Constructing core-shell structural bimetallic CoNi alloys doped carbon aerogels for highly efficient electromagnetic wave absorption

Magnetic metallic particles (Fe, Co, Ni) doped phenolic-aldehyde-based carbon aerogels (CAs) have been widely used in the realms of electromagnetic wave absorption (EMA). However, the effect of molar ratios of Co and Ni on their properties have not been revealed in detail, and their EMA performance still need to be improved. In this study, by using resorcinol and formaldehyde as precursors, core-shell structural bimetallic cobalt (Co)-nickel (Ni) alloys doped CAs (CoNi-CAs) were firstly prepared by a facile method, leading to the enhance of EMA performance. The effect of molar ratios of Co and Ni on the composition, microstructure, porous structure, EMA performance and radar-cross-section (RCS) values of CoNi-CAs were firstly investigated in detail. The results reveal the prepared CoNi-CAs are porous core-shell structural materials and possess excellent EMA performance both in the low and high frequency range. In the X-band (8–12 GHz) and K_u-band (12–18 GHz), the maximum effective-absorption-bandwidth (EAB_max) is located at CoNi-CAs (S-5) and reaches 5.7 GHz (only 1.76 mm) while its minimum reflection-loss (RL_min) achieves −40.69 dB (at 2.41 mm). Meanwhile, in the C-band (4–8 GHz), the CoNi-CAs (S-5) display an EAB_max of 2.5 GHz. Moreover, the minimum RCS value of CoNi-CAs (S-3) reaches −43.68 dB m² over a range of 0° to 360°. The excellent EMA performance of CoNi-CAs can be ascribed to the conduction loss derived from graphitized carbon, the polarization loss resulted from the core-shell structure, the good magnetic loss of CoNi alloys, and the improved impedance matching characteristics due to the synergistic effect of dielectric loss and magnetic loss at a specific Co/Ni molar ratio. Furthermore, this straightforward approach offers a pathway for creating other metal-doped CAs in a cost-effective and uncomplicated manner.