Decorating CoNi Alloy-Encapsulated Carbon Nanotube Hollow Nanocages to Enable Dielectric Loss for Highly Efficient Microwave Absorption

Metal–organic framework-derived carbon materials have attracted considerable attention as efficient electromagnetic microwave absorption (EMA) materials due to their tunable structure and components. However, their poor electrical conductivity and restricted pore volume lead to poor impedance matching and high filler content, limiting further applications. Herein, an efficient strategy is proposed for designing hollow CoNi/carbon nanotube (CNT)/hollow carbon nanocage (HCN) composites through Ni2+ etching and subsequent thermal catalysis treatment. The CoNi alloy nanoparticle-encapsulated CNTs are decorated on the surface of HCNs and unique CoNi alloy nanoparticles on the top of the CNT. The introduction of CNTs not only enhances the attenuation capacity of the electromagnetic microwave (EMW) but also effectively maintains the hollow structure of the matrix to optimize impedance matching characteristics and construct abundant heterogeneous interfaces with the CoNi alloy, enhancing the interfacial polarization loss. Benefitting from the hollow structure and a large number of micropores which facilitate impedance matching, the strong conduction loss, and enhanced interfacial polarization loss of the CNT, the dielectric loss of CoNi/CNT/HCNs is effectively improved. CoNi/CNT/HCNs exhibit excellent EMA performance with a minimum reflection loss of −59.5 dB and achieve a maximum effective absorption bandwidth of 7.1 GHz at 1.8 mm. This study not only proposes an effective strategy to achieve an efficient EMW absorber with a strong attenuation and broadband but also provides insights into how to maintain the hollow structure of the substrate.