Constructing Ni12P5/Ni2P Heterostructures to Boost Interfacial Polarization for Enhanced Microwave Absorption Performance

Reinforced Interfacial Polarization in Composited High-Entropy-Alloy Nanoparticles/Graphene for Efficient Microwave Absorption

High-entropy alloys, particularly nanoparticles (HEANPs) composed of multiple magnetic elements, have shown promise as efficient agents to address electromagnetic challenges. However, their limited magnetic loss capabilities can be inadequate when confronted with dielectric loss requirements. Herein, using a carbothermal reduction strategy, a composite microwave absorber consisting of HEANPs (CoNiCuFeMnPbMgAl) and graphene sheets (HEANPs/G), in which the graphene sheets are incorporated to mitigate dielectric limitations, is synthesized. Benefiting from the natural resonance and electric dipole polarization induced by HEANPs and graphene defects respectively, an excellent reflection loss (RL) of less than -30 dB is achieved in all samples. Notably, both the experimental and first-principles results indicate that the interface polarization can be reinforced by increasing the charge transfer at the interface to further improve the absorption behavior, which is attributed to the enhanced electrical resistivity caused by the composing element species gradually increasing to eight. Consequently, the optimized octonary HEANPs/G achieves an RL value of -62.30 dB (7.20 GHz, 3.13 mm) with a broad effective absorption bandwidth of 4.16 GHz. This study establishes a relationship between multiple loss behaviors and microwave absorption capabilities in high-entropy composites, while also providing a pathway to compensate for the shortcomings of single magnetic loss materials.

Ni12P5 and Ni12P5-rGO for multifunctional electrocatalyst and supercapacitor application

Transition metal phosphides are crucial for various environmental and energy applications. In this study, porous Ni12P5 and Ni12P5-rGO were synthesized using a one-step solvothermal method. Red phosphorus served as the phosphorus source, while ethylene glycol acted as a capping agent to promote the formation of nanomaterials within a nitrogen-rich atmosphere. The catalytic performance of these materials was evaluated through their hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and capacitance properties. Notably, Ni12P5-rGO exhibited Tafel slopes of 66 mV/dec for OER and 33 mV/dec for HER, indicating enhanced charge transfer efficiency compared to Ni12P5, which showed slopes of 78 mV/dec and 102 mV/dec, respectively. This improvement suggests that Ni12P5-rGO facilitates faster electron transfer, resulting in superior catalytic performance. Additionally, the synergistic effect of reduced graphene oxide (rGO) contributes to improved charge storage capabilities. The Ni12P5-rGO demonstrated a specific capacitance of 192 F/g, significantly higher than the 110 F/g observed for Ni12P5 at a current density of 1 A/g. Remarkably, these materials maintained their capacity over 5000 cycles, achieving a commendable 98 % coulombic efficiency. These findings highlight the potential of Ni12P5-rGO as an effective material for energy conversion and storage applications, showcasing its promising role in advancing the efficiency of related technologies.

Construction of 3D Fibonacci Cauliflower-Like NiCo2S4/Expanded Graphite Heterogeneous Structures for Enhanced Electromagnetic Wave Absorption

Highly efficient electromagnetic wave (EMW)-absorbing multicomposites can be fabricated by constructing particular structures using suitable components. Expanded graphite (EG) has a 3D, low-density porous structure; however, it suffers from poor impedance matching and EMW absorption properties. Based on this information, in the present study, NiCo2S4 components with different morphologies are successfully loaded onto a 3D EG surface using a facile microwave solvothermal method to achieve a synergistic effect between the different components. The NiCo2S4 content is adjusted to alter the compositional morphology and electromagnetic parameters of the composites to achieve impedance-matching and obtain excellent EMW absorption properties. The heterogeneous interface between EG and NiCo2S4 induces an inhomogeneous spatial charge distribution and enhances interfacial polarization. The defects in the material and oxygen-containing groups induce dipole polarization, which enhances the polarization-relaxation process of the composites. The 3D porous heterostructure of the "Fibonacci cauliflower"-shaped NiCo2S4/EG composites results in an optimal reflection loss of -64.93 dB at a filler rate of only 14 wt.%. Analysis of the synergistic conduction loss and polarization loss mechanisms in carbon-based materials with heterogeneous interfaces has led to the development of excellent EMW absorption materials.

