Magnetic/dielectric composite materials with numerous heterointerfaces are highly promising functional materials, which are widely applied in the fields of electromagnetic wave absorption. Constructing heterogeneous structure is beneficial to further enhance the microwave absorption performance of composite materials. However, the process of constructing multi-heterogeneous interfaces is extremely complex. In this work, hollow porous FeCo/Cu/CNTs composite microspheres are prepared by the simple spray drying method and subsequently two-step annealing treatment, which possess abundant heterogeneous interfaces, unique three-dimensional conductive network and magnetic coupling network. This unique structure is beneficial to improving the ability of dielectric loss and magnetic loss, and then achieving an excellent microwave absorption performance. The prepared FeCo/Cu/CNTs-1 composite microspheres maintain a minimum reflection loss (RL) of –48.1 dB and a maximum effective absorption bandwidth of 5.76 GHz at a thickness of 1.8 mm. Generally, this work provides a new idea for designing multi-heterogeneous of microwave absorbing materials.

Development of high-performance microwave absorption materials (MAM) with stabilized magnetic properties at high temperatures is specifically essential but remains challenging. Moreover, the Snoke's limitation restrains the microwave absorption (MA) property of magnetic materials. Modulating alloy components is considered an effective way to solve the aforementioned problems. Herein, a hollow medium-entropy FeCoNiAl alloy with a stable magnetic property is prepared via simple spray-drying and two-step annealing for efficient MA. FeCoNiAl exhibited an ultrabroad effective absorption band (EAB) of 5.84 GHz (12.16–18 GHz) at a thickness of just 1.6 mm, revealing an excellent absorption capability. Furthermore, the MA mechanism of FeCoNiAl is comprehensively investigated via off-axis holography. Finally, the electromagnetic properties, antioxidant properties, and residual magnetism at high temperatures of FeCoNiAl alloys are summarized in detail, providing new insights into the preparation of MAM operating at elevated temperatures.

The design and optimization of one-dimension (1D) magnetic material are of great importance for the energy conversion, storage and spin electron devices, which remain a huge challenge. Herein, 1D porous Fe₃O₄ nanotubes (NTs) have been fabricated via a combined process of electrospinning and calcination. In the electrospinning precursors, by regulating the content ratio between two types of polyvinyl pyrrolidone with different molecular weight, porous Fe₃O₄ NTs with vortex-domain configuration have been fabricated. Based on the unique 1D nanotube structure encapsulated with multi-domains, the composite Fe₃O₄ NTs exhibit high complex permeability (μʹ, μʺ) values, and hold both strong magnetic storage and dissipation capacity. Our Fe₃O₄ NTs exhibit excellent microwave absorption (MA) performance with the maximum reflection loss value of −57.1 dB and the efficient absorption bandwidth of 12.0 GHz. The generated magnetic vortices make the crucial contribution to the spin-wave resonance which improves the MA dissipation under high-frequency. Related magnetic flux line distribution and magnetic domain moment were confirmed by the electron holography and micro-magnetic simulation, respectively, providing the deep insight to the microwave absorption mechanism.

Maximizing wave function overlap (WFO) within type-II superlattices (T2SL) is demonstrated to be important for improving their photoelectric properties, such as optical transition strength and quantum efficiency, which, however, remains a great challenge for now. Herein, the dual strategy of modulating growth temperature and inserting ultrathin AlAs barrier into the AlSb layers is presented to enhance the WFO in InAs/AlSb T2SL. The charge distributions and strain states indicate that moderate growth temperature of 470 °C promotes the As–Sb exchange at AlSb-on-InAs (AOI) interfaces, which would introduce skew of energy band structure towards InAs-on-AlSb (IOA) interface. Such band structure could drive electrons and holes to the IOA interfaces simultaneously, thus resulting in the enhanced WFO. On this basis, insertion of relatively thick (0.3 nm) AlAs layers is found to squeeze more holes towards adjacent interfaces, boosting the WFO further. The InAs/AlSb superlattices with optimized WFO reveal better optical performance, where the peak intensity shows 50% improvement in the PL spectra than the original one. Moreover, a dual-miniband radiative transition mechanism appears in the InAs/AlSb superlattice with relatively thick AlAs intercalation, which helps broaden the wavelength range of the superlattice.

