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The constantly evolving environment imposes increasingly stringent demands on the mechanical qualities of materials employed for absorbing electromagnetic waves (EMWs). Therefore, there is an urgent need for advanced materials capable of efficiently absorbing EMWs and withstanding harsh electromagnetic conditions. In this study, the electrodeposition method was effectively used to synthesize nickel-cobalt layered double hydroxides (NiCo-LDHs) in a controlled manner on a composite structure of carbon nanotubes and carbon foam, creating an exquisite construction. The manipulation of the electrodeposition time facilitated the regulation of the density of the layered structure within the composite material, thereby significantly enhancing its polarization relaxation performance. Increased defect sites and interface polarization enhance impedance matching and the attenuation constant, resulting in greatly improved absorption performance. The optimized sample demonstrated exceptional wave-absorbing performance in comparative experimental analysis, attaining a maximum reflection loss of -58.18 dB. It also has an effective absorption bandwidth of 5.36 GHz at a wavelength of 2.28 mm. The exceptional isolation effect of LDH, coupled with the outstanding insulation ability of the porous carbon skeleton, confers remarkable corrosion resistance and thermal insulation performance on the composite material. Hence, this discovery offers novel insights into designing environmentally tolerant absorbent materials.

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The exploitation of multicomponent composites (MCCs) has become the main pathway for obtaining advanced microwave absorption materials (MAMs). Herein, a metal valence state modulation strategy is proposed to tune the electromagnetic (EM) parameters and improve microwave absorption performances. Core@shell hollow carbon microspheres@MoSe2 and hollow carbon microspheres@MoSe2/MoOx MCCs with various mixed-valence states content are well-designed and produced by a simple hydrothermal reaction or/and heat treatment process. The results reveal that the thermal treatment of hollow carbon microspheres@MoSe2 in Ar and Ar/H2 leads to the in situ formation of MoOx and multivalence state, respectively, and the enhanced content of Mo4+ in the designed MCCs greatly boosts their impedance matching characteristics, polarization, and conduction loss capacities, which lead to their evidently improved EM wave absorption properties. Amongst, the as-prepared hollow carbon microspheres@MoSe2/MoOx MCCs achieve an effective absorption bandwidth of 5.80 GHz under a matching thickness of 1.97 mm and minimum reflection loss of -21.49 dB. Therefore, this work offers a simple and universal method to fabricate core@shell hollow carbon microspheres@MoSe2/MoOx MCCs, and a novel and feasible metal valence state modulation strategy is proposed to develop high-efficiency MAMs.

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Currently, the microwave absorbers usually suffer dreadful electromagnetic wave absorption (EMWA) performance damping at elevated temperature due to impedance mismatching induced by increased conduction loss. Consequently, the development of high-performance EMWA materials with good impedance matching and strong loss ability in wide temperature spectrum has emerged as a top priority. Herein, due to the high melting point, good electrical conductivity, excellent environmental stability, EM coupling effect, and abundant interfaces of titanium nitride (TiN) nanotubes, they were designed based on the controlling kinetic diffusion procedure and Ostwald ripening process. Benefiting from boosted heterogeneous interfaces between TiN nanotubes and polydimethylsiloxane (PDMS), enhanced polarization loss relaxations were created, which could not only improve the depletion efficiency of EMWA, but also contribute to the optimized impedance matching at elevated temperature. Therefore, the TiN nanotubes/PDMS composite showed excellent EMWA performances at varied temperature (298-573 K), while achieved an effective absorption bandwidth (EAB) value of 3.23 GHz and a minimum reflection loss (RLmin) value of - 44.15 dB at 423 K. This study not only clarifies the relationship between dielectric loss capacity (conduction loss and polarization loss) and temperature, but also breaks new ground for EM absorbers in wide temperature spectrum based on interface engineering.

