Enhanced Electromagnetic Wave Absorption Properties of Poly(3,4-ethylenedioxythiophene) Nanofi ber-Decorated Graphene Sheets by Non-covalent Interactions

Graphene sheets(GNs) have high conductivity, but they exhibit weak electromagnetic(EM) wave absorption performance. Here, poly(3,4-ethylenedioxythiophene)(PEDOT) nanofibers were decorated on the surface of GNs in which the residual defects and groups act as the active sites and therefore are beneficial for the deposition of PEDOT nanofibers.The SEM images display that PEDOT nanofibers are successfully decorated on the surface of GNs through in situ polymerization. The diameter of the PEDOT nanofibers were ranged from 15 to 50 nm with hundreds of nanometers in length. The EM wave absorption properties of graphene, PEDOT, and GNs-PEDOT were also investigated. Compared to pure graphene and PEDOT, the EM wave absorption properties of GNs-PEDOT improved significantly. The maximum value of RLwas up to-48.1 d B at 10.5 GHz with a thickness of only 2 mm. Meanwhile, the absorption bandwidth of RL values below-10 d B was 9.4 GHz(5.8–12.3, 12.9–15.8 GHz) in the thickness of 1.5–3 mm. The enhancement is attributed to the modification of PEDOT and the unique structure of nanofibers. On one hand, the deposition of PEDOT nanofibers on the surface of GNs decreases the conductivity of graphene, and makes impedance match better. On the other hand, the unique structure of PEDOT nanofibers results in relatively large specific surfaces areas, providing more active sites for reflection and scattering of EM waves. Therefore, our findings demonstrate that the deposition of conducting polymers on GNs by non-covalent bond is an efficient way to fabricate strong EM wave absorbers.

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 d B 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.

Multi-heteroatom doped porous carbon derived from insect feces for capacitance-enhanced sodium-ion storage

The large-scale application of sodium ion batteries(SIBs)is limited by economic and environmental factors.Here,we prepare multi-heteroatom self-doped hierarchical porous carbon(HHPC)with a honeycomb-like structure by one-step carbonization method using high-yield and low-cost biomass silkworm excrement as a precursor.As an anode for SIB,HHPC-1100 exhibits a capacity of 331.7 mA h g^(-1) at 20 mA g^(-1),while it also reveals remarkable rate performance and stable long cycle capability due to its abundant pore structure and proper amount of hetero atom doping.Moreover,the synergistic effect of O,N,S,P co-doping in carbon materials on sodium ion adsorption is verified by the first-principles study,which provide a theoretical basis for the prominent electrochemical performance of the material.

MoS_(2)-Decorated/Integrated Carbon Fiber:Phase Engineering Well-Regulated Microwave Absorber

Phase engineering is an important strategy to modulate the electronic structure of molybdenum disulfide(MoS_(2)).MoS_(2)-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 MoS_(2) is achieved via a facile one-step hydrother-mal route,in which the 1T phase is induced by the intercalation of guest molecules and ions.The EMW absorption mechanism of single MoS_(2) is revealed by presenting a comparative study between 1T/2H MoS_(2) and 2H MoS_(2).As a result,1T/2H MoS_(2) with the matrix loading of 15%exhibits excellent microwave absorption property than 2H MoS_(2).Furthermore,taking the advantage of 1T/2H MoS_(2),a flexible EMW absorbers that ultrathin 1T/2H MoS_(2)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.

MOF-derived multifunctional filler reinforced polymer electrolyte for solid-state lithium batteries

