Broadband and Tunable High‐Performance Microwave Absorption of an Ultralight and Highly Compressible Graphene Foam
TL;DR: The broadband and tunable high-performance microwave absorption properties of an ultralight and highly compressible graphene foam (GF) are investigated and it is shown that via physical compression, the microwave absorption performance can be tuned.
Abstract: The broadband and tunable high-performance microwave absorption properties of an ultralight and highly compressible graphene foam (GF) are investigated. Simply via physical compression, the microwave absorption performance can be tuned. The qualified bandwidth coverage of 93.8% (60.5 GHz/64.5 GHz) is achieved for the GF under 90% compressive strain (1.0 mm thickness). This mainly because of the 3D conductive network.
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TL;DR: The mechanical flexibility and easy coating capability offered by MXenes and their composites enable them to shield surfaces of any shape while providing high EMI shielding efficiency.
Abstract: Materials with good flexibility and high conductivity that can provide electromagnetic interference (EMI) shielding with minimal thickness are highly desirable, especially if they can be easily processed into films. Two-dimensional metal carbides and nitrides, known as MXenes, combine metallic conductivity and hydrophilic surfaces. Here, we demonstrate the potential of several MXenes and their polymer composites for EMI shielding. A 45-micrometer-thick Ti3C2Tx film exhibited EMI shielding effectiveness of 92 decibels (>50 decibels for a 2.5-micrometer film), which is the highest among synthetic materials of comparable thickness produced to date. This performance originates from the excellent electrical conductivity of Ti3C2Tx films (4600 Siemens per centimeter) and multiple internal reflections from Ti3C2Tx flakes in free-standing films. The mechanical flexibility and easy coating capability offered by MXenes and their composites enable them to shield surfaces of any shape while providing high EMI shielding efficiency.
3,251 citations
TL;DR: For the first time, an efficient and facile approach is reported to fabricate freestanding, flexible, and hydrophobic MXene foam with reasonable strength by assembling MXene sheets into films followed by a hydrazine-induced foaming process.
Abstract: Ultrathin, lightweight, and flexible electromagnetic-interference (EMI) shielding materials are urgently required to manage increasingly serious radiation pollution. 2D transition-metal carbides (MXenes) are considered promising alternatives to graphene for providing excellent EMI-shielding performance due to their outstanding metallic electrical conductivity. However, the hydrophilicity of MXene films may affect their stability and reliability when applied in moist or wet environments. Herein, for the first time, an efficient and facile approach is reported to fabricate freestanding, flexible, and hydrophobic MXene foam with reasonable strength by assembling MXene sheets into films followed by a hydrazine-induced foaming process. In striking contrast to well-known hydrophilic MXene materials, the MXene foams surprisingly exhibit hydrophobic surfaces and outstanding water resistance and durability. More interestingly, a much enhanced EMI-shielding effectiveness of ≈70 dB is achieved for the lightweight MXene foam as compared to its unfoamed film counterpart (53 dB) due to the highly efficient wave attenuation in the favorable porous structure. Therefore, the hydrophobic, flexible, and lightweight MXene foam with an excellent EMI-shielding performance is highly promising for applications in aerospace and portable and wearable smart electronics.
1,241 citations
TL;DR: Graphene networks with "well-sequencing genes" can serve as nanogenerators, thermally promoting electromagnetic wave absorption by 250%, with broadened bandwidth covering the whole investigated frequency, opening up an unexpected horizon for converting, storing, and reusing waste electromagnetic energy.
Abstract: Electromagnetic energy radiation is becoming a "health-killer" of living bodies, especially around industrial transformer substation and electricity pylon. Harvesting, converting, and storing waste energy for recycling are considered the ideal ways to control electromagnetic radiation. However, heat-generation and temperature-rising with performance degradation remain big problems. Herein, graphene-silica xerogel is dissected hierarchically from functions to "genes," thermally driven relaxation and charge transport, experimentally and theoretically, demonstrating a competitive synergy on energy conversion. A generic approach of "material genes sequencing" is proposed, tactfully transforming the negative effects of heat energy to superiority for switching self-powered and self-circulated electromagnetic devices, beneficial for waste energy harvesting, conversion, and storage. Graphene networks with "well-sequencing genes" (w = Pc /Pp > 0.2) can serve as nanogenerators, thermally promoting electromagnetic wave absorption by 250%, with broadened bandwidth covering the whole investigated frequency. This finding of nonionic energy conversion opens up an unexpected horizon for converting, storing, and reusing waste electromagnetic energy, providing the most promising way for governing electromagnetic pollution with self-powered and self-circulated electromagnetic devices.
719 citations
TL;DR: Considering the promising performance of Ti3C2 MXenes with the modified surface, this work is expected to open the door for the expanded applications of MXenes family in EM absorbing and shielding fields.
Abstract: Electromagnetic (EM) absorbing and shielding composites with tunable absorbing behaviors based on Ti3C2 MXenes are fabricated via HF etching and annealing treatment. Localized sandwich structure without sacrificing the original layered morphology is realized, which is responsible for the enhancement of EM absorbing capability in the X-band. The composite with 50 wt % annealed MXenes exhibits a minimum reflection loss of −48.4 dB at 11.6 GHz, because of the formation of TiO2 nanocrystals and amorphous carbon. Moreover, superior shielding effectiveness with high absorption effectiveness is achieved. The total and absorbing shielding effectiveness of Ti3C2 MXenes in a wax matrix with a thickness of only 1 mm reach values of 76.1 and 67.3 dB, while those of annealed Ti3C2 MXenes/wax composites are 32 and 24.2 dB, respectively. Considering the promising performance of Ti3C2 MXenes with the modified surface, this work is expected to open the door for the expanded applications of MXenes family in EM absorbing an...
