A facile strategy to achieve necklace like Co/CoO/CNTs nano-composites for enhanced electromagnetic performance

To achieve high electromagnetic microwave absorbing properties, an effective method is to optimize the structural design and composite composition. In this study, we successfully prepared three-dimensional necklace-like composites of Co/CoO/CNTs through solvothermal and hydrogen reduction. The properties were controlled by adjusting the hydrogen reduction time. The results show that the hydrogen reduction time determines the chemical composition (CoO, fcc Co, hcp Co, and CNTs) of the composite material. Specifically, with an increase in hydrogen reduction time, the content of fcc Co and hcp Co increases, with a greater increase in the content of fcc Co compared to hcp Co in cobalt. This subsequently impacts the magnetic properties and electromagnetic parameters of the composite material. As anticipated, the excellent absorbing properties of the composite material are achieved after we use hydrogen reduction for 2 h. At a thickness of 2.69 mm, the RL_min reaches -57.6 dB, with an EABD of 5.4 GHz (12.6–18 GHz) at a thickness of 1.55 mm. Such good performance is inextricably linked to the synergistic effect of the 3D crosslinked conductive network, heterogeneous structure, conduction loss, dielectric loss and magnetic loss in the material, providing multiple loss mechanisms for better impedance matching and reflection loss. The simulated RL results of the composites agree with the experimental values at different thicknesses.