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Heterointerface engineering is an attractive approach to modulating electromagnetic (EM) parameters and EM wave absorption performance. However, the weak interfacial interactions and poor impedance matching would lead to unsatisfactory EM absorption performance due to the limitation of the construction materials and design strategies. Herein, multilevel heterointerface engineering is proposed by in situ growing nanosheet-like NiCoO2 and selenides with abundant interface structures on 3D-printed graphene aerogel (GA) skeletons, which strengthens the interfacial effect and improves the dielectric polarization loss. Benefiting from the features of substantially enhanced polarization loss and optimized impedance matching, the graphene/S-NiCoO2/selenides (G/S-NCO/Se) have achieved brilliant EM wave absorption performance with a strong reflection loss (RL) value of -60.7 dB and a broad effective absorption bandwidth (EAB) of 8 GHz, which is about six times greater than that of the graphene aerogel (-9.8 dB). Moreover, it is further confirmed by charge density differences and off-axis electron holography that a large amount of polarized charge accumulates at the interface, leading to significant polarization relaxation behaviors. This work provides a deep understanding of the effect of a multilevel heterogeneous interface on dielectric polarization loss, which injects a fresh and infinite vitality for designing high-efficiency EM wave absorbers.

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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.

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The development of extreme performance and multifunctional electromagnetic (EM) wave absorption materials is essential to eliminating undesirable frequency EM pollution. As a promising rare-earth compound, gadolinium oxysulfide (Gd2O2S) has become a significant field of study among nanomaterials with multidisciplinary applications. Herein, the ultrathin Gd2O2S nanosheets with 1 nm thickness were fabricated via a facile hot injection method and then mixed with reduced graphene oxide (rGO) through coassemble and carbonization methods to form Gd2O2S/rGO composites. As a new kind of multifunction EM-wave absorption materials, Gd2O2S/rGO composites exhibited excellent EM-wave absorption performance with an absorption capacity of -65 dB (2.1 mm) and an adequate absorption bandwidth of 5.6 GHz at 1.9 mm. Additionally, their EM-wave absorption mechanisms have been unveiled for the first time. The outstanding EM-wave absorption performance of Gd2O2S/rGO composites could be attributed to the ultrathin Gd2O2S nanosheets with oxygen vacancy and rGO layers with high conductivity and large specific surface area, which will also facilitate the polarization loss, conductivity loss, and multiple reflection and scattering of EM waves between the rGO layer and Gd2O2S nanosheets. Overall, compared to previously reported rGO-based EM-wave absorption materials, this work provides a promising approach for the exploitation and synthesis of Gd2O2S/rGO composites with lightweight and high-performance microwave attenuation.

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Traditional carbon materials such as graphene are often applied in the field of electromagnetic wave (EMW) absorption but they have unbalanced impedance matching and high conductivity. Bio-carbon with graphene-like structure derived from apples has many advantages over graphene: it can be prepared in large quantities and the abundant heteroatoms present in the lattice can provide many polarization phenomena. Herein, Prussian blue analogue (PBA) as a source of magnetic component was combined with bio-carbon or reduced graphene oxide (rGO) to study the EMW absorption properties. The fabricated BC/CFC-12-7 displayed performance with a minimum reflection loss (RLmin) of -72.57 dB and a wide effective absorption bandwidth (EAB) of 5.25 GHz with an ultra-thin and nearly equal matching thickness at 1.61 mm. The results show that the good EMW absorption property of bio-carbon composites comes from good conduction loss, large relaxation polarization loss especially from pyridinic-N, and better impedance matching. The optimized radar cross section is found to be -33.55 dB m2 in the far-field condition using CST. This work explored the advantages of bio-carbon as a novel EMW absorbing material compared with graphene and provided ideas for realizing high-performance EMW absorbing materials in the future.

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Graphene-based aerogels have garnered considerable attention for their lightweight and efficient microwave absorption (MA) properties; however, optimizing the relationship between impedance matching and attenuation capability at low frequencies remains a challenge. In this study, a three-dimensional (3D) silicon carbonitride (SiCN) nanoceramic-coated graphene aerogel with conformal heterogeneous interfaces is constructed by precursor infiltration and pyrolysis to optimize MA performance at low frequencies. Thanks to the enhanced impedance matching and significant interfacial polarization of the two-dimensional sandwiched SiCN/graphene/SiCN cell walls and multiple scattering occurring within the 3D porous skeleton, the aerogel achieves a minimum reflection loss of -57.9 dB at an ultralow frequency of 4.92 GHz (C-band) and a broad bandwidth of 5.0 GHz at an ultralow thickness of 1.7 mm. The strategy developed here provides a method for enhancing dielectric polarization loss in graphene aerogels by the joint optimization of interfacial polarization and impedance matching, inspiring the design of high-performance graphene-based materials for low-frequency MA.

