon for Use in Sodium-Ion Batteries

The enhancement of the structural stability of conversion-based metal sulfides at high current densities remains a major challenge in realizing the practical application of sodium-ion batteries (SIBs). The instability of metal sulfides is caused by the large volume variation and sluggish reaction kinetics upon sodiation/desodiation. To overcome this, herein, a heterostructured nanocube anode composed of CuS/FeS₂ embedded in nitrogen-doped carbon (CuS/FeS₂ @NC) is synthesized. Size- and shape-controlled porous carbon nanocubes containing metallic nanoparticles are synthesized by the two-step pyrolysis of a bimetallic Prussian blue analog (PBA) precursor. The simple sulfurization-induced formation of highly conductive CuS along with FeS₂ facilitates sodium-ion diffusion and enhances the redox reversibility upon cycling. The mesoporous carbon structure provides excellent electrolyte impregnation, efficient charge transport pathways, and good volume expansion buffering. The CuS/FeS₂ @NC nanocube anode exhibits excellent sodium storage characteristics including high desodiation capacity (608 mAh g^-1 at 0.2 A g^-1 ), remarkable long-term cycle life (99.1% capacity retention after 300 cycles at 5 A g^-1 ), and good rate capability up to 5 A g^-1 . The simple, facile synthetic route combined with the rational design of bimetallic PBA nanostructures can be widely utilized in the development of conversion-based metal sulfides and other high-capacity anode materials for high-performance SIBs.

An outstanding role of novel virus-like heterojunction nanosphere BOCO@Ag as high performance antibacterial activity agent

The development of highly efficient photonic nanomaterials with synergistic biological effects is critical and challenging task for public hygiene health well-being and has attracted extensive interest. In this study, a type of near-infrared (NIR) driven, virus-like heterojunction was first developed for synergistic biological application. The Ag-coated Bi₂CO₅ nanomaterial (BOCO@Ag) demonstrated good biocompatibility, low cytotoxicity, high antibacterial activity and excellent light utilization stability. The synthesized BOCO@Ag performed a potential high photothermal conversion (efficiency~46.81%) to generate high temperatures when irradiated with near-infrared light illumination. As expected, compared to single Ag+ disinfection, BOCO@Ag can exhibit better antibacterial performance when combined with photothermal energy and released Ag+ . These results suggest that BOCO@Ag can be a promising photo-activate antimicrobial candidate and provide security for humans health and the environment treatment.

Synthetically Produced Isocubanite as an Anode Material for Sodium-Ion Batteries: Understanding the Reaction Mechanism During Sodium Uptake and Release

Bulk isocubanite (CuFe₂S₃) was synthesized via a multistep high-temperature synthesis and was investigated as an anode material for sodium-ion batteries. CuFe₂S₃ exhibits an excellent electrochemical performance with a capacity retention of 422 mA h g^-1 for more than 1000 cycles at a current rate of 0.5 A g^-1 (0.85 C). The complex reaction mechanism of the first cycle was investigated via PXRD and X-ray absorption spectroscopy. At the early stages of Na uptake, CuFe₂S₃ is converted to form crystalline CuFeS₂ and nanocrystalline NaFe_1.5S₂ simultaneously. By increasing the Na content, Cu⁺ is reduced to nanocrystalline Cu, followed by the reduction of Fe²⁺ to amorphous Fe⁰ while reflections of nanocrystalline Na₂S appear. During charging up to -5 Na/f.u., the intermediate NaFe_1.5S₂ appears again, which transforms in the last step of charging to a new unknown phase. This unknown phase together with NaFe_1.5S₂ plays a key role in the mechanism for the following cycles, evidenced by the PXRD investigation of the second cycle. Even after 400 cycles, the occurrence of nanocrystalline phases made it possible to gain insights into the alteration of the mechanism, which shows that Cu_xS phases play an important role in the region of constant specific capacity.

Enhancing the Electrochemical Performance of Sodium-Ion Batteries by Building Optimized NiS2 /NiSe2 Heterostructures

NiS_1.23 Se_0.77 nanosheets closely attached to the internal surface of hollow mesoporous carbon sphere (HMCS) to form a NiS_1.23 Se_0.77 nanosheets embedded in HMCS (NSSNs@HMCS) composite as the anode of sodium ion batteries (SIBs) is reported by a facile synthesis route. The anode exhibits a superior reversible capacity (520 mAh g^-1 at 0.1 A g^-1 )_, impressive coulombic efficiency (CE) of up to 95.3%, a high rate capacity (353 mAh g^-1 at 5.0 A g^-1 ), excellent capacity retention at high current density (95.6%), and high initial coulombic efficiency (ICE) (95.1%). Firstly, the highest ICE for NiS₂ /NiSe₂ -based anode can be ascribed to ultrathin layered structure of NiS_1.23 Se_0.77 nanosheet and highly efficient electron transfer between the active material and HMCS. Secondly, the optimized NiS₂ /NiSe₂ heterostructure at the nanoscale of the inside HMCS is formed after the first discharge/charge cycles, which can provide rich heterojunction interfaces/boundaries of sulfide/selenides to offer faster Na⁺ pathways, decrease the Na⁺ diffusion barriers, increase electronic conductivity, and limit the dissolution of polysulfides or polyselenides in the electrolyte. Finally, the hollow structure of the HMCS accommodates the volume expansion, prevents the pulverization and aggregation issues of composite materials, which can also promote outstanding electrochemical performance.