Progress in microwave absorbing materials: A critical review

Microwave-absorbing materials play a significant role in various applications that involve the attenuation of electromagnetic radiation. This critical review article provides an overview of the progress made in the development and understanding of microwave-absorbing materials. The interaction between electromagnetic radiation and absorbing materials is explained, with a focus on phenomena such as multiple reflections, scattering, and polarizations. Additionally, types of losses that affect the performance of microwave absorbers are also discussed, including dielectric loss, conduction loss, relaxation loss, magnetic loss, and morphological loss. Each of these losses has different implications for the effectiveness of microwave absorbers. Further, a detailed review is presented on various types of microwave absorbing materials, including carbonaceous materials, conducting polymers, magnetic materials, metals and their composites, 2D materials (such as MXenes and 2D-transition metal dichalcogenides), biomass-derived materials, carbides, sulphides, phosphides, high entropy (HE) materials and metamaterials. The characteristics, advantages, and limitations of each material are examined. Overall, this review article highlights the progress achieved in the field of microwave-absorbing materials. It underlines the importance of optimizing different types of losses to enhance the performance of microwave absorbers. The review also recognizes the potential of emerging materials, such as 2D materials and high entropy materials, in further advancing microwave-absorbing properties.

Fe2P nanoparticle-decorated carbon nanofiber composite towards lightweight and highly efficient microwave absorption

An Fe2P nanoparticle (Fe2P NP)-decorated carbon nanofiber (represented as Fe2P@CNF) composite was in situ prepared by electrospinning and subsequent high-temperature treatment. Benefitting from the synergy effect between Fe2P NPs and CNFs, as well as improved interface polarization and impedance matching, the Fe2P@CNF composite exhibits excellent microwave absorption performance relative to pure CNFs, in which the Fe2P@CNF composite with a fill loading of only 10 wt% possesses a minimum reflection loss (RL) of -49.2 dB at 3.0 mm and a maximum effective absorption bandwidth of 6.0 GHz at 2.2 mm. Therefore, this work provides a promising approach for the design and synthesis of an Fe2P@CNF composite with high-performance microwave absorption.

Engineering Phase to Reinforce Dielectric Polarization in Nickel Sulfide Heterostructure for Electromagnetic Wave Absorption

Engineering phase transition in micro-nanomaterials to optimize the dielectric properties and further enhance the electromagnetic microwave absorption (EMA) performance is highly desirable. However, the severe synthesis conditions restrict the design of EMA materials featuring controllable phases, which hinders the tunability of effective absorption bandwidth (EAB) and leads to an unclear loss mechanism. Herein, a seed phase decomposition-controlled strategy is proposed to induct nickel sulfide (NiSx ) absorbers with controllable phases and hollow sphere nature. Transmission electron microscopy holography and theoretical calculations evidence that the reconstruction of atoms in phase transition induces numerous heterogeneous interfaces and lattice defects/sulfur vacancies to cause varied work functions and local electronic redistribution, which contributes to reinforced dielectric polarization. As a result, the optimized NiS2 /NiS heterostructure enables enhanced EM attenuation capability with a wide EAB of 5.04 GHz at only 1.6 mm, compared to that of NiS2 and NiS. Moreover, the correlation between EAB and NiS phase content is demonstrated as the "volcano" feature. This study on the concept of phase transition of micro-nanomaterials can offer a novel approach to constructing highly efficient absorbers for EMA and other functionalities.

Controlled Synthesis of MOF-Derived Nano-Microstructure toward Lightweight and Wideband Microwave Absorption

Correlating metal-organic framework (MOF) synthesis processes and microwave absorption (MA) enhancement mechanisms is a pioneer project. Nevertheless, the correlation process still relies mainly on empirical doctrine, which hardly corresponds to the specific mechanism of the effect on the dielectric properties. Hereby, after the strategy of modulation of protonation engineering and solvothermal temperature in the synthesis route, the obtained sheet-like self-assembled nanoflowers were constructed. Porous structures with multiple heterointerfaces, abundant defects, and vacancies are obtained by controlled design of the synthesis procedure. The rearrangement of charges and enhanced polarization can be promoted. The designed electromagnetic properties and special nano-microstructures of functional materials have significant impact on their electromagnetic wave energy conversion effects. As a consequence, the MA performance of the samples has been enhanced toward broadband absorption (6.07 GHz), low thickness (2.0 mm), low filling (20%), and efficient loss (-25 dB), as well as being suitable for practical environmental applications. This work establishes the connection between the MOF-derived materials synthesis process and the MA enhancement mechanism, which provides insight into various microscopic microwave loss mechanisms.