Solid-state lithium batteries(SSLBs) have attracted great interest from researchers due to their inherent high energy density and high safety performance.In order to develop SSLBs,the following two key problems should be solved:(1) Improving the lithium ion conductivity of solid electrolyte at room temperature;and(2) improving the interface between the electrode and the electrolyte.Herein,we propose a new multifunctional filler for reinforcing polymer electrolytes.The composite solid electrolytes(CSEs)mainly contain a MOF-derived Co-doped hollow porous carbon nanocage,which absorbs Li~+ containing ionic liquid(Li-ILs@HPCN),polyethylene oxide(PEO) and lithium bis(trifluoromethanesulfonyl)imide.By optimizing the composition of the CSEs,the CSEs membrane with high ionic conductivity(1.91×10^(-4) S cm^(-1) at 30℃),wide electrochemical stability(5.2 V) and high mobility of lithium ion(0.5) was obtained.Even at a current density of 0.2 mA cm^(-2),the PILH electrolyte possesses excellent interfacial stability against Li metal in Li symmetrical batteries exceeds 1600 h.Finally,the SSLBs(LFP/PILH/Li) showed excellent cycle stability,and the capacity was maintained at 152.9 and140.0 mA h g^(-1) after 150 cycles at a current density of 0.2 C and 0.5 C.This work proposes a completely new strategy for building high-performance SSLBs.

Metal–phenolic coordination crystals derived magnetic hollow carbon spheres for ultrahigh electromagnetic wave absorption

Owing to the tunable compositions and versatile functionality,the development of eco-friendly metal–phenolic coordination crystals derivatives is highly anticipated for electromagnetic wave absorption.In this study,three kinds of magnetic hollow carbon spheres(HCSs)with macro-meso-microporous characteristics,including Fe/HCS,Co/HCS,and CoNi/HCS,are successfully fabricated via the co-operative hard template and self-assembling process,in which magnetic particles are encapsulated in carbon shell matrix after the pyrolysis of metal–polyphenol coordination crystals and further subsequent template removal.On the one hand,hierarchical macro-meso-micropores effectively balance the impedance gap between absorbers and air and introduce structural defects or distortion,leading to matched impedance and enhanced dipolar/defect polarization.On the other hand,wrapped magnetic particles provide uncountable hetero-interfaces and induce ferromagnetic resonance,resulting in strengthened interfacial polarization and additional magnetic loss.In particular,enhanced minimum reflection loss(RL,min)and broadband effective absorption bandwidth(EAB)are achieved with only 10 wt.%filler loading.Specifically,the RL,min and EAB values are-57.5 dB and 7.2 GHz for Fe/HCS,-50.0 dB and 5.8 GHz for Co/HCS,and-52.1 dB and 6.7 GHz for CoNi/HCS,respectively.Moreover,this work provides us a modular-assembly strategy to regulate the hollow cavity of absorbers and simultaneously manipulates the chemical components of absorbers to regulate electromagnetic wave absorption performance.

Hierarchical design of FeCo-based microchains for enhanced microwave absorption in C band

Microwave absorbing materials(MAMs)has been intensively investigated in order to meet the requirement of electromagnetic radiation control,especially in S and C band.In this work,FeCo-based magnetic MAMs are hydrothermally synthesized via a magnetic-field-induced process.The composition and morphology of the MAMs are capable of being adjusted simultaneously by the atomic ratio of Fe2+to Co2+in the precursor.The hierarchical magnetic microchain,which has a core–shell structure of twodimensional FexCo1−xOOH nanosheets anchored vertically on the surface of a one-dimensional(1D)Co microchain,shows significantly enhanced microwave absorption in C band,resulting in a reflection loss(RL)of lower than−20 dB at frequencies ranging from 4.4 to 8.0 GHz under a suitable matching thickness.The magnetic coupling of Co microcrystals and the double-loss mechanisms out of the core-shell structure are considered to promote the microwave attenuation capability.The hierarchical design of 1D magnetic MAMs provides a feasible strategy to solve the electromagnetic pollution in C band.

Hierarchical construction of CNT networks in aramid papers for high-efficiency microwave absorption

Carbon nanotubes(CNTs)incorporated polymeric composites have been extensively investigated for microwave absorption at target frequencies to meet the requirement of radar cross-section reduction.In this work,a strategy of efficient utilization of CNT in producing CNT incorporated aramid papers is demonstrated.The layer-by-layer self-assembly technique is used to coat the surfaces of meta-aramid fibers and fibrils with CNT,providing novel raw materials available for the large-scale papermaking.The hierarchical construction of CNT networks resolves the dilemma of increasing CNT content and avoiding the agglomeration of CNT,which is a frequent challenge for CNT incorporated polymeric composites.The composite paper,which contains abundant heterogeneous interfaces and long-range conductive networks,is capable of reaching a high permittivity and dielectric loss tangent at a low CNT loading,its complex permittivity is,so far,adjustable in the range of(1.20−j0.05)to(25.17−j18.89)at 10 GHz.Some papers with optimal matching thicknesses achieve a high-efficiency microwave absorption with a reflection loss lower than−10 dB in the entire X-band.