Iron sulphide rice grain nanostructures as potential electrocatalysts for an improved oxygen evolution reaction

Iron based chalcogenides are considered a promising group of electro-active materials for various electrochemical technologies. Herein we demonstrate a facile fabrication of various iron sulphide (FeS) nanostructures, including rice grains (RGS)-, nanoflowers (NFS)- and nanoparticles (NPS)-like surface morphologies via electrochemical, solvothermal and chemical strategies, respectively. The as-developed FeS nanostructures have been employed as electrocatalysts for the oxygen evolution reaction (OER) in an alkaline electrolyte. Among other FeS nanostructures, FeS rice grains (FeS-RGS) exhibited an outstanding OER activity with a low onset potential (∼1.37 V), low overpotential (∼0.20 V), small Tafel slope (∼54.2 mV dec^-1), high mass activity (∼5.4 A g^-1), and high durability, outperforming the commercial state-of-the-art RuO₂ catalyst. The high-performance OER activity of the FeS-RGS is associated not only to the synergistic effect of Fe and S, but also to the direct growth (binder-free) and edges of rice grain structures, offering a large number of electrochemical active sites and ensuring fast-diffusion of OH^- ions of the nanostructures. The present one-step, low-cost and highly scalable preparation of FeS-RGS nanostructures provides new possibilities of morphology and synthetic methodology dependence of OER electrocatalysts for effective hydrogen production.

Bimetallic Sulfide SnS2/FeS2 Nanosheets as High-Performance Anode Materials for Sodium-Ion Batteries

Transition-metal sulfide SnS₂ has aroused wide concern due to its high capacity and nanosheet structure, making it an attractive choice as the anode material in sodium-ion batteries. However, the large volume expansion and poor conductivity of SnS₂ lead to inferior cycle stability as well as rate performance. In this work, FeS₂ was in situ introduced to synchronously grow with SnS₂ on rGO to prepare a heterojunction bimetallic sulfide nanosheet SnS₂/FeS₂/rGO composite. The composition and distinctive structure facilitate the rapid diffusion of Na⁺ and improve the charge transfer at the heterogeneous interface, providing sufficient space for volume expansion and improving anode materials' structural stability. SnS₂/FeS₂/rGO bimetallic sulfide electrode boasts a capacity of 768.3 mA h g^-1 at the current density of 0.1 A g^-1, and 541.2 mA h g^-1 at the current density of 1 A g^-1 in sodium-ion batteries, which is superior to that of either single metal sulfide SnS₂ or FeS₂. TDOS calculation further confirms that the binding of FeS₂/SnS₂-Na is more stable than FeS₂ and SnS₂ alone. The superior electrochemical performance of the SnS₂/FeS₂/rGO composite material makes it a promising candidate for sodium storage.

Electrolyte/Structure-Dependent Cocktail Mediation Enabling High-Rate/Low-Plateau Metal Sulfide Anodes for Sodium Storage

As promising anodes for sodium-ion batteries, metal sulfides ubiquitously suffer from low-rate and high-plateau issues, greatly hindering their application in full-cells. Herein, exemplifying carbon nanotubes (CNTs)-stringed metal sulfides superstructure (CSC) assembled by nano-dispersed SnS₂ and CoS₂ phases, cocktail mediation effect similar to that of high-entropy materials is initially studied in ether-based electrolyte to solve the challenges. The high nano-dispersity of metal sulfides in CSC anode underlies the cocktail-like mediation effect, enabling the circumvention of intrinsic drawbacks of different metal sulfides. By utilizing ether-based electrolyte, the reversibility of metal sulfides is greatly improved, sustaining a long-life effectivity of cocktail-like mediation. As such, CSC effectively overcomes low-rate flaw of SnS₂ and high-plateau demerit of CoS₂, simultaneously realizes a high rate and a low plateau. In half-cells, CSC delivers an ultrahigh-rate capability of 327.6 mAh g^-1_anode at 20 A g^-1, far outperforming those of monometallic sulfides (SnS₂, CoS₂) and their mixtures. Compared with CoS₂ phase and SnS₂/CoS₂ mixture, CSC shows remarkably lowered average charge voltage up to ca. 0.62 V. As-assembled CSC//Na_1.5VPO_4.8F_0.7 full-cell shows a good rate capability (0.05 ~ 1.0 A g^-1, 120.3 mAh g^-1_electrode at 0.05 A g^-1) and a high average discharge voltage up to 2.57 V, comparable to full-cells with alloy-type anodes. Kinetics analysis verifies that the cocktail-like mediation effect largely boosts the charge transfer and ionic diffusion in CSC, compared with single phase and mixed phases. Further mechanism study reveals that alternative and complementary electrochemical processes between nano-dispersed SnS₂ and CoS₂ phases are responsible for the lowered charge voltage of CSC. This electrolyte/structure-dependent cocktail-like mediation effect effectively enhances the practicability of metal sulfide anodes, which will boost the development of high-rate/-voltage sodium-ion full batteries.

