Self-Templating Engineering of Hollow N-Doped Carbon Microspheres Anchored with Ternary FeCoNi Alloys for Low-Frequency Microwave Absorption

Rational design and precision fabrication of magnetic-dielectric composites have significant application potential for microwave absorption in the low-frequency range of 2–8 GHz. However, the composition and structure engineering of these composites in regulating their magnetic-dielectric balance to achieve high-performance low-frequency microwave absorption remains challenging. Herein, a self-templating engineering strategy is proposed to fabricate hollow N-doped carbon microspheres anchored with ternary FeCoNi alloys. The high-temperature pyrolysis of FeCoNi alloy precursors creates core-shell FeCoNi alloy-graphitic carbon nano-units that are confined in carbon shells. Moreover, the anchored FeCoNi alloys play a critical role in maintaining hollow structural stability. In conjunction with the additional contribution of multiple heterogeneous interfaces, graphitization, and N doping to the regulation of electromagnetic parameters, hollow FeCoNi@NCMs exhibit a minimum reflection loss (RL_min) of −53.5 dB and an effective absorption bandwidth (EAB) of 2.48 GHz in the low-frequency range of 2–8 GHz. Furthermore, a filler loading of 20 wt% can also be used to achieve a broader EAB of 5.34 GHz with a matching thickness of 1.7 mm. In brief, this work opens up new avenues for the self-templating engineering of magnetic-dielectric composites for low-frequency microwave absorption.