Rational design of yolk-shell NiCo2O4@void@NiCo2S4 nanospheres for effective enhancement in microwave absorption

An efficient strategy for the synthesis of rational designed yolk-shell nanospheres with NiCo2O4 core and NiCo2S4 shell has been developed in this work. Firstly, NiCo2O4 solid nanospheres are synthesized as precursors, and then the yolk-shell NiCo2O4@void@NiCo2S4 nanospheres are obtained by further controllable sulfidation process. Combing the dielectric losses arising from the dielectric materials of NiCo2O4, NiCo2S4 and the extraordinary polarization losses generating between the core and shell in rational designed yolk shell structure, the optimized NiCo2O4@void@NiCo2S4 composite samples by exactly controlling the sulfidation time can exhibit the superior microwave absorption properties. It is worth noting that the optimal Refection Loss (RL) value of NiCo2O4@void@NiCo2S4 composites could achieve -58.5 dB at 7.76 GHz with a thickness of 2.8 mm and the absorption bandwidth for RL < -10 dB could range from 11.6 GHz to 18 GHz (6.4 GHz) with a thickness of 1.9 mm. The as-synthesized NiCo2O4@void@NiCo2S4 composite with proper sulfidation time could be a promising microwave attenuation material with strong dielectric loss capability and wide absorbing bandwidth. (C) 2020 Elsevier B.V. All rights reserved.