From MXene Trash to Ultraflexible Composites for Multifunctional Electromagnetic Interference Shielding

GO-Enhanced MXene Sediment-Based Inks Achieve Remarkable Oxidation Resistance and High Conductivity

MXenes are emerging materials renowned for their exceptional conductivity, abundant functional groups, and excellent solution processability, making them highly promising as conductive-additive-free inks for flexible electronic devices. However, current preparation methods are hampered by low yields of MXene flakes so that substantial waste MXene sediments (MS) are generated. Here, we demonstrate a type of conductive ink with appropriate rheological properties, namely MG inks formulated using MS and graphene oxide (GO), for screen-printing frequency selective surface (FSS). GO facilitates interlayer interactions by covalently cross-linking with MXene flakes, resulting in a denser structure and significantly enhancing the conductivity of the best-performing MG-based ink to 849 S cm-1. Additionally, GO serves as a binder to considerably improve the rheological properties of MS, thus enabling high-quality printing on various substrates. The close stacking of MS and GO not only improves the oxidation resistance but also maintains conductivity above 97% even after 60 days. Furthermore, the MG-based FSS produced via straightforward screen printing demonstrates excellent performance and retains its functionality after 90 days of operation. This MS-based ink formulation represents a strategy of "turning trash into treasure" and highlights the potential of MS for the next generation of electronic devices.

Controlled Distribution of MXene on the Pore Walls of Polyarylene Ether Nitrile Porous Films for Absorption-Dominated Electromagnetic Interference Shielding Materials

With the increasing application of electronic devices, absorption-dominated electromagnetic interference shielding materials (EMISM) have garnered significant attention for preventing secondary electromagnetic pollution. In this study, polyethyleneimine (PEI)-modified MXene (PEI@MXene) is fabricated and achieved its controlled distribution on the pore walls of polyarylene ether nitrile (PEN) porous films via the phase inversion method (PIM) to obtain a closed porous skeleton of MXene on the pore walls (CPS-MPW). The resulting PEI@MXene/PEN composite film (CFx) exhibited absorption-dominated EMIS efficiency (EMISE). Attributing to the strong interaction between PEI and the hydrophilic segment of amphiphilic Pluronic F127, with its hydrophobic segment anchored by the PEN matrix, PEI@MXene is directionally distributed on the pore walls of CFx. In addition, resulting from the cladding of MXene with PEI and isolating it with closed honeycomb pores, the obtained CFx are insulators without forming a conductive network. As a result, these CFx demonstrate absorption-dominated EMISE with the highest SET of 41.2 dB and coefficient A higher than 0.51. Further continuous hot pressing of CFx results in thinner and denser films with an impressive specific EMISE up to 750 dB cm-1. The successful fabrication of these CPS-MPW-type CFx with absorption-dominated EMISE provides a reference for developing and preparing novel EMISM.

Recent Advances in MXene-Based Aerogels for Electromagnetic Wave Absorption

Developing lightweight, high-performance electromagnetic wave (EMW) absorbing materials those can absorb the adverse electromagnetic radiation or waves are of great significance. Transition metal carbides and/or nitrides (MXenes) are a novel type of 2D nanosheets associated with a large aspect ratio, abundant polar functional groups, adjustable conductivity, and remarkable mechanical properties. This contributes to the high-efficiency assembly of MXene-based aerogels possessing the ultra-low density, large specific surface area, tunable conductivity, and unique 3D porous microstructure, which is beneficial for promoting the EMW absorption. Therefore, MXene-based aerogels for EMW absorption have attracted widespread attention. This review provides an overview of the research progress on MXene-based aerogels for EMW absorption, focusing on the recent advances in component and structure design strategies, and summarizes the main strategies for constructing EMW absorbing MXene-based aerogels. In addition, based on EMW absorption mechanisms and structure regulation strategies, the preparation methods and properties of MXene-based aerogels with varieties of components and pore structures are detailed to advance understanding the relationships of composition-structure-performance. Furthermore, the future development and challenges faced by MXene-based aerogels for EMW absorption are summarized and prospected.

