High‐Entropy Interface Engineering in Multifunctional Green Fiber Aerogels for Coupled Electromagnetic and Waste‐Heat Management

Abstract Electromagnetic wave absorption (EMWA) and waste‐heat management are vital for sustainable electronic and energy systems. However, most research focuses on enhancing EMWA while neglecting heat dissipation, which makes it difficult to design materials with both broadband absorption and multifunctional stability. To overcome this challenge, high‐entropy effects are introduced into green flexible biomass‐derived fiber aerogels, thereby combining sustainability with advanced electromagnetic performance. In this work, ultrathin high‐entropy layered hydroxide (HEL) nanosheets are uniformly anchored on natural fiber substrates to construct high‐entropy interfaces for the synergistic regulation of electromagnetic and thermoelectric loss mechanisms. The high‐entropy effect induces electronic redistribution, while elemental heterogeneity generates localized polarization and facilitates lateral electron migration, enhancing dielectric loss and EMWA performance. Simultaneously, lattice‐induced strain increases interfacial density and strengthens coupling, suppressing thermal conductivity and improving the Seebeck effect. X‐ray absorption fine structure (XAS) analysis and density functional theory (DFT) calculations further validate this interfacial regulation mechanism. Benefiting from these synergistic effects, the fabricated devices exhibit outstanding EMWA efficiency, effective thermal management, and excellent infrared stealth. This study demonstrates the advantages of high‐entropy‐enabled green multifunctional fiber‐assembled aerogels, offering a flexible strategy for the design of next‐generation EMWA and sustainable energy conversion materials.