Synthesis of covalently bonded reduced graphene oxide-Fe_(3)O_(4) nanocomposites for efficient electromagnetic wave absorption

High-performance electromagnetic(EM)wave absorbers,covalently bonded reduced graphene oxideFe_(3)O_(4) nanocomposites(rGO-Fe_(3)O_(4)),are synthesized via hydrothermal reaction,amidation reaction and reduction process.The microstructure,surface element composition and morphology of rGO-Fe_(3)O_(4) nanocomposites are characterized and corresponding EM wave absorption properties are analyzed in great detail.It demonstrates that Fe_(3)O_(4) nanoparticles are successfully covalently grafted onto graphene by amide bonds.When the mass ratio of rGO and Fe_(3)O_(4) is 2:1(sample S2),the absorber exhibits the excellent EM wave absorption performance that the maximum reflection loss(RL)reaches up to-48.6 dB at 14.4 GHz,while the effective absorption bandwidth(RL<-10 dB)is 6.32 GHz(11.68-18.0 GHz)with a matching thickness of 2.1 mm.Furthermore,radar cross section(RCS)simulation calculation is also adopted to evaluate the ability of absorbers to scatter EM waves,which proves again that the absorption performance of absorber S2 is optimal.The outstanding EM wave absorption performance is attributed to the synergistic effect between dielectric and magnetic loss,good attenuation ability and excellent impedance matching.Moreover,covalent bonds considered to be carrier channels can facilitate electron migration,adjust EM parameters and then enhance EM wave absorption perfo rmance.This work provides a possible method for preparing efficient EM wave absorbers.

MOFs derived magnetic porous carbon microspheres constructed by core-shell Ni@C with high-performance microwave absorption

Lightweight and high-performance are two determining factors for metal-organic-frameworks(MOFs)derived microwave absorbers.However,most of the reported MOFs derived absorbers usually possess high filler loading.Herein,a series of MOFs derived magnetic porous carbon microspheres with tunable diameter and high specific surface area have been synthesized via a pyrolysis process.The synthesized magnetic porous carbon microspheres,constructed by uniformly distributed core-shell Ni@C,exhibit high-performance microwave absorption with a low filler loading of 10 wt%.Considering the mciro-mesoporous structures,matched impedance,strong conductive loss,enhanced dipolar/interfacial polarization as well as strong magnetic coupling network,a minimum reflection loss of-60 dB and an absorption bandwidth of 7.0 GHz can be achieved at 2.6 mm.Moreover,the bandwidth reaches as wide as 10.2 GHz when the thickness is 4 mm.In addition,compared with other MOFs derived absorbers,this work provides us a simple strategy for the synthesis of porous carbon microspheres with lightweight and high-performance microwave absorption for practical applications.

Experimental design and theoretical evaluation of nitrogen and phosphorus dual-doped hierarchical porous carbon for high-performance sodium-ion storage

Starch has a wide range of sources and can be used as a high-quality precursor for sodium-ion battery anode materials.However,the carbonization yield and specific capacity of carbon materials obtained by directly pyrolyzing starch are low.Herein,starch is used as the carbon source,and ammonium polyphosphate(APP)is used as the cross-linking agent and dopant to prepare a nitrogen and phosphorus co-doped porous carbon(NPPC).As the anode for sodium-ion batteries,NPPC-2 exhibits a high reversible capacity of 385.8 mAhg^(-1)at 50 mAg^(-1).Even after 1000 cycles at a large current density of 5 Ag^(-1),the reversible capacity can still be maintained at 126.9 mAhg^(-1).Based on detailed data and first-principles calculations,the excellent performance of NPPC is due to the effective doping of nitrogen and phosphorus elements,which distorts the graphite sheet,introduces defects,and increases the graphite layer spacing,thereby enhancing the adsorption capacity of the carbon material for sodium ions,reducing the diffusion barrier of sodium ions.This work provides a new idea for heteroatom doping and carbon material modification.

