Core-shell Ni@C encapsulated by N-doped carbon derived from nickel-organic polymer coordination composites with enhanced microwave absorption

Metal-organic frameworks derived composites have been widely used as absorbers, however, low specific surface area and high filler loading still remain the great challenges for their practical applications. Herein, a coordination assembly strategy is developed for the formation of Ni²⁺-organic polymer coordination composites by the strong chelating ability, then a series of composites composed of core-shell Ni@C encapsulated by N-doped carbon (Ni@C/NC) have been synthesized by a subsequent pyrolysis process. Electromagnetic analysis indicates that increasing the amount of NiCl₂ favors the formation of larger Ni particles, resulting in enhanced conductive and magnetic loss, but leads to decreased dipolar and interfacial polarization. Balancing the above mechanism, for Ni@C/NC-0.5with a specific surface area of 441.2 m² g⁻¹ and 20 wt% filler loading, a minimum reflection loss of −65.1 dB is achieved at 3.5 mm and the effective bandwidth reaches as wide as 8.6 GHz at 2.5 mm, covering the whole Ku band and 65% of X band, the unexceptionable attenuation capacity is attributed to the matched impedance, enhanced dipolar/interfacial polarization as well as multiple scattering. Furthermore, our strategy provides a novel guidance to the development of dielectric-magnetic composites in the application of lightweight and efficient microwave absorbers.