Great effort has recently been made to develop unique nanomaterials with superior reflection loss (RL), thin thickness, wide bandwidth and low density to improve their efficiency in electromagnetic ...(EM) microwave absorption, while maintaining a simple manufacturing process. The use of traditional nanomaterials with magnetic loss or dielectric loss, of course, not only makes the last requirement hard to meet but also restricts the thickness of absorber, and limits mass production. Recently, some promising nanomaterials with excellent conduction loss and polarization loss have been explored which promise to enable unique nanostructures with multiple reflections and interfacial polarization. Herein, we discuss the EM microwave absorption theory. Then, we review recent achievements in manufacturing EM microwave absorption materials, particularly focusing on the unique and key factors in design and control of structures and components. In addition, current challenges are presented, and prospects for future development in this rapidly blossoming field are discussed.
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•Discuss the microwave absorption theory.•Highlight recent achievements in various types of EM microwave absorption materials.•Comment on remaining challenges and provide prospects for further developments in this blossoming field.
Hydrogen storage materials are the key to hydrogen energy utilization. However, current materials can hardly meet the storage capacity and/or operability requirements of practical applications. Here ...we report an advancement in hydrogen storage performance and related mechanism based on a hydrofluoric acid incompletely etched MXene, namely, a multilayered Ti2CTx (T is a functional group) stack that shows an unprecedented hydrogen uptake of 8.8 wt% at room temperature and 60 bar H2. Even under completely ambient conditions (25 °C, 1 bar air), Ti2CTx is still able to retain ~4 wt% hydrogen. The hydrogen storage is stable and reversible in the material, and the hydrogen release is controllable by pressure and temperature below 95 °C. The storage mechanism is deduced to be a nanopump-effect-assisted weak chemisorption in the sub-nanoscale interlayer space of the material. Such a storage approach provides a promising strategy for designing practical hydrogen storage materials.An incompletely etched Ti2CTx stack exhibits highly reversible hydrogen storage under near-ambient conditions by nanopump-effect-assisted weak chemisorption.
Porous carbon nanotubes/cobalt nanoparticles (CNTs/Co) composite with dodecahedron morphology was synthesized by in situ pyrolysis of the Co-based zeolitic imidazolate framework in a reducing ...atmosphere. The morphology and microstructure of the composite can be well tuned by controlling the pyrolysis conditions. At lower pyrolysis temperature, the CNTs/Co composite is composed of well-dispersed Co nanoparticles and short CNT clusters with low graphitic degree. The increase of pyrolysis temperature/time promotes the growth and graphitization of CNTs and leads to the aggregation of Co nanoparticles. The optimized CNTs/Co composite exhibits strong dielectric and magnetic losses as well as a good impedance matching property. Interestingly, the CNTs/Co composite displays extremely strong electromagnetic wave absorption with a maximum reflection loss of −60.4 dB. More importantly, the matching thickness of the absorber is as thin as 1.81 mm, and the filler loading of composite in the matrix is only 20 wt %. The highly efficient absorption is closely related to the well-designed structure and the synergistic effect between CNTs and Co nanoparticles. The excellent absorbing performance together with lightweight and ultrathin thickness endows the CNTs/Co composite with the potential for application in the electromagnetic wave absorbing field.
Simultaneously increasing the activity and stability of the single-atom active sites of M-N-C catalysts is critical but remains a great challenge. Here, we report an Fe-N-C catalyst with ...nitrogen-coordinated iron clusters and closely surrounding Fe-N
active sites for oxygen reduction reaction in acidic fuel cells. A strong electronic interaction is built between iron clusters and satellite Fe-N
due to unblocked electron transfer pathways and very short interacting distances. The iron clusters optimize the adsorption strength of oxygen reduction intermediates on Fe-N
and also shorten the bond amplitude of Fe-N
with incoherent vibrations. As a result, both the activity and stability of Fe-N
sites are increased by about 60% in terms of turnover frequency and demetalation resistance. This work shows the great potential of strong electronic interactions between multiphase metal species for improvements of single-atom catalysts.
Commonly, one typical performance of the materials can be fully utilized in a certain field due to the particular physical or chemical properties. In this work, a multifunctional novel necklace-like ...three-dimension (3D) Fe3O4/CNTs nanocomposite with carbon nanotubes (CNTs) threading into homogeneous spherical Fe3O4 nanoparticles have been fabricated by a one-pot hydrothermal method. The good intrinsic magnetic and dielectric properties for the 3D Fe3O4/CNTs nanocomposites lead to their outstanding microwave absorption performances (minimum RL value of −59.2 dB with a thin thickness of 1.68 mm). Furthermore, high electrical conductivity and fast surface redox are also observed in these Fe3O4/CNTs nanocomposites resulting in their excellent electrochemical properties (specific capacitance of 361.1 F g−1 at 0.5 A g−1). This work indicates that the distinct physical and chemical properties can be realized in the same composite structure by the suitable composite technology, which can not only improve the material utilization but also enable the preparation of multifunctional devices.
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•A multifunctional necklace-like 3D Fe3O4/CNTs nanocomposites are fabricated.•The good magnetic and dielectric properties lead to outstanding microwave absorption.•The high conductivity and fast surface redox resulting in excellent electrochemical properties.•Fe3O4/CNTs exhibit extraordinary microwave absorption and supercapacitor performances.
