Rationally designed hierarchical N-doped carbon nanotubes wrapping waxberry-like Ni@C microspheres for efficient microwave absorption

Hierarchical microstructures are playing important roles in the design and fabrication of high-performance microwave absorbing materials (MAMs) owing to their unique advantages. In this work, a series of special “double-hierarchical” N-doped carbon nanotubes wrapping waxberry-like Ni@C microspheres (NC@NCNTs) have been rationally designed and successfully fabricated by two-step pyrolysis processes, where the loading amount of NCNTs on the waxberry-like Ni@C microspheres can be easily modulated by changing the dosage of melamine. Benefiting from sufficient attenuation ability and good impedance matching, NC@NCNTs-2, whose relative carbon content is 51.1 wt%, exhibits the best reflection loss (RL) characteristics among this series of composites, including the minimum RL intensity of −41.5 dB and an effective absorption bandwidth of 5.2 GHz with an absorber thickness of only 1.7 mm. This performance is superior to that of many homologous Ni/C composites reported previously. The investigation on EM properties indicates that the unique “double-hierarchical” architecture of NC@NCNTs can not only create stronger dipole orientation and interfacial polarization relaxation, but can also result in higher conductive loss as well as extra multiple reflection effects for incident electromagnetic waves. We believe that these results will provide some inspirations and pathways for the production of high-performance MAMs with senior microstructures in the future.