Microwave absorbing materials (MAMs) are playing an increasingly essential role in the development of wireless communications, high-power electronic devices, and advanced target detection technology. MAMs with a broad-bandwidth response are particularly important in the area of communication security, radiation prevention, electronic reliability, and military stealth. Although considerable progress has been made in the design and preparation of MAMs with a broad-bandwidth response, a number of challenges still remain, and the structure–function relationship of MAMs is still far from being completely understood. Herein, the advances in the design and research of MAMs with a broad-bandwidth response are outlined. The main strategies for expanding the effective absorption bandwidth of MAMs are comprehensively summarized considering three perspectives: the chemical combination strategy, morphological control strategy, and macrostructure control strategy. Several important results as well as design principles and absorption mechanisms are highlighted. A coherent explanation detailing the influence of the chemical composition and structure of various materials on the microwave absorption properties of MAMs is provided. The main challenges, new opportunities, and future perspectives in this promising field are also presented.

Metallic iron particles are of great potential for microwave absorption materials due to their strong magnetic loss ability. However, the oxidation susceptibility of metallic iron particles in the atmospheric environment is regarded as a major factor causing performance degradation. Although many efforts have been developed to avoid their oxidation, whether partial surface oxidized iron particles can improve the microwave absorbing performance is rarely concerned. In order to explore the effect of partial surface oxidation of iron on its properties, the designed yolk–shelled (Fe/FeO_x)@C composites with multiple heterointerfaces were synthesized via an in-situ polymerization and a finite reduction–oxidation process of Fe₂O₃ ellipsoids. The performance enhancement mechanisms of Fe/FeO_x heterointerfaces were also elaborated. It is demonstrated that the introduction of Fe-based heterogeneous interfaces can not only enhance the dielectric loss, but also increase the imaginary part of the permeability in the higher frequency range to strengthen the magnetic loss ability. Meanwhile, the yolk–shell structure can effectively improve impedance matching and enhance microwave absorption performances via increasing multiple reflection and scattering behaviors of incident microwaves. Compared to Fe@C composite, the effective absorption (reflection loss (RL) < −10 dB) bandwidth of the optimized (Fe/FeO_x)@C-2 increases from 5.7 to 7.3 GHz (10.7–18.0 GHz) at a same matching thickness of 2 mm, which can completely cover Ku-band. This work offers a good perspective for the enhancement of magnetic loss ability and microwave absorption performance of Fe-based microwave absorption materials with promising practical applications.

Platinum (Pt) is an outstanding catalyst for many important industrial products. Because of its high cost and scarce reserves, it is very important to improve the performance of Pt catalysts. As the metal nanocrystals (NCs) with high-index surfaces usually show very good catalytic activity because of their high density of atomic steps and kinks, the preparation of Pt NCs with high-index facets has become a very important and hot research topic recently. In this article, we report a facile synthesis of high-yield Pt NCs with a series of {hkk} high-index facets including {211} and {411} via a solvothermal method using Pt(II) acetylacetonate as the Pt source, 1-octylamine as the solvent and capping agent, and formaldehyde as an additional surface structure regulator. Multipod Pt NCs with dominant {211} side surfaces were produced without formaldehyde, while concave Pt NCs with dominant {411} surfaces formed under the influence of formaldehyde. By analyzing the products by IR spectroscopy, we found the presence of CO on the surface of concave Pt NCs with {411} surfaces prepared from the solution containing formaldehyde. It was concluded that amine mainly stabilized the monoatomic step edges, resulting in the {211} exposed surface; with addition of formaldehyde, it decomposed into CO, leading to the formation of {411} surfaces by the additional adsorption of the CO on the {100} terraces. In addition, it was found that the as-prepared Pt NCs with high-index {211} and {411} surfaces exhibited much better catalytic activity in the electro-oxidation of ethanol than a commercial Pt/C catalyst or Pt nanocubes with low-index {100} surfaces, and the catalytic activities of Pt crystal facets decreased in the sequence {411} > {211} > {100}.