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Introducing a coating shell between the filler and matrix is an effective way to reduce the dielectric loss of the particle/matrix dielectric composites. It found that besides the improvement in interface compatibility, there may be some other effects of the coating shell, such as the elimination of the dielectric mismatch. However, the specific mechanism is still unclear due to the absence of an effective model for the quantitative analysis of the relationship between core-shell structure and dielectric loss, hindering the progress of the dielectric composite design. Here, a phase-field model for simulating high-frequency, alternating-field polarization is employed to study the relationship between high-frequency polarization loss and the coating shell in the silicon dioxide coating boron nitride polytetrafluoroethylene-based (BN@SiO2/PTFE) composite. The results show that the dielectric mismatch makes the high-frequency polarization loss spatially localized and periodically time-variant. The reduction of polarization loss depends on the polarization loss of SiO2. To reduce the high-frequency dielectric loss of the composite, the coating shell should not only eliminate the dielectric mismatch, but its dielectric loss must also be lower than that of the core filler. Furthermore, the model provided in this work has the potential to extend the quantitative calculation of non-intrinsic polarization loss and conduction loss.

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The integration of nano-semiconductors into electromagnetic wave absorption materials is a highly desirable strategy for intensifying dielectric polarization loss; achieving high-attenuation microwave absorption and realizing in-depth comprehension of dielectric loss mechanisms remain challenges. Herein, ultrafine oxygen vacancy-rich Nb2O5 semiconductors are confined in carbon nanosheets (ov-Nb2O5/CNS) to boost dielectric polarization and achieve high attenuation. The polarization relaxation, electromagnetic response, and impedance matching of the ov-Nb2O5/CNS are significantly facilitated by the Nb2O5 semiconductors with rich oxygen vacancies, which consequently realizes an extremely high attenuation performance of - 80.8 dB (> 99.999999% wave absorption) at 2.76 mm. As a dielectric polarization center, abundant Nb2O5-carbon heterointerfaces can intensify interfacial polarization loss to strengthen dielectric polarization, and the presence of oxygen vacancies endows Nb2O5 semiconductors with abundant charge separation sites to reinforce electric dipole polarization. Moreover, the three-dimensional reconstruction of the absorber using microcomputer tomography technology provides insight into the intensification of the unique lamellar morphology regarding multiple reflection and scattering dissipation characteristics. Additionally, ov-Nb2O5/CNS demonstrates excellent application potential by curing into a microwave-absorbing, machinable, and heat-dissipating plate. This work provides insight into the dielectric polarization loss mechanisms of nano-semiconductor/carbon composites and inspires the design of high-performance microwave absorption materials.

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Microstructures play a critical role to influence the polarization behavior of dielectric materials, which determines the electromagnetic response ability in gigahertz. However, the relationship between them, especially in the solid-solution structures is still absent. Herein, a series of (Ti1- y Nby )2 AlC MAX phase solid solutions with nano-laminated structures have been employed to illuminate the aforementioned problem. The relationship has been investigated by the lattice distortion constructed via tuning the composition from Ti to Nb in the M-site atomic layer. Experimental characterizations indicated that the dielectric response behaviors between declined conduction loss and boosted polarization loss can be well balanced by niobium atom manipulative solid-solution engineering, which is conducive to impedance matching and electromagnetic absorption performance. Theoretical calculation further proved that the origin of electric dipoles is ascribed to the charge density differences resulting from the altered microscopic atomic distribution. As a result, the Ti1.2 Nb0.8 AlC exhibits the mostly optimized microwave absorption property, in which a minimum reflection loss of -42 dB and an effective absorption bandwidth of 4.3 GHz under an ultra-thin thickness of 1.4 mm can be obtained. This work provides insight into the structural engineering in modifying electromagnetic response performance at gigahertz and which can be expanded to other solid-solution materials.