Reacquainting the Electrochemical Conversion Mechanism of FeS2 Sodium-Ion Batteries by Operando Magnetometry

In spite of the excellent electrochemical performance in lithium-ion batteries (LIBs), transition-metal compounds usually show inferior capacity and cyclability in sodium-ion batteries (SIBs), implying different reaction schemes between these two types of systems. Herein, coupling operando magnetometry with electrochemical measurement, we peformed a comprehensive investigation on the intrinsic relationship between the ion-embedding mechanisms and the electrochemical properties of the typical FeS₂/Na (Li) cells. Operando magnetometry together with ex-situ transmission electron microscopy (TEM) measurement reveal that only part of FeS₂ is involved in the conversion reaction process, while the unreactive parts form "inactive cores" that lead to the low capacity. Through quantification with Langevin fitting, we further show that the size of the iron grains produced by the conversion reaction are much smaller in SIBs than that in LIBs, which may lead to more serious pulverization, thereby resulting in worse cycle performance. The underlying reason for the above two above phenomena in SIBs is the sluggish kinetics caused by the larger Na-ion radius. Our work paves a new way for the investigation of novel SIB materials with high capacity and long durability.

Strategies for Polysulfide Immobilization in Sulfur Cathodes for Room-Temperature Sodium-Sulfur Batteries

Room-temperature sodium-sulfur batteries are one of the most attractive energy storage systems due to their low cost and ultrahigh energy density (2600 W h kg^-1 ). During the charge/discharge process, the sulfur can react with sodium via a multistep redox reaction to obtain a high specific capacity (1675 mA h g^-1 ). However, these batteries face the difficult challenge of the "shuttle effect," which hinders their practical application. Many strategies have been employed to address this issue on sulfur electrodes, such as intact physical confinement, chemical inhibition, and electrocatalysis. In this review, the mechanisms of the abovementioned strategies are summarized, the remaining issues are clarified, and research directions are proposed for developing advanced sodium-sulfur batteries.

C/MnO@void@C with Triple Balances for Superior Microwave Absorption Performance

It is very promising and challenging to construct a yolk-shell structure with highly efficient microwave absorption (MA) performance through a simple fabrication process. Here, a novel C/MnO@void@C (MCC) yolk-shell structure has been successfully synthesized by one-step calcination without additional processing. The as-obtained MCC composites with tunable crystallinity degrees and hollowness can be obtained by treatment at various temperatures. The MCC composites treated at 700 °C (MCC-700) show an impressive MA performance, and the optimal reflection loss of -53.2 dB and an effective absorption bandwidth of 5.4 GHz can be obtained. This excellent performance results from multiple balance mechanisms. First, the regulated permittivity of MCC-700 due to proper crystallinity and hollowness is beneficial for the balance between dielectric loss (tan δ_ε) and impedance match (Z_im). Second, the optimal balance between the increasing polarization range and decreasing polarization intensity can be achieved, which is favorable for the improvement of the MA performance. Third, the multicore yolk-shell structure of MCC-700 is conducive to multiple scattering and continuous energy dissipation. Thus, our new findings provide a rational way for the utilization of yolk-shell structural manganese-based materials.

Carbon-Based MOF Derivatives: Emerging Efficient Electromagnetic Wave Absorption Agents

To tackle the aggravating electromagnetic wave (EMW) pollution issues, high-efficiency EMW absorption materials are urgently explored. Metal-organic framework (MOF) derivatives have been intensively investigated for EMW absorption due to the distinctive components and structures, which is expected to satisfy diverse application requirements. The extensive developments on MOF derivatives demonstrate its significantly important role in this research area. Particularly, MOF derivatives deliver huge performance superiorities in light weight, broad bandwidth, and robust loss capacity, which are attributed to the outstanding impedance matching, multiple attenuation mechanisms, and destructive interference effect. Herein, we summarized the relevant theories and evaluation methods, and categorized the state-of-the-art research progresses on MOF derivatives in EMW absorption field. In spite of lots of challenges to face, MOF derivatives have illuminated infinite potentials for further development as EMW absorption materials.