Carbon-based magnetic composites are promising alternatives to pure magnetic nanoparticles (MOx, M = Fe, Co, Ni) and spinel ferrites (MFe2O4, M = Fe, Co, Ni, Mn, Zn) as electromagnetic (EM) wave ...absorption materials, which however suffer from complex processes and have poor microwave absorption properties. Herein, we anchored Fe3O4 porous spheres onto carbon nanotubes (CNTs) via a simple solvothermal method. The formed Fe3O4/CNTs nanocomposites show a three-dimension (3D) network. The improved effective bandwidth (3.9 GHz) and, more importantly, remarkable EM microwave absorption performances (−51 dB at 5.52 GHz) are observed in 3D Fe3O4/5 wt% CNTs nanocomposites. The enhanced microwave absorption performances are attributed to the high surface areas and porous structure of magnetic Fe3O4 spheres, which presented a good synergetic role with CNTs. Furthermore, the controllable permittivity in nanocomposites was developed by adjusting the CNT content, which balanced the permeability to obtain a good impedance matching. This work demonstrates a simple approach to enhancing the microwave absorption performances of EM wave absorption materials.
Natural alginate fibers are used as templates to fabricate CoFe alloy-decorated hierarchically porous carbon fibers (HPCFs). Due to the coordination with negatively charged α−L−guluronate blocks, ...transition metal (TM) ions could be confined in the “egg box” structure of alginate, which convert to CoFe alloy particles that homogenously embedded in HPCFs during carbonization. The composition and weight ratio of magnetic particles could be well controlled by adjusting the absorbed TM ions and carbonization temperature. Unlike previous analogues with uniform mesopores, this composite fiber simultaneously possesses a number of mesopores and a high proportion of submicron macropores which not only facilitates the accommodation of large-sized CoFe particles, but also induces abundant interfacial polarization and EMW multi-scattering. Remarkably, the CoFe/HPCF with a filler loading as low as 15 wt% in matrix achieves an extremely strong reflection loss of −69.1 dB at a thin thickness of 1.6 mm, and its effective absorption bandwidth reaches 5.2 GHz, showing better comprehensive properties than other similar absorbers. This work highlights the importance of hierarchically porous structure (especially macroporous structure) on improving EMW absorption. The synthetic strategy is green, low cost, scalable, and can be used to synthesize other highly efficient composite absorbers.
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Design and synthesis of highly efficient and cost-effective bifunctional catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) remain a big challenge. Herein, a ...quaternary amorphous nanocompound Ni-Fe-P-B has been synthesized by a facile, scalable co-reduction method. The Ni-Fe-P-B exhibits high electrocatalytic activity and outstanding durability for both HER and OER, delivering a current density of 10 mAcm
−2
at overpotentials of 220 and 269 mV, respectively. When loaded on carbon fiber paper (CFP) as a bifunctional catalyst, the Ni-Fe-P-B@CFP electrode requires a low cell voltage of 1.58 V to obtain 10 mAcm
−2
for overall water splitting with negligible recession over 60 h. The excellent catalytic performances of Ni-Fe-P-B mainly benefit from the metal-metalloid combined composition modulation and the unique amorphous structure. This work provides new insights into the design of robust bifunctional catalysts for water splitting, and may promote the development of multicomponent amorphous catalysts.
Abstract
Ce
3+
-doped yttrium aluminum garnet (YAG:Ce) nanocrystals were successfully synthesized via a facile sol-gel method. Multiple characterization techniques were employed to study the ...structure, morphology, composition and photoluminescence properties of YAG:Ce nanophosphors. The YAG:Ce
0.0055
sintered at 1030 °C exhibited a typical 5
d
1
-4
f
1
emission band with the maximum peak located at 525 nm, and owned a short fluorescence lifetime
τ
1
(~28 ns) and a long fluorescence lifetime
τ
2
(~94 ns). Calcination temperature and Ce
3+
doping concentration have significant effects on the photoluminescence properties of the YAG:Ce nanophosphors. The emission intensity was enhanced as the calcination temperature increased from 830 to 1030 °C, but decreased dramatically with the increase of Ce
3+
doping concentration from 0.55 to 5.50 at.% due to the concentration quenching. By optimizing the synthesized condition, the strongest photoluminescence emission intensity was achieved at 1030 °C with Ce
3+
concentration of 0.55 at.%.
Highlights
Stretchable MXene organohydrogel contains MXene network for electron conduction and water/glycerin binary solvent for ion transmission was prepared.
The MXene organohydrogel exhibits ...exceptionally enhanced EMI shielding performance compared to hydrogel, as well as low-temperature tolerance, anti-drying ability.
Conductive hydrogels have potential applications in shielding electromagnetic (EM) radiation interference in deformable and wearable electronic devices, but usually suffer from poor environmental stability and stretching-induced shielding performance degradation. Although organohydrogels can improve the environmental stability of materials, their development is at the expense of reducing electrical conductivity and thus weakening EM interference shielding ability. Here, a MXene organohydrogel is prepared which is composed of MXene network for electron conduction, binary solvent channels for ion conduction, and abundant solvent-polymer-MXene interfaces for EM wave scattering. This organohydrogel possesses excellent anti-drying ability, low-temperature tolerance, stretchability, shape adaptability, adhesion and rapid self-healing ability. Two effective strategies have been proposed to solve the problems of current organohydrogel shielding materials. By reasonably controlling the MXene content and the glycerol-water ratio in the gel, MXene organohydrogel can exhibit exceptionally enhanced EM interference shielding performances compared to MXene hydrogel due to the increased physical cross-linking density of the gel. Moreover, MXene organohydrogel shows attractive stretching-enhanced interference effectiveness, caused by the connection and parallel arrangement of MXene nanosheets. This well-designed MXene organohydrogel has potential applications in shielding EM interference in deformable and wearable electronic devices.
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