Macro-ordered porous carbon nanocomposites for efficient microwave absorption

Tunable and efficient porous carbon-based microwave absorbers are essential in electromagnetic compatibility and protection due to their pronounced dielectric losses and ultralow density. However, it is still challenging to achieve satisfactory impedance matching and attenuation ability owing to the difficulty of realizing custom-designed porous structures. Herein, we propose a material-structure collaborative approach which includes multi-scaling, component modulation and systematic investigation of macroscopic structures. Macro-ordered porous carbon nanocomposites (MOPCN) assembled with MWCNTs and chitosan (CHI) were fabricated via freeze casting and MWCNTs/CHI ratio regulation. By simply varying the freezing temperature gradient distri-bution from radial (R) to axial (A), radial-centrosymmetric and honeycomb-like pore arrays were realized respectively. Compared with the honeycomb-like pore array, the radial-centrosymmetric pore array imparts much stronger microwave attenuation capability due to enhanced phase contiguity and optimized spatial arrangement. Such configuration also enabled one to optimize impedance matching and absorption, alleviating the over-dependence of microwave absorption performance on material composition. Optimum absorption of up to -70.6 dB at 9.3 GHz and -72.9 dB at 8.8 GHz were achieved for the MOPCN-1/4-R and MOPCN-1/2-A composites, respectively, with effective absorption band covering the entire X-band at a low filler loading of 1 wt%. Overall, this study provides a further understanding of the structure-property relationship and paves the way for future exploration of plainified microwave absorbers based on optimized macropore structures while preserving low filler loading.