Magnetic Ni/graphene connected with conductive carbon nano-onions or nanotubes by atomic layer deposition for lightweight and low-frequency microwave absorption

Microwave absorbing materials (MAMs) have been researched in depth due to the increasing electromagnetic (EA) pollution produced by rapid-developed electronic technologies. Lightweight and high-conductivity graphene-based MAMs are quite promising, but there also exists a big challenge for them to achieve satisfactory low-frequency microwave absorption performance with a low filler loading ratio. Here, two novel hierarchical structures, Ni@carbon nano-onions and Ni/carbon nanotubes adhering on graphene surfaces (Ni@C/G and Ni/CNT/G) were designed and synthesized by precisely controlling the size and content of NiO with an atomic layer deposition-assisted method. Such innovative constructions can endow them a variety of advantages for microwave absorption including multiple interfaces, micro-current networks and good impedance matching, which ensures them to be high-efficiency and low-frequency microwave absorbers with low densities. Optimized NCG 100 exhibits excellent microwave absorption performance in C band with the minimum RL value reaching -45.5 dB at 6.2 GHz, and the widest absorption band was measured to be 5.6 GHz at the thickness of 2.5 mm. In addition, compared to most of graphene- and Ni-based absorbers, Ni@C/G and Ni/CNT/G achieve higher performance by utilizing a lower filler loading ratio of only 15%. Our findings may pave the way for designing lightweight low-frequency MAMs.