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Conduction and polarization losses are the main forms of dielectric loss, and regulating these mechanisms is key to obtaining favorable electromagnetic wave absorption performance. In this study, the conversion of graphite N and pyridine N in Cu-based metal-organic framework (MOF)-derived composites was adopted to modulate conduction and polarization losses by tuning the pyrolysis temperature and Cu salt concentration. The results show that increasing the pyrolysis temperature facilitates the conversion of pyridine N to graphite N, which is beneficial for conduction loss. Moreover, increasing the Cu concentration promotes the transformation of pyridine N to graphite N as well as, and then promotes the reverse conversion of graphite N to pyridine N, which is conducive to defect-induced polarization. The unique layered Cu/CuO/C composite obtained at 700 °C with a moderate Cu content exhibited the optimal performance with an effective absorption bandwidth of 5.5 GHz (11.6 âˆ¼ 17.1 GHz) at an ultra-thin thickness of 1.56 mm. This is owed to its favorable impedance matching, significant conduction loss, and polarization loss (defect-induced polarization and interfacial polarization). This study provides a novel strategy for regulating conduction and polarization losses.

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

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

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The prospect of graphene-based shielding materials in the form of fillers is limited by the cumbersome preparation of graphene. Herein, defect-tunable porous graphene prepared by carbothermal shock using low-value sucrose as a precursor is proposed as an effective shielding filler. The resultant porous graphene exhibits 32.5 dB shielding efficiency (SE) and 2.5-18 GHz effective bandwidth at a mass loading of 20 wt%, competing with the shielding performance of graphene fillers prepared by other methods. Particularly, defect-rich graphene synthesized by increasing voltage and prolonging time shows increased electromagnetic (EM) wave absorption, echoing the current concept of green shielding. In addition, the strategy of controlling the discharge conditions to improve the absorption by the shield is developed in the terahertz band. The average SE and reflection loss of the samples in the THz band (0.2-1.2 THz) exhibit 40.7 and 15.9 dB at filler loading of 5 wt%, respectively, achieving effective shielding and absorption of THz waves. This work paves a new way for low-cost preparation of graphene for EM interference shielding fillers. Meanwhile, it supplies a reference for the shielding research of the upcoming applications integrating multiple EM bands (such as sixth-generation based integrated sensing and communication).

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The increasing electromagnetic (EM) pollution that has seriously threatened human health and electronic devices urgently required high-performance absorbents toward attenuating EM wave (EMW). The combination of microstructure modulation and appropriate components regulation has proven to be a feasible strategy for improving the EMW absorption performance of absorbents. In this work, well-designed one-dimensional carbon nanofibers with macroporous structures and uniformly magnetic metal nanoparticles modification were prepared by the hard-template assisted electrospinning method followed by carbonization and template-elimination processes. The strong interfacial polarization loss and multireflection strengthened by the hollow structures and the magnetic loss induced by the introduced cobalt nanoparticles evidently enhanced the impedance matching level of the macroporous carbon nanofibers/cobalt nanoparticles (MCF/Co). As a result, MCF/Co composite offers broad absorption bandwidth (6.24 GHz) and strong electromagnetic wave absorption performance (-40.1 dB) at a thickness of 3.0 mm. This work inspires the rational one-dimensional macroporous carbon nanofibers design for new-generation EMW materials and provides an important research basis for the porous flexible EMW absorption materials.

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High-entropy oxides (HEOs), which incorporate multiple-principal cations into single-phase crystals and interact with diverse metal ions, extend the border for available compositions and unprecedented properties. Herein, a high-entropy-stabilized (Ca0.2 Sr0.2 Ba0.2 La0.2 Pb0.2 )TiO3  perovskite is reported, and the effective absorption bandwidth (90% absorption) improves almost two times than that of BaTiO3 . The results demonstrate that the regulation of entropy configuration can yield significant grain boundaries, oxygen defects, and an ultradense distorted lattice. These characteristics give rise to strong interfacial and defect-induced polarizations, thus synergistically contributing to the dielectric attenuation performance. Moreover, the large strains derived from the strong lattice distortions in the high-entropy perovskite offer varied transport for electron carriers. The high-entropy-enhanced positive/negative charges accumulation around grain boundaries and strain-concentrated location, quantitatively validated by electron holography, results in unusual dielectric polarization loss. This study opens up an effective avenue for designing strong microwave absorption materials to satisfy the increasingly demanding requirements of advanced and integrated electronics. This work also offers a paradigm for improving other interesting properties for HEOs through entropy engineering.

