A hierarchically structured g-C3N4/FeCo@CNT composite for synergistic corrosion resistance and microwave absorption at elevated temperature

A hierarchical g-C 3 N 4 /FeCo@CNT composite is fabricated by a three-stage strategy. • CNT shells protect FeCo cores from thermal oxidation and electrochemical corrosion. • At 400 °C, RLmin reaches −22.01 dB with 4.03 GHz EAB, showing thermal resilience. • This work unites broadband absorption, thermal stability, and corrosion resistance. Graphitic carbon nitride (g-C 3 N 4 ) is emerging as a promising microwave absorbing material owing to its chemical/thermal stability and tunable dielectric properties. However, its intrinsic low electrical conductivity and the lack of magnetic loss mechanism present obstacles to practical applications. Herein, a hierarchically structured g-C 3 N 4 /FeCo@CNT composite was fabricated via a three-stage sequential strategy. The hollow tubular g-C 3 N 4 framework serves as a low-density dielectric scaffold and facilitates multiple internal reflections, whereas the FeCo@CNT hybrids establish a conductive network and contribute substantial magnetic loss. Moreover, the CNT shell effectively protects the FeCo cores against thermal oxidation and electrochemical corrosion. Benefiting from the balanced dielectric–magnetic synergy, the composite achieves an effective absorption bandwidth (EAB) of 4.07 GHz at a thickness of only 2.2 mm, with a minimum reflection loss ( RL min ) of −17.86 dB at room temperature. Notably, the RL min further reaches −22.01 dB and the corresponding bandwidth remains 4.03 GHz at 400 °C, underscoring exceptional high-temperature resilience. This research offers new insights into the rational design of g-C₃N₄-based microwave absorbers that simultaneously reconcile broadband microwave absorption with high-temperature stability and corrosion resistance.