Bimetallic nanoarrays embedded in three-dimensional carbon foam as lightweight and efficient microwave absorbers

The rapid development of electronic information technology has promoted the use of a large number of high-frequency electronic equipment, which has led to increasingly serious electromagnetic interference (EMI) problems caused by disordered radiation. At present, for the 2–18 GHz microwave frequency band, it is still a huge challenge to develop high-efficiency absorbing materials with ultra-wide absorption band (>7 GHz) under thin thickness (<3 mm). Here, we propose a new strategy to achieve lightweight and high-efficiency microwave absorption by constructing hierarchical special structures. The melamine foam template was coated with a carbon/nickel/cobalt organic precursor by a hydrothermal process using a water/ethanol mixed solvent, and then annealed in an inert atmosphere at a high temperature to obtain a bimetallic nanoarray composed of nickel/cobalt embedded three-dimensional carbon foam (BNA/3dCF). This new type of absorbing material completely retains the structure of the melamine foam template, greatly enhances the conduction ability of micro-currents, and provides a large number of scattering sites for electromagnetic wave conduction. Interestingly, the protection of the carbon layer effectively avoids the oxidation of the bimetallic nanoarray, so that the BNA/3dCF retains the good dielectric properties of the carbon foam and has excellent magnetic properties, and improves the impedance matching and magnetic loss capabilities. With matching thicknesses of 2.2 mm and 3.9 mm, BNA/3dCF can respectively obtain an ultra-wideband microwave absorption of 7.16 GHz and a minimum reflection loss of −57.84 dB. We believe that through the macro/meso/micro multi-scale precise control of the absorbing material, it is an effective solution to enhance its absorbing performance. • Realize the precise control of the structure on multiple scales. • The bimetallic nanoarray structure was completely preserved. • BNA/3dCF is light enough to be easily held up by a four-leaf clover. • BNA/3dCF-2 achieved an effective bandwidth of 7.16 GHz at 2.2 mm.