Cobalt diselenide (CoSe₂) hierarchical clew-like structure is synthesized via a dual-surfactant templated hydrothermal process, and for the first time, its microwave absorption capability has been established. Specifically, the as-synthesized hierarchical interconnected structure is assembled by numerous dense nanobelts. Meticulous tuning of the synthetic conditions which could influence the hierarchical architecture indicates that, in this system, cetyltrimethylammonium bromide (CTAB) plays a dominate role of "balling" while protonated diethylenetriamine (DETA) plays the role of "stringing" . As a novel absorbent, the microwave absorption performance of CoSe₂ microstructure is evaluated in 2-18 GHz band. Particularly, 3D hierarchical CoSe₂ microclews exhibit superior minimum reflection loss of -26.93 dB at 7.28 GHz and effective absorption bandwidth of 3.72 GHz, which are ~120% and ~104% higher than those of simple CoSe₂ nanosheets, respectively. Such drastic enhancement could be attributed to the large specific surface area, and more dissipation channels and scattering sites enabled by the unique clew-like microstructure. The versatile dual-surfactant templated assembly of hierarchical CoSe₂ microstructure, along with its appreciable dielectric microwave absorption performance, provides new inspirations in developing novel microwave absorbents for mitigation of electromagnetic pollution.

As the proportion of interfaces increases rapidly in nanomaterials, properties and quality of interfaces hugely impact the performance of advanced semiconductors. Here, the effect of interfaces is explored by comparatively studying two InAs/AlSb superlattices with and without the thin InAsSb layers inserted inside each InAs layers. Through strain mapping, it indicates that the addition of interfaces leads to an increase of local strain both near interfaces and inside layers. Meantime, owing to the creation of hole potential wells within the original electron wells, the charge distribution undergoes an extra electron-hole alternating arrangement in the structure with inserted layers than the uninserted counterpart. Such a feature is verified to enhance electron-hole wave function overlap by theoretical simulations, which is a must for better optical performance. Furthermore, with an elaborate design of the inserted layers, the wave function overlap could be boosted without sacrificing other key device performances.

Developing efficient and low-cost electrocatalysts for oxygen evolution reaction (OER) with high electrochemical activity and durability for diverse renewable and sustainable energy technologies remains challenging. Herein, an ultrasonic-assisted and coordination modulation strategy is developed to construct sandwich-like metal-organic framework (MOF) derived hydroxide nanosheet (NS) arrays/graphene oxide (GO) composite via one-step self-transformation route. Inducing from unsteady state, the dodecahedral ZIF-67 with Co²⁺ in tetrahedral coordination auto-converts into defect-rich ultrathin layered hydroxides with the interlayered ion NO₃^-. The self-transforming α-Co(OH)₂/GO nanosheet arrays from ZIF-67 (Co(OH)₂-GNS) change the coordination mode of Co²⁺ and bring about the exposure of more metal active sites, thereby enhancing the spatial utilization ratio within the framework. As monometal-based electrocatalyst, the optimized Co(OH)₂-GNS exhibits remarkable OER catalytic performance evidenced by a low overpotential of 259 mV to achieve a current density of 10 mA·cm^-2 in alkaline medium, even exceeding commercial RuO₂. During the oxygen evolution process, electron migration can be accelerated by the interfacial/in-plane charge polarization and local electric field, corroborated by the off-axis electron holography. Density functional theory (DFT) calculations further studied the collaboration between ultrathin Co(OH)₂ NS and GO, which leads to lower energy barriers of intermediate products and greatly promotes electrocatalytic property.