691 citations
TL;DR: The method of utilizing an external voltage to break the intrinsic dielectric feature by modifying a traditional electronic absorption device is demonstrated for the first time and has great significance in solving the low-frequency electromagnetic interference issue.
Abstract: Nowadays, low-frequency electromagnetic interference (<2.0 GHz) remains a key core issue that plagues the effective attenuation performance of conventional absorption devices prepared via the component-morphology method (Strategy I). According to theoretical calculations, one fundamental solution is to develop a material that possesses a high e' but lower e″. Thus, it is attempted to control the dielectric values via applying an external electrical field, which inducts changes in the macrostructure toward a performance improvement (Strategy II). A sandwich-structured flexible electronic absorption device is designed using a carbon film electrode to conduct an external current. Simultaneously, an absorption layer that is highly responsive to an external voltage is selected via Strategy I. Relying on the synergistic effects from Strategies I and II, this device demonstrates an absorption value of more than 85% at 1.5-2.0 GHz with an applied voltage of 16 V while reducing the thickness to ≈5 mm. In addition, the device also shows a good absorption property at 25-150 °C. The method of utilizing an external voltage to break the intrinsic dielectric feature by modifying a traditional electronic absorption device is demonstrated for the first time and has great significance in solving the low-frequency electromagnetic interference issue.
657 citations
References
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TL;DR: The direct synthesis of three-dimensional foam-like graphene macrostructures, which are called graphene foams (GFs), by template-directed chemical vapour deposition is reported, demonstrating the great potential of GF/poly(dimethyl siloxane) composites for flexible, foldable and stretchable conductors.
Abstract: [Chen, Zongping; Ren, Wencai; Gao, Libo; Liu, Bilu; Pei, Songfeng; Cheng, Hui-Ming] Chinese Acad Sci, Shenyang Natl Lab Mat Sci, Inst Met Res, Shenyang 110016, Peoples R China.;Cheng, HM (reprint author), Chinese Acad Sci, Shenyang Natl Lab Mat Sci, Inst Met Res, Shenyang 110016, Peoples R China;cheng@imr.ac.cn
3,517 citations
TL;DR: In this paper, the absorption properties of CNT/crystalline Fe nanocomposites have been investigated and it was shown that the absorption property is due to the confinement of crystalline Fe in carbon nanoshells, deriving mainly from magnetic rather than electric effects.
Abstract: CNT/crystalline Fe nanocomposites (see Figure) have excellent microwave-absorption characteristics. This absorption property is shown to result from the confinement of crystalline Fe in carbon nanoshells, deriving mainly from magnetic rather than electric effects-the complex permittivity and permeability depend both on the shape and phase of the CNT/Fe nanocapsulates.
1,780 citations
TL;DR: All carbon aerogels with ultralow density and temperature-invariant super-elasticity are fabricated by facile assembling of commercial carbon nanotubes and chemically-converted giant graphene sheets, on the basis of the synergistic effect between elastic CNTs ribs and giant graphene cell walls.
Abstract: All carbon aerogels (up to 1000 cm(3)) with ultralow density (down to 0.16 mg cm(-3)) and temperature-invariant (-190-900 °C) super-elasticity are fabricated by facile assembling of commercial carbon nanotubes (CNTs) and chemically-converted giant graphene sheets, on the basis of the synergistic effect between elastic CNTs ribs and giant graphene cell walls.
1,680 citations
TL;DR: It is believed that high electrical conductivity and connectivity of the conductive fi llers can improve EMI shielding performance.
Abstract: IO N The rapid development of modern electronics packed with highly integrated circuits generates severe electromagnetic radiation, which leads to harmful effects on highly sensitive precision electronic equipment as well as the living environment for human beings. Great effort has been made for the development of high-performance electromagnetic interference (EMI) shielding materials. In addition to high EMI shielding performance, being lightweight and fl exible are two other important technical requirements for effective and practical EMI shielding applications especially in areas of aircraft, aerospace, automobiles, and fast-growing next-generation fl exible electronics such as portable electronics and wearable devices. [ 1 ] Recently, electrically conductive polymer composites have received much attention for EMI shielding applications, [ 1–12 ] because of their light weight, resistance to corrosion, fl exibility, good processability, and low cost compared to the conventional metal-based materials. The EMI shielding effectiveness of the polymer composites depends critically on the intrinsic electrical conductivity, dielectric constant, magnetic permeability, aspect ratio, and content of conductive fi llers. [ 1–12 ] It is believed that high electrical conductivity and connectivity of the conductive fi llers can improve EMI shielding performance. [ 1 , 2 , 4 , 7 , 8 ]
1,621 citations
TL;DR: Chemical graphitized r-GOs, as the thinnest and lightest material in the carbon family, exhibit high-efficiency electromagnetic interference shielding at elevated temperature, attributed to the cooperation of dipole polarization and hopping conductivity.
Abstract: Chemical graphitized r-GOs, as the thinnest and lightest material in the carbon family, exhibit high-efficiency electromagnetic interference (EMI) shielding at elevated temperature, attributed to the cooperation of dipole polarization and hopping conductivity. The r-GO composites show different temperature-dependent imaginary permittivities and EMI shielding performances with changing mass ratio.
1,358 citations