Electromagnetic Interference Shielding and Joule Heating Properties of Flexible, Lightweight, and Hydrophobic MXene/Nickel-Coated Polyester Fabrics Manufactured by Dip-Dry Coating and Electroless Plating

High-performance electromagnetic interference (EMI) shielding materials with high flexibility, low density, and hydrophobic surface are crucial for modern integrated electronics and telecommunication systems in advanced industries like aerospace, military, artificial intelligence, and wearable electronics. In this study, we present flexible and hydrophobic MXene/Ni-coated polyester (PET) fabrics featuring a double-layered structure, fabricated via a facile and scalable dip-dry coating process followed by electroless nickel plating. Increasing the dip-dry coating iterations up to 10 cycles boosts the MXene loading content (∼31 wt %) and electrical conductivity (∼86 S/cm) of MXene-coated PET fabrics, while maintaining constant porosity (∼95%). The addition of a Ni layer enhances hydrophobicity, achieving a high water contact angle of ∼114° compared to only MXene-coated PET fabrics (∼49°). Furthermore, the 30 μm thick MXene/Ni-coated PET fabric demonstrates superior electrical conductivity (∼113.8 S/cm) and EMI shielding effectiveness (∼35.7 dB at 8-12 GHz) compared to only MXene- or Ni-coated PET fabrics. The EMI shielding performance of the MXene/Ni-coated PET fabric remains more stable in an air environment than only MXene-coated fabrics due to the outer Ni layer with excellent hydrophobicity and oxidation stability. Additionally, the MXene/Ni-coated PET fabric exhibits impressive Joule heating performance, swiftly converting electrical energy into heat and reaching high steady-state temperatures (32-92 °C) at low applied voltages (0.5-1.5 V).

Structural Design for EMI Shielding: From Underlying Mechanisms to Common Pitfalls

Modern human civilization deeply relies on the rapid advancement of cutting-edge electronic systems that have revolutionized communication, education, aviation, and entertainment. However, the electromagnetic interference (EMI) generated by digital systems poses a significant threat to the society, potentially leading to a future crisis. While numerous efforts are made to develop nanotechnological shielding systems to mitigate the detrimental effects of EMI, there is limited focus on creating absorption-dominant shielding solutions. Achieving absorption-dominant EMI shields requires careful structural design engineering, starting from the smallest components and considering the most effective electromagnetic wave attenuating factors. This review offers a comprehensive overview of shielding structures, emphasizing the critical elements of absorption-dominant shielding design, shielding mechanisms, limitations of both traditional and nanotechnological EMI shields, and common misconceptions about the foundational principles of EMI shielding science. This systematic review serves as a scientific guide for designing shielding structures that prioritize absorption, highlighting an often-overlooked aspect of shielding science.

An Asymmetric Layer Structure Enables Robust Multifunctional Wearable Bacterial Cellulose Composite Film with Excellent Electrothermal/Photothermal and EMI Shielding Performance

Highly robust flexible multifunctional film with excellent electromagnetic interference shielding and electrothermal/photothermal characteristics are highly desirable for aerospace, military, and wearable devices. Herein, an asymmetric gradient multilayer structured bacterial cellulose@Fe3O4/carbon nanotube/Ti3C2Tx (BC@Fe3O4/CNT/Ti3C2Tx) multifunctional composite film is fabricated with simultaneously demonstrating fast Joule response, excellent EMI shielding effectiveness (EMI SE) and photothermal conversion properties. The asymmetric gradient 6-layer composite film with 40% of Ti3C2Tx possesses excellent mechanical performance with exceptional tensile strength (76.1 MPa), large strain (14.7%), and good flexibility. This is attributed to the asymmetric gradient multilayer structure designed based on the hydrogen bonding self-assembly strategy between Ti3C2Tx and BC. It achieved an EMI SE of up to 71.3 dB, which is attributed to the gradient "absorption-reflection-reabsorption" mechanism. Furthermore, this composite film also exhibits excellent low-voltage-driven Joule heating (up to 80.3 °C at 2.5 V within 15 s) and fast-response photothermal performance (up to 101.5 °C at 1.0 W cm-2 within 10 s), which is attributed to the synergistic effect of heterostructure. This work demonstrates the fabrication of multifunctional bacterial cellulose@Fe3O4/carbon nanotube/Ti3C2Tx composite film has promising potentials for next-generation wearable electronic devices in energy conversion, aerospace, and artificial intelligence.

Structure Design and Processing Strategies of MXene-Based Materials for Electromagnetic Interference Shielding

The development of new materials for electromagnetic interference (EMI) shielding is an important area of research, as it allows for the creation of more effective and high-efficient shielding solutions. In this sense, MXenes, a class of 2D transition metal carbides and nitrides have exhibited promising performances as EMI shielding materials. Electric conductivity, low density, and flexibility are some of the properties given by MXene materials, which make them very attractive in the field. Different processing techniques have been employed to produce MXene-based materials with EMI shielding properties. This review summarizes processes and the role of key parameters like the content of fillers and thickness in the desired EMI shielding performance. It also discusses the determination of power coefficients in defining the EMI shielding mechanism and the concept of green shielding materials, as well as their influence on the real application of a produced material. The review concludes with a summary of current challenges and prospects in the production of MXene materials as EMI shields.