Design and fabrication of cost-effective transition metal and their oxides-based nanocomposites are of paramount significance for metal-air batteries and water-splitting. However, the traditional optimized designs for nanostructure are complicated, low-efficient and underperform for wide-scale applications. Herein, a novel hierarchical framework of hollow Ni/NiFe₂O₄-CNTs composite microsphere forcibly-assembled by zero-dimensional (0D) Ni/NiFe₂O₄ nanoparticle (< 16 nm) and one-dimensional (1D) self-supporting CNTs was fabricated successfully. Benefitted from the unique nanostructure, such monohybrids can achieve remarkable oxygen evolution reaction (OER) performance in alkaline media with a low overpotential and superior durability, which exceeds most of the commercial catalysts based on IrO₂/RuO₂ or other non-noble metal nanomaterials. The enhanced OER performance of Ni/NiFe₂O₄-CNTs composite is mainly ascribed to the increased catalytic activity and the optimized conductivity induced by the effects of strong hierarchical coupling and charge transfers between CNTs and Ni/NiFe₂O₄ nanoparticles. These effects are greatly boosted by the polarized heterojunction interfaces confirmed by electron holography. The density functional theory (DFT) calculation indicates the epitaxial Ni further enriches the intrinsic electrons contents of NiFe₂O₄ and thus accelerates absorption/desorption kinetics of OER intermediates. This work hereby paves a facile route to construct the hollow composite microsphere with excellent OER electrocatalytic activity based on non-noble metal oxide/CNTs.

Faster response benefits the high-performance of magnetic material in various live applications. Hence, enhancing response speed toward the applied field via engineering advantages in structures is highly desired. In this paper, the precise synthesis of Co nanochain with the tunable length-diameter ratio is realized via a magnetic-field-guided assembly approach. The Co nanochain exhibits enhanced microwave absorption performance (near to -60 dB, layer thickness 2.2 mm) and broader effective absorption bandwidth (over 2/3 of total S, C, X, Ku bands). Furthermore, the simulated dynamic magnetic response reveals that the domain motion in 1D chain is faster than that in 0D nanoparticle, which is the determining factor of magnetic loss upgrade. Meanwhile, based on the controllable magnetic field experiment via in situ transmission electron microscopy, the association between magnetic response and microstructure is first present at the nanometer-level. The real and imaginary parts of relative complex permeability are determined by the domain migration confined inside Co nanochain and the magnetic flux field surrounded outside Co nanochain, respectively. Importantly, these findings can be extended to the novel design of microwave absorbers and promising candidates of magnetic carriers based on 1D structure.

Carbon-sulfur composites have drawn increasing interest in various fields including electrocatalysis because of their unique structures. However, carbon-sulfur composite with tiny sulfur nanocrystals has still received little attention. Herein, hollow porous carbon sphere-sulfur composite (HPCS-S) which possesses excellent electrochemical performance towards H₂O₂ has been prepared for the first time via a simple silica template method. The 2–5 nm sulfur nanocrystals being restricted in the channel of the hollow porous carbon spheres are under a strong compressive stress, which was further confirmed by high-resolution transmission electron microscopy (HRTEM) and GPA. The HPCS-S nanocrystals show better conductivity than amorphous sulfur clusters because of the reduction of the steric hindrance which efficiently promotes the electron transportation. Consequently, the higher activity and selectivity towards the 2e^- oxygen reduction reaction (ORR) to H₂O₂ in alkaline solution was obtained. The H₂O₂ selectivity rises from 20% to over 70% after the sulfur addition and the H₂O₂ production rate achieves 183.99 mmol·g_catalyst^-1 with the Faradaic efficiency of 70%. Furthermore, performance enhancement mechanism was also investigated using the density functional theory (DFT) calculations. After the introducing of sulfur nanocrystals, the appearance of S–S bond greatly decreases the overpotential compared with S-doping, which results in significant enhancement of the electrocatalytic property. Consequently, the HPCS-S can be an efficient H₂O₂ production electrocatalyst in alkaline solution.