Surface engineering of carbon-coated cobalt-doped nickel phosphides bifunctional electrocatalyst for boosting 5-hydroxymethylfurfural oxidation coupled with hydrogen evolution

Multiple surface/interface engineering is an effective approach to develop efficient electrocatalysts for promoting the practical application of electrocatalysis and achieving carbon neutrality. Herein, a deep eutectic liquid precursor containing phosphorus was designed. The self-supported three-dimensional (3D) cobalt-doped Ni12P5/Ni3P nanowire networks coated with a thin layer of carbon (Co-NixP@C) were prepared by using an in-situ one-step pyrolysis method. The as-obtained Co-NixP@C hybrid possesses a superaerophobic/superhydrophilic surface, which could promote electrolyte diffusion and enhance bubble release. Density functional theory (DFT) calculations reveal that Co-doping in NixP@C can promote the adsorption and activation of 5-hydroxymethylfurfural (HMF) molecules, and optimize the energy barrier of H* absorption. The self-supported Co-NixP@C was used as an efficient bifunctional electrocatalyst for HMF oxidation coupled with hydrogen evolution reaction (HER) in a 1.0 M KOH solution. A nearly 100 % yield of 2,5-furandicarboxylic acid (FDCA) was achieved. The self-supported Co-NixP@C displayed high activity and stability for both HER and HMF conversion. The HMF oxidation coupled with HER can be efficiently driven by a 1.5 V commercial photovoltaic panel under sunlight. This study lays the foundation for large-scale industrialization in sustainable fine-chemical and energy engineering.

1D CNT-Expanded 3D Carbon Foam/Si3N4 Sandwich Heterostructure: Utilizing the Polarization Compensation Effect for Keeping Stable Electromagnetic Absorption Performance at Elevated Temperature

Modern electromagnetic (EM) absorbing materials (EAMs) are experiencing a revolution triggered by advanced information technology. Simultaneously, the diverse harsh EM application scenarios entail a more stringent appeal of practicability to EAMs, especially under high-temperature conditions. Therefore, exploring EAMs with both excellent absorbing performance and practicability at elevated temperatures is necessary. Herein, a novel 3D porous carbon foam/carbon nanotubes@Si₃N₄ (CF/CNTs@Si₃N₄) heterostructure was constructed by the chemical vapor infiltration process. The optimally grown 1D CNTs embedded in 3D CF/Si₃N₄ are utilized to provide abundant nanointerface coupling effects to compensate for the excessive increase in the conductive loss during rising temperature to realize a self-adjustment in response to high temperature. A high-efficiency EM absorption over a wide temperature range from 25 to 480 °C was achieved (with a ≥90% absorbing ratio covering the whole X-band). In addition, the Si₃N₄ coating can improve the thermal stability of the carbon matrix and maintain the tailored inner structure. Multiple investigations into other environmental adaptabilities also exhibited the application perspective of such a heterostructure. This work points out a new strategy for preparing designable, efficient, and high-temperature applicable EAMs, promoting the diverse development of electronic devices.

Sequential Phase Conversion-Induced Phosphides Heteronanorod Arrays for Superior Hydrogen Evolution Performance to Pt in Wide pH Media

Developing an efficient and non-precious pH-universal hydrogen evolution reaction electrocatalyst is highly desirable for hydrogen production by electrochemical water splitting but remains a significant challenge. Herein, a hierarchical structure composed of heterostructured Ni₂ P-Ni₁₂ P₅ nanorod arrays rooted on Ni₃ S₂ film (Ni₂ P-Ni₁₂ P₅ @Ni₃ S₂ ) via a simultaneous corrosion and sulfidation is built followed by a phosphidation treatment toward the metallic nickel foam. The combination of theoretical calculations with in/ex situ characterizations unveils that such a unique sequential phase conversion strategy ensures the strong interfacial coupling between Ni₂ P and Ni₁₂ P₅ as well as the robust stabilization of 1D heteronanorod arrays by Ni₃ S₂ film, resulting in the promoted water adsorption/dissociation energy, the optimized hydrogen adsorption energy, and the enhanced electron/proton transfer ability accompanied with an excellent stability. Consequently, Ni₂ P-Ni₁₂ P₅ @Ni₃ S₂ /NF requires only 32, 46, and 34 mV overpotentials to drive 10 mA cm^-2 in 1.0 m KOH, 0.5 m H₂ SO₄ , and 1.0 m phosphate-buffered saline electrolytes, respectively, exceeding almost all the previously reported non-noble metal-based electrocatalysts. This work may pave a new avenue for the rational design of non-precious electrocatalysts toward pH-universal hydrogen evolution catalysis.

