Multi‐Hierarchically Constructing Durable and Flame Retardant CNF/MXene/PDMS Composite Aerogels for Superhigh Electromagnetic Shielding Performance and Ultralow Thermal Conductivity

Abstract There is a significant increase in the demand for lightweight and compressible electromagnetic interference (EMI) shielding materials in various fields. Though MXene aerogels hold immense potential as EMI shielding materials, several shortcomings including poor water resistance, low mechanical robustness, easy oxidation, and high cost limits of their wide application. This work reported a novel strategy involving the co‐assembly of MXene and cellulose nanofibers (CNF) through directional freezing and freeze‐drying, followed by the capsulation‐concreting of a thin layer of flame‐retardant polydimethylsiloxane (PDMS) onto the aerogel, to multi‐hierarchically construct a series of high‐performance CNF/MXene/PDMS composite aerogels. The lightweight CNF/MXene/PDMS/MPP‐Zr@PDA composite aerogel achieved ultrahigh EMI shielding effectiveness of 96.8 dB (X‐band) and utilization efficiency of 1713.27 dB g g −1 . Furthermore, the PDMS coating effectively imparted excellent compressibility and durability to the 3D scaffold, resulting in a compressive strength of 17.01 kPa for the composite aerogel, representing 199.5% increase compared to CNF aerogel. Additionally, the composite aerogel exhibited outstanding flame‐retardant properties (54.6% reduction in heat release rate), ultralow thermal conductivity of 0.0530 W m −1  K −1 and excellent hydrophobicity. Therefore, the durable and flame‐retardant CNF/MXene/PDMS composite aerogels hold promising applications in EMI protection, thermal management, smart fire detection, and other specific fields.