Heteroatoms-doped carbon nanocages with enhanced dipolar and defective polarization toward light-weight microwave absorbers

Light-weight and exceptional microwave absorption are two vital characteristics for microwave absorbers in practical applications,but still face challenges.Herein,we employ a sacrificial template strategy to fabricate heteroatoms-doped carbon nanocages(CNs)via chemical vapor deposition,in which heteroatoms are simultaneously doped into the carbon frameworks by bubbling flowing source liquid.Compared with CNs,doped heteroatoms,accompanied with the inevitably defective arrangements in the lattice,not only decrease the electrical conductivity and balance the impedance characteristics,but also introduce structuralchemical defects and trigger dominant dipolar/defect polarization.As a result,both the minimum reflection loss(R_(L,min))and effective absorption bandwidth(EAB)greatly increase at an ultralow filler loading of 5 wt.%owing to internal hollow void and high specific surface area.The R_(L,min) values reach−53.6,−43.2,and−50.1 dB for N-CNs,S-CNs,and N,S-CNs with the corresponding EAB of 4.9,2.5,and 3.1 GHz,respectively.Furthermore,this work provides an effective strategy for the construction of heteroatoms-doped hollow carbon frameworks in large-scale production and the obtained doped carbon nanocages can be used as light-weight and high-performance microwave absorbers.

Heterogeneous junctions of magnetic Ni core@binary dielectric shells toward high-efficiency microwave attenuation

Metal-organic-frameworks(MOFs)derived carbon-based composites with balanced impedance matching and synergistic dielectric/magnetic loss are considered as promising microwave absorbers.With the aim to promote interfacial polarization,herein,heterogeneous junctions composed of magnetic Ni core and binary dielectric shells(C and PEDOT)are synthesized by annealing Ni-MOFs precursors and an in-situ polymerization strategy,forming Ni@C@PEDOT spheres with multilayer heterogeneous interfaces.The results indicate that the final absorption attenuation is sensitive to the thickness of the dielectric PEDOT layer,when the thickness of the PEDOT layer is 224 nm,an optimal reflection loss of-72.4 d B is achieved at 2 mm and the effective absorption bandwidth reaches 6.4 GHz with a thickness of only 1.85 mm,the excellent absorption attenuation is accredited to the promoted impedance matching,enhanced conduction loss as well as the synergistic interfacial polarization induced by magnetic core and binary dielectric shells.Meanwhile,this work offers a simple and significant strategy in preparation for ideal microwave absorbers by rational design of multilayer heterogeneous interfaces.

Multi-dimensional Ni@C-CoNi composites with strong magnetic interaction toward superior microwave absorption

Dielectric-magnetic integrated absorbers have attracted arousing attention in microwave absorption,however,it still remains a great challenge to simultaneously achieve superior dielectric polarization and strong magnetic loss.Herein,we propose a multi-scale structure optimization strategy to anchor CoNiMOFs derived OD CoNi alloy onto 1 D core-shell Ni@C surface.By decorating with the poly-dopamine layer,the connection between 1 D NiO and CoNi-MOFs precursors was greatly improved via the electrostatic interaction.Benefiting from the overlapping conductive networks,enhanced interfacial polarization among the multi-dimensional heterogeneous interfaces and strong magnetic interaction,the fabricated multi-dimensional Ni@C-CoNi composites exhibit outstanding microwave absorption.Typically,the optimal reflection loss is as high as-51.4 dB at 1.9 mm,and the effective absorption bandwidth achieves 4.6 GHz with a thickness of only 1.3 mm.This multi-scale structure optimization strategy inspires us with an efficient method to fabricate ideal microwave absorbers and the obtained multi-dimensional composites can be used as promising candidates in electromagnetic radiation protection.