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It was well recognized that the penetrated electromagnetic (EM) wave could be dissipated by means of magnetic loss, polarization loss and conduction loss. In order to improve their loss capacities and take full advantage of flower-like geometrical morphology, in this study, we proposed a simple route for the production of flower-like core@shell structure NiO/Ni@C microspheres through the carbon thermal reaction using NiO microflowers as precursor. The obtained results revealed that our proposed strategy successfully synthesized the core@shell structure magnetic carbon-based multicomponent nanocomposites without destroying the geometrical morphology of precursor. By regulating the annealing temperature, the as-prepared NiO/Ni@C microspheres with different contents of Ni and degrees of graphitization could be selectively synthesized, which effectively boosted their magnetic loss, polarization loss and conduction loss capabilities. Therefore, the elaborately designed NiO/Ni@C microspheres displayed the superior microwave absorption performances including strong absorption capability, broad absorption bandwidth and thin matching thicknesses compared to the NiO precursor. In summary, our findings not only provided a simple route to design and synthesize flower-like core@shell structure magnetic carbon-based nanocomposites as novel microwave absorbers, but also presented an effective strategy to comprehensively improve their loss capacities.

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Carbon-based carbides have attracted tremendous attention for electromagnetic energy attenuation due to their adjustable dielectric properties, oxidation resistance, and good chemical stability. Herein, we reasonably regulate the growth of dopamine hydrochloride on the surface of the Mo-glycerate (Mo-GL) microsphere and then transform the resultant Mo-polydopamine (Mo-PD) microsphere into a dual-shell Mo2C/C (DS-Mo2C/C) microsphere in a high-temperature pyrolysis process under an inert atmosphere. It is found that the pyrolysis temperature plays an important role in the graphitization degree of the carbon matrix and internal architecture. The fabrication of a dual-shell structure can be propitious to the optimization of impedance matching, and the introduction of Mo2C nanoparticles also prompts the accumulation of polarization loss. When the pyrolysis temperature reaches 800 °C, the optimized composite of DS-Mo2C/C-800 exhibits good EM absorption performance in the frequency range of 2.0-18.0 GHz. DS-Mo2C/C-800's qualified bandwidth can reach 4.4 GHz at a matching thickness of 1.5 mm, and the integrated qualified bandwidth (QBW) even exceeds 14.5 GHz with a thickness range of 1.5-5.0 mm. The positive effects of the dual-shell structure and Mo2C nanoparticles on EM energy attenuation may render the DS-Mo2C/C microsphere as a promising candidate for lightweight and broad bandwidth EM absorption materials in the future.

Asunto(s)

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Demand for electromagnetic wave (EMW) absorbers continues to increase with technological advances in wearable electronics and military applications. In this study, a new strategy to overcome the drawbacks of current absorbers by employing the co-contribution of functional polymer frameworks and liquids with strong EMW absorption properties is proposed. Strongly polar water, dimethyl sulfoxide/water mixtures, and highly conductive 1-ethyl-3-methylimidazolium ethyl sulfate ([EMI][ES]) are immobilized in dielectrically inert polymer networks to form different classes of gels (hydrogels, organogels, and ionogels). These gels demonstrate a high correlation between their dielectric properties and polarity/ionic conductivity/non-covalent interaction of immobilized liquids. Thus, the EMW absorption performances of the gels can be precisely tuned over a wide range due to the diversity and stability of the liquids. The prepared hydrogels show good shielding performance (shielding efficiency > 20 dB) due to the high dielectric constants, while organogels with moderate attenuation ability and impedance matching achieve full-wave absorption in X-band (8.2-12.4 GHz) at 2.5 ± 0.5 mm. The ionogels also offer a wide effective absorption bandwidth (10.79-16.38 GHz at 2.2 mm) via prominent ionic conduction loss. In short, this work provides a conceptually novel platform to develop high-efficient, customizable, and low-cost functional absorbers.