Fabrication of one-dimensional ZnFe2O4@carbon@MoS2/FeS2 composites as electromagnetic wave absorber

In this work, one-dimensional (1D) ZnFe₂O₄@carbon@MoS₂/FeS₂ composites were synthesized by hydrothermal method, magnetic-field-induced distillation-precipitation polymerization and high-temperature carbonization. The structure, morphology, composition, magnetic performance and electromagnetic (EM) wave absorbing properties of the composites were systematically studied. The composites show strong microwave absorption (MA) capacity with a minimum reflection loss (RL_min) value of -52.5 dB at 13.2 GHz, and have an effective absorption frequency range of 10.10-15.08 GHz with a bandwidth of 4.98 GHz when the thickness is 2.23 mm. It is expected that as-synthesized 1D ZnFe₂O₄@carbon@MoS₂/FeS₂ composites can be a promising EM wave absorption material.

Realizing Fast Charge Diffusion in Oriented Iron Carbodiimide Structure for High-Rate Sodium-Ion Storage Performance

Iron carbodiimide (FeNCN) belongs to a type of metal compounds with a more covalent bonding structure compared to common transition metal oxides. It could provide possibilities for various structural designs with improved charge-transfer kinetics in battery systems. Moreover, these possibilities are still highly expected for promoting enhancement in rate performance of sodium (Na)-ion battery. Herein, oriented FeNCN crystallites were grown on the carbon-based substrate with exposed {010} faces along the [001] direction (O-FeNCN/S). It provides a high Na-ion storage capacity with excellent rate capability (680 mAh g^-1 at 0.2 A g^-1 and 360 mAh g^-1 at 20 A g^-1), presenting rapid charge-transfer kinetics with high contribution of pseudocapacitance during a typical conversion reaction. This high rate performance is attributed to the oriented morphology of FeNCN crystallites. Its orientation along [001] maintains preferred Na-ion diffusion along the two directions in the entire morphology of O-FeNCN/S, supporting fast Na-ion storage kinetics during the charge/discharge process. This study could provide ideas toward the understanding of the rational structural design of metal carbodiimides for attaining high electrochemical performance in future.

Synthesis and microwave absorption properties of coralloid core-shell structure NiS/Ni3S4@PPy@MoS2 nanowires

Herein, coralloid core-shell structure NiS/Ni₃S₄@PPy@MoS₂ nanowires were elaborately designed and successfully synthesized through a three-step route to obtain exceptional microwave absorption (MA) properties. Ni nanowires were first fabricated, and then used as the substrate to be coated with a layer of PPy. Ni chalcogenides were obtained by using Ni nanowire as sacrificial templates while growing MoS₂ nanorods by hydrothermal method. Both the one-dimensional (1D) core-shell structure and the coralloid surface generated by MoS₂ nanorods were beneficial for the attenuation of microwaves. After investigating the electromagnetic properties of different loading content absorbers (30 wt.%, 40 wt.% and 50 wt.%), it is found that the 50 wt.% loading absorber has the optimal MA performance. The minimum reflection loss (RL_min) value can reach -51.29 dB at 10.1 GHz with a thickness of 2.29 mm, and the corresponding effective absorption bandwidth (EAB, RL < -10 dB) can be up to 3.24 GHz. This research provides a reference for exploiting novel high-efficient 1D absorbers in the field of MA.

Fe7Se8 encapsulated in N-doped carbon nanofibers as a stable anode material for sodium ion batteries

Transition metal chalcogenides especially Fe-based selenides for sodium storage have the advantages of high electric conductivity, low cost, abundant active sites, and high theoretical capacity. Herein, we proposed a facile synthesis of Fe₇Se₈ embedded in carbon nanofibers (denoted as Fe₇Se₈-NCFs). The Fe₇Se₈-NCFs with a 1D electron transfer network can facilitate Na⁺ transportation to ensure fast reaction kinetics. Moreover, Fe₇Se₈ encapsulated in carbon nanofibers, Fe₇Se₈-NCFs, can effectively adapt the volume variation to keep structural integrity during a continuous Na⁺ insertion and extraction process. As a result, Fe₇Se₈-NCFs present improved rate performance and remarkable cycling stability for sodium storage. The Fe₇Se₈-NCFs exhibit practical feasibility with a reasonable specific capacity of 109 mA h g^-1 after 200 cycles and a favorable rate capability of 136 mA h g^-1 at a high rate of 2 A g^-1 when coupled with Na₃V₂(PO₄)₃ to assemble full sodium ion batteries.