Sijia Liu, Chun‐Shuai Cao, Dan Liú, Shiguang Pan, Aijing Ma, Jianzhou Gui
Rapid advancements in integrated multifunctional electronics have intensified the demand for high-performance composite phase change materials (PCMs) that combine thermal management, solar–thermal conversion, and microwave absorption. In this study, a hierarchical porous Fe–N–C carrier was prepared via a green two-step approach using biomass-derived tannic acid etching, followed by controlled carbonization. n -Docosane ( n -22) was dual-encapsulated by Fe–N–C and an additional silica shell for effective PCM composite n -22@Fe–N–C@SiO 2 . The resulting material exhibits a high latent heat of 130.7 J/g with minimal permeability (4.31%), an outstanding solar–thermal conversion efficiency of 89.18%, and superior microwave absorption performance, achieving a minimum reflection loss of −35.10 dB at 5.45 GHz and an ultrawide absorption bandwidth of 7.16 GHz, effectively covering the entire X band. The graphitized carbon framework and uniformly dispersed Fe 3 O 4 nanoparticles synergistically reduce interfacial thermal resistance, enhance photon capture and phonon transport, and notably increase the conductivity loss and magnetic loss for microwave absorption, endowing n -22@Fe–N–C@SiO 2 as a promising candidate for integrated thermal management and electromagnetic protection for both electronics and wearable radiation-proof textiles.