Ultra-Broadband Microwave Absorbers via Gradient EM Parameters and Engineered Nanogaps in 1D NiO/Ni/Gap/C Composites

Rational design of carbon fiber (CF)-based dielectric-magnetic-electric ternary composites offers a promising pathway to reconcile impedance matching with enhanced attenuation capacity. However, achieving ultrawide effective absorption bandwidths while elucidating the intricate electromagnetic energy dissipation mechanisms remains a persistent challenge. In this work, we report a hierarchical one-dimensional NiO/Ni/Gap/carbon (NNGC) synthesized through electroplating-assisted anchoring of nickel nanoparticles and reduced graphene oxide (rGO) on carbon fibers, followed by high-temperature redox engineering. The optimized architecture features porous NiO outer shells, Ni inner shells, a thin gap between shell and CF, gradient electromagnetic parameters (EM), and a continuous conductive carbon network, synergistically enabling exceptional impedance matching and intensified conductive losses. Interface engineering across NiO, metallic Ni, and graphene–carbon fiber heterojunctions induces pronounced interfacial polarization, as systematically validated through theoretical calculations. The synergy of structural and compositional optimization yields an excellent microwave absorption performance: for NNGC-4.5, a remarkable RL min of −49.85 dB (13.9 GHz) is attained at 2.0 mm. And the NNGC-10.5 with a 0.74 μm porous NiO outer layer and 0.28 μm Ni inner layer achieves an ultrawide effective absorption bandwidth (EAB) of 12.2 GHz (5.8–18.0 GHz) while maintaining a thickness of 4.0 mm. This work pioneers a gradient strategy in multilayered one-dimensional (1D) architectures, establishing a universal paradigm for developing microwave absorbers that simultaneously satisfy stringent requirements of a thin profile, lightweight design, broadband operation, and high attenuation efficiency.