Enhanced interfacial polarization of biomass-derived porous carbon with a low radar cross-section

Ultra-thin microwave absorbers have been urgently demanded for electromagnetic applications in recent years. Herein, porous carbon with a "flower cluster" microstructure was synthesized from biomass waste (mango seeds) by a facile activation and carbonization method. The novel structure reduced the density and also improved the impedance matching, dipole polarization, and provided many carbon matrix-air interfaces for interfacial polarization, resulting in superior microwave absorption performance. At an ultra-thin thickness of 1.5 mm, extraordinary microwave absorption was achieved, with a reflection loss (RL) of -42 dB. The effective absorption bandwidth reached 4.2 GHz. The RL can be further improved to -68.4 dB by adjusting the amount of activator to manipulate the structure of porous carbon. In addition, from the simulated radar scattering results, the maximum reduction in the radar cross-section (RCS) reached 30.4 dBm², which can greatly reduce the probability of equipment being detected by radar. This work provides a low-cost and high-performance microwave absorber for electromagnetic stealth technologies.

The Preparation and Electrochemical Pseudocapacitive Performance of Mutual Nickel Phosphide Heterostructures

Transition metal phosphide composite materials have become an excellent choice for use in supercapacitor electrodes due to their excellent conductivity and good catalytic activity. In our study, a series of nickel phosphide heterostructure composites was prepared using a temperature-programmed phosphating method, and their electrochemical performance was tested in 2 mol L−1 KOH electrolyte. Because the interface effect can increase the catalytic active sites and improve the ion transmission, the prepared Ni2P/Ni3P/Ni (Ni/P = 7:3) had a specific capacity of 321 mAh g−1 under 1 A g−1 and the prepared Ni2P/Ni5P4 (Ni/P = 5:4) had a specific capacity of 218 mAh g−1 under 1 A g−1. After the current density was increased from 0.5 A g−1 to 5 A g−1, 76% of the specific capacity was maintained. After 7000 cycles, the capacity retention rate was above 82%. Due to the phase recombination effect, the electrochemical performance of Ni2P/Ni3P/Ni and Ni2P/Ni5P4 was much better than that of single-phase N2P. After assembling the prepared composite and activated carbon into a supercapacitor, the Ni2P/Ni3P/Ni//AC had an energy density of 22 W h kg−1 and a power density of 800 W kg−1 and the Ni2P/Ni5P4//AC had an energy density of 27 W h kg−1 and a power density of 800 W kg−1.

Ni Flower/MXene-Melamine Foam Derived 3D Magnetic/Conductive Networks for Ultra-Efficient Microwave Absorption and Infrared Stealth

The development of multifunctional and efficient electromagnetic wave absorbing materials is a challenging research hotspot. Here, the magnetized Ni flower/MXene hybrids are successfully assembled on the surface of melamine foam (MF) through electrostatic self-assembly and dip-coating adsorption process, realizing the integration of microwave absorption, infrared stealth, and flame retardant. Remarkably, the Ni/MXene-MF achieves a minimum reflection loss (RL_min) of - 62.7 dB with a corresponding effective absorption bandwidth (EAB) of 6.24 GHz at 2 mm and an EAB of 6.88 GHz at 1.8 mm. Strong electromagnetic wave absorption is attributed to the three-dimensional magnetic/conductive networks, which provided excellent impedance matching, dielectric loss, magnetic loss, interface polarization, and multiple attenuations. In addition, the Ni/MXene-MF endows low density, excellent heat insulation, infrared stealth, and flame-retardant functions. This work provided a new development strategy for the design of multifunctional and efficient electromagnetic wave absorbing materials.

Quinary High-Entropy-Alloy@Graphite Nanocapsules with Tunable Interfacial Impedance Matching for Optimizing Microwave Absorption

Designing heterogeneous interfaces and components at the nanoscale is proven effective for optimizing electromagnetic wave absorption and shielding properties, which can achieve desirable dielectric polarization and ferromagnetic resonances. However, it remains a challenge for the precise control of components and microstructures via an efficient synthesis approach. Here, the arc-discharged plasma method is proposed to synthesize core@shell structural high-entropy-alloy@graphite nanocapsules (HEA@C-NPs), in which the HEA nanoparticles are in situ encapsulated within a few layers of graphite through the decomposition of methane. In particular, the HEA cores can be designed via combinations of various transition elements, presenting the optimized interfacial impedance matching. As an example, the FeCoNiTiMn HEA@C-NPs obtain the minimum reflection loss (RL_min ) of -33.4 dB at 7.0 GHz (3.34 mm) and the efficient absorption bandwidth (≤-10 dB) of 5.45 GHz ranging from 12.55 to 18.00 GHz with an absorber thickness of 1.9 mm. The present approach can be extended to other carbon-coated complex components systems for various applications.

