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Abstract M₅X₄MXenes, a subclass of 2D transition metal carbides, have attracted attention as the thickest 2D material synthesized. Early studies show their promising electrocatalytic activity but overlooked how metal composition and interlayer spacing affect hydrogen evolution reaction (HER). To address this gap, three M₅X₄MXenes, Mo₄VC₄, (TiTa)₅C₄, and (TiNb)₅C₄, are systematically studied and their interlayer spacing and composition modulated through ion exchange with tetramethyl ammonium (TMA⁺vs. Li⁺), providing new insights into their HER activity. These findings reveal that TMA⁺‐intercalated Mo₄VC₄exhibits superior HER activity, achieving areal and gravimetric overpotentials of 172 and 90 mV, respectively, due to its composition (presence of Mo) and expanded interlayer spacing that enhances proton accessibility. The Li⁺exchange increases the overpotential to 212 and 131 mV at 10 mA areal and gravimetric current density, respectively, as reduced interlayer spacing restricts access to active Mo sites. In contrast, (TiNb)₅C₄and (TiTa)₅C₄display higher overpotentials, making them more suitable for supercapacitor or aqueous battery applications due to the wider electrochemical window. This study provides critical insights into the interplay between metal composition and interlayer engineering in M₅X₄MXenes, establishing TMA‐Mo₄VC₄as a promising candidate for sustainable hydrogen production. 

Nanoparticles with aerodynamic diameters of less than 100 nm pose serious problems to human health due to their small size and large surface area. Despite continuous progress in materials science to develop air remediation technologies, efficient nanoparticle filtration has appeared to be challenging. This study showcases the great promise of MXene-coated polyester textiles to efficiently filter nanoparticles, achieving a high efficiency of ~90% within the 15–30 nm range. Using alkaline earth metal ions to assist textile coating drastically improves the filter performance by ca. 25%, with the structure–property relationship thoroughly assessed by electron microscopy and X-ray computed tomography. Such techniques confirm metal ions’ crucial role in obtaining fully coated and impregnated textiles, which increases tortuosity and structural features that boost the ultimate filtration efficiency. Our work provides a novel perspective on using MXene textiles for nanoparticle filtration, presenting a viable alternative to produce high-performance air filters for real-world applications. 

Abstract MXenes are a class of 2D materials that have gained significant attention for their potential applications in energy storage, electromagnetic interference shielding, biomedicine, and (opto)electronics. Despite their broad range of applications, a detailed understanding of the internal architecture of MXene‐based materials remains limited due to the lack of effective 3D imaging techniques. This work demonstrates the application of X‐ray micro‐computed tomography (micro‐CT) to investigate various MXene systems, including nanocomposites, coated textiles, and aerogels. Micro‐CT enables high‐resolution, 3D visualization of the internal microstructure, MXene distribution, infiltration patterns, and defect formations, which significantly influence the material's performance. Moreover, the typical technical challenges and limitations encountered during sample preparation, scanning, and post‐processing of micro‐CT data are discussed. The information obtained from optical and electron microscopy is also compared with micro‐CT, highlighting the unique advantages of micro‐CT in providing comprehensive 3D imaging and quantitative data. This study highlights micro‐CT as a powerful and nondestructive imaging tool for characterizing MXene‐based materials, providing insights into material optimization and guidelines for developing future advanced applications. 

The quick progress in communication technologies demands superior electromagnetic interference (EMI) shielding materials. However, achieving a high shielding effectiveness (SE) with thin films, which is needed for microscale, flexible, and wearable devices, through absorption of EM radiation remains a challenge. 2D titanium carbide MXene, Ti3C2Tx, has been shown to efficiently reflect electromagnetic waves. In this paper, we investigated the electromagnetic shielding of ultrathin printed Ti3C2Tx films and recorded absorption up to 50% for 4 nm-thick films. This behavior is explained by impedance matching. Analysis of the sheet impedance in the X-band frequency range allows us to correlate the EMI shielding mechanism with the electrical conductivity measured within the same range. The average bulk in-plane conductivity for 4 to 40 nm-thick films reaches 106 S/m, while the average relaxation time is estimated at around 2.3 ps. Our figures of merit are similar to those reported for ultrathin metal films, such as gold, showing that an abundant MXene material can replace noble metals. We demonstrate that the MXene conductivity mechanism does not change from direct current to THz. The conventional method of reporting EMI SE is correlated with absolute values of transmitted, reflected, and absorbed power, which allows us to interpret previous results on MXene EMI shielding. Considering the easy deposition of thin MXenes films from solution onto a variety of surfaces, our findings offer an attractive alternative for shielding microscale devices and personal electronics. 

Abstract Polyvinylidene fluoride (PVDF) is a semicrystalline polymer used in thin‐film dielectric capacitors because of its inherently high dielectric constant and low loss tangent. Its dielectric constant can be increased by the formation and alignment of its β‐phase crystalline structure, which can be facilitated by 2D nanofillers. 2D carbides and nitrides, MXenes, are promising candidates due to their notable dielectric permittivity and ability to increase interfacial polarization. Still, their mixing is challenging due to weak interfacial interactions and poor dispersibility of MXenes in PVDF. This work explores a novel method for delaminating Ti₃C₂T_xMXene directly into organic solvents while maintaining flake size and quality, as well as the use of a non‐solvent‐induced phase separation method for producing both dense and porous PVDF‐MXene composite films. A deeper understanding of dielectric behavior in these composites is reached by examining MXenes with both mixed and pure chlorine terminations in PVDF matrices. Thin‐film capacitors fabricated from these composites display ultrahigh discharge energy density, exceeding 45 J cm⁻³with 95% efficiency. The PVDF‐MXene composites are also processed using a green and sustainable solvent, propylene carbonate. 

Abstract The origin of MXene's excellent electromagnetic shielding performance is not fully understood. MXene films, despite being inhomogeneous at the nanometer scale, are often treated as if they are compared to bulk conductors. It is reasonable to wonder if the treatment of MXene as a homogeneous material remains valid at very small film thickness and if it depends on the interlayer spacing. The goal of the present work is to test if the homogeneous material model is applicable to nanometer‐thin Ti₃C₂T_xMXene films and, if so, to investigate how the model parameters may depend on variations in MXene interlayer spacings. MXene films containing flakes with interlayer spacing between 1.9 and 5.5 Å have been prepared using various intercalating agents. It is shown that modeling the films as being homogeneous agrees with experimental tests in the microwave frequency range. Microwave conductivity and dielectric constant parameters are estimated for the homogeneous film model by fitting measured results. The direct current (DC) conductivity matches the estimated microwave conductivity on the order of magnitude. A highly effective dielectric constant provides a good fit for the lower conductivity MXene films. Optical absorption agrees with the homogeneous material model of thin films as well.