Hydrophobic,Flexible, and Lightweight MXene Foams for High‐Performance Electromagnetic‐Interference Shielding

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.     

On the Characterisation of Foam and Micro‐lattice Materials used in Sandwich Construction1

Abstract: The paper gives an overview of issues relating to the characterisation of the progressive collapse of core cellular materials used in sandwich construction. The specific structural application addressed is foreign object impact, and in this case the core cellular material is subject to multi‐axial stresses, progressive collapse and possible rupture. The paper gives an overview of various theoretical and modelling issues, which are then related to experimental materials and structural tests for model development, calibration and validation. Most discussion concerns polymeric crushable foam, metal foam and metallic lattice structures.     

Engineering 2D Architectures toward High‐Performance Micro‐Supercapacitors

The rise of micro‐supercapacitors is satisfying the demand for power storage in portable devices and wireless gadgets. But the miniaturization of the energy‐storage components is significantly limited by their energy density. Electrode materials with adequate electrochemical active surfaces are therefore required for improving performance. 2D materials with ultralarge specific surface areas offer a broad portfolio of the development of high‐performance micro‐supercapacitors in spite of their several critical drawbacks. An architecture engineering strategy is therefore developed to break these natural limits and maximize the significant advantages of these materials. Based on the approaches of phase transformation, intercalation, surface modification, material hybridization, and hierarchical structuration, 2D architectures with improved conductivity, enlarged specific surface, enhanced redox activity, as well as the unique synergetic effect exhibit great promise in the application of miniaturized supercapacitors with highly enhanced performance. Herein, the architecture engineering of emerging 2D materials beyond graphene toward optimizing the performance of micro‐supercapacitors is discussed, in order to promote the application of 2D architectures in miniaturized energy‐storage devices.     

Ultra‐Light and Scalable Composite Lattice Materials

Architected lattice materials are some of the stiffest and strongest materials at ultra‐light density (<10 mg cm^?3), but scalable manufacturing with high‐performance constituent materials remains a challenge that limits their widespread adoption in load‐bearing applications. We show mesoscale, ultra‐light (5.8 mg cm^?3) fiber‐reinforced polymer composite lattice structures that are reversibly assembled from building blocks manufactured with a best‐practice high‐precision, high‐repeatability, and high‐throughput process: injection molding. Chopped glass fiber‐reinforced polymer (polyetherimide) lattice materials produced with this method display absolute stiffness (8.41 MPa) and strength (19 kPa) typically associated with metallic hollow strut microlattices at similar mass density. Additional benefits such as strain recovery, discrete damage repair with recovery of original stiffness and strength, and ease of modeling are demonstrated.

     

A High‐Performance Lithium‐Ion Capacitor Based on 2D Nanosheet Materials

Lithium‐ion capacitors (LICs) are promising electrical energy storage systems for mid‐to‐large‐scale applications due to the high energy and large power output without sacrificing long cycle stability. However, due to the different energy storage mechanisms between anode and cathode, the energy densities of LICs often degrade noticeably at high power density, because of the sluggish kinetics limitation at the battery‐type anode side. Herein, a high‐performance LIC by well‐defined ZnMn₂O₄‐graphene hybrid nanosheets anode and N‐doped carbon nanosheets cathode is presented. The 2D nanomaterials offer high specific surface areas in favor of a fast ion transport and storage with shortened ion diffusion length, enabling fast charge and discharge. The fabricated LIC delivers a high specific energy of 202.8 Wh kg^?1 at specific power of 180 W kg^?1, and the specific energy remains 98 Wh kg^?1 even when the specific power achieves as high as 21 kW kg^?1.     

Nature‐Inspired Lightweight Cellular Co‐Continuous Composites with Architected Periodic Gyroidal Structures

Shell‐core cellular composites are a unique class of cellular materials, where the base constituent is made of a composite material such that the best distinctive physical and/or mechanical properties of each phase of the composite are employed. In this work, the authors demonstrate the additive manufacturing of a nature inspired cellular three‐dimensional (3D), periodic, co‐continuous, and complex composite materials made of a hard‐shell and soft‐core system. The architecture of these composites is based on the Schoen's single Gyroidal triply periodic minimal surface. Results of mechanical testing show the possibility of having a wide range of mechanical properties by tuning the composition, volume fraction of core, shell thickness, and internal architecture of the cellular composites. Moreover, a change in deformation and failure mechanism is observed when employing a shell‐core composite system, as compared to the pure stiff polymeric standalone cellular material. This shell‐core configuration and Gyroidal topology allowed for accessing toughness values that are not realized by the constituent materials independently, showing the suitability of this cellular composite for mechanical energy absorption applications.

     

Manganese‐Based Na‐Rich Materials Boost Anionic Redox in High‐Performance Layered Cathodes for Sodium‐Ion Batteries

To improve the energy and power density of Na‐ion batteries, an increasing number of researchers have focused their attention on activation of the anionic redox process. Although several materials have been proposed, few studies have focused on the Na‐rich materials compared with Li‐rich materials. A key aspect is sufficient utilization of anionic species. Herein, a comprehensive study of Mn‐based Na_1.2Mn_0.4Ir_0.4O₂ (NMI) O3‐type Na‐rich materials is presented, which involves both cationic and anionic contributions during the redox process. The single‐cation redox step relies on the Mn³⁺/Mn⁴⁺, whereas Ir atoms build a strong covalent bond with O and effectively suppress the O₂ release. In situ Raman, ex situ X‐ray photoelectron spectroscopy, and soft‐X‐ray absorption spectroscopy are employed to unequivocally confirm the reversibility of O₂^2? species formation and suggest a high degree of anionic reaction in this NMI Na‐rich material. In operando X‐ray diffraction study discloses the asymmetric structure evolution between the initial and subsequent cycles, which also explains the effect of the charge compensation mechanism on the electrochemical performance. The research provides a novel insight on Na‐rich materials and a new perspective in materials design towards future applications.     

High‐Performance,Room Temperature,Ultra‐Broadband Photodetectors Based on Air‐Stable PdSe2

Photodetection over a broad spectral range is crucial for optoelectronic applications such as sensing, imaging, and communication. Herein, a high‐performance ultra‐broadband photodetector based on PdSe₂ with unique pentagonal atomic structure is reported. The photodetector responds from visible to mid‐infrared range (up to ≈4.05 µm), and operates stably in ambient and at room temperature. It promises improved applications compared to conventional mid‐infrared photodetectors. The highest responsivity and external quantum efficiency achieved are 708 A W^?1 and 82 700%, respectively, at the wavelength of 1064 nm. Efficient optical absorption beyond 8 µm is observed, indicating that the photodetection range can extend to longer than 4.05 µm. Owing to the low crystalline symmetry of layered PdSe₂, anisotropic properties of the photodetectors are observed. This emerging material shows potential for future infrared optoelectronics and novel devices in which anisotropic properties are desirable.