Heterointerface Engineering in Electromagnetic Absorbers: New Insights and Opportunities

Electromagnetic (EM) absorbers play an increasingly essential role in the electronic information age, even toward the coming "intelligent era". The remarkable merits of heterointerface engineering and its peculiar EM characteristics inject a fresh and infinite vitality for designing high-efficiency and stimuli-responsive EM absorbers. However, there still exist huge challenges in understanding and reinforcing these interface effects from the micro and macro perspectives. Herein, EM response mechanisms of interfacial effects are dissected in depth, and with a focus on advanced characterization as well as theoretical techniques. Then, the representative optimization strategies are systematically discussed with emphasis on component selection and structural design. More importantly, the most cutting-edge smart EM functional devices based on heterointerface engineering are reported. Finally, current challenges and concrete suggestions are proposed, and future perspectives on this promising field are also predicted.

Novel bimetallic MOF derived hierarchical Co@C composites modified with carbon nanotubes and its excellent electromagnetic wave absorption properties

In the severe electromagnetic wave pollution situation, the absorbers must meet the requirements of lightweight, strong absorption, thin thickness and wide band. Under such a circumstance, it is of great significance to construct reasonable structure and composition for excellent electromagnetic wave absorption. Therefore, the Co/C composites anchored with carbon nanotubes (Co@CNTs) have been successfully prepared by rationally regulating the growth of bimetallic MOF and subsequent pyrolysis process. It is revealed that the conduction loss and polarization loss caused by the carbon nanotubes with different lengths and densities and the porosity of the composites are together responsible for the attenuation of electromagnetic wave. As expected, the hierarchical Co@CNTs composites showed a strong reflection loss of -76.6 dB and a broad effective absorption bandwidth of 6.2 GHz through the improvement of impedance matching and electromagnetic wave absorption ability. Herein, this work presents a strategy for the development of composites as promising electromagnetic wave absorbent.

Enhanced Microwave Absorbing Ability of Carbon Fibers with Embedded FeCo/CoFe2O4 Nanoparticles

In the face of increasingly severe electromagnetic (EM) wave pollution, the research of EM wave absorbing materials is an effective solution. To reduce the density of traditional absorbing materials, in this work, FeCo/CoFe₂O₄/carbon nanofiber composites were successfully prepared by electrospinning for the EM wave attenuation application. Benefiting from the loss ability of interface polarization, dipole polarization, and magnetic loss, the composites obtained a bandwidth of 5.0 GHz at a 1.95 mm thickness and an absorption peak of -52.3 dB. More importantly, the radar cross section (RCS) reduction of composite coatings calculated by ANSYS Electronics Desktop 2018 (HFSS) can reach 34.5 dBm², and the RCS value is almost less than -10 dBm² when the incident angle is greater than 20°, demonstrating great scattering ability of the material coating to EM waves. This work, combined with the exploration of the mechanism and the simulation analysis of the absorbing coating, will be of significance for the development of absorbing materials.

Constructing a nitrogen-doped carbon and nickel composite derived from a mixed ligand nickel-based a metal-organic framework toward adjustable microwave absorption

The rational design of nanostructures for absorbers has great potential in the microwave absorption field. In this work, a mixed ligand nickel metal-organic framework (ML-Ni MOF) was first prepared by the self-assembly of pyrazine and 1,3,5-benzenetricarboxylic acid with nickel ions. Then, the as-prepared ML-Ni MOF was used as a precursor to fabricate a nitrogen-doped carbon and nickel composite (ML-Ni/C). With the molar ratio of pyrazine and 1,3,5-benzenetricarboxylic acid of 1 : 1, the flower-like ML-Ni MOF was obtained. After pyrolysis, the ML-Ni MOF-derived ML-Ni/C composite showed an optimal reflection loss value of -65.33 dB with a thickness of 2.4 mm and a corresponding effective absorbing bandwidth (EAB, RL ≤ -10 dB) of 5.1 GHz. Besides, the broadest EAB of 7.6 GHz was achieved when the thickness was about 2.8 mm. This strategy paves a new way to design novel MOFs as precursors for fabricating absorbers.

Multiple interface-induced evolution of electromagnetic patterns for efficient microwave absorption at low thickness

Mo-Ni₂P/rGO composites with heterojunction structures were successfully prepared by phosphating NiMoO₄/rGO precursors at a specific temperature, which exhibit excellent microwave absorption performances at low thickness.