Hierarchical Multi-Core-Shell CoNi@Graphite Carbon@Carbon Nanoboxes for Highly Efficient Broadband Microwave Absorption

The rational construction of a core-shell structure has been widely used in the design of absorbing materials for improved impedance and attenuation matching. However, for traditional absorbing core-shell materials, it is crucial to further regulate the morphology and composition of the core after encapsulation, to realize further improvement in absorbing performance. In this work, heterogeneous multi-core-shell CoNi@graphite carbon@carbon (hereinafter referred to as CGC) nanocomposites have been fabricated via the polymerization of dopamine on the surface of cobalt-nickel Prussian blue analogues and subsequent carbonization. Because of the effect of metal catalytic graphitization, the CoNi alloy formed during high-temperature carbonization promotes the transitional process from amorphous carbon to graphite, thus forming a multi-core-shell structure with the CoNi alloy coated with graphite carbon as the core and amorphous carbon as the shell. Notably, the as-prepared CGC nanocomposites with an optimized paraffin loading ratio exhibit superior electromagnetic wave (EMW) absorbing capacity, reaching a minimum reflection loss value of -56.78 dB at 14.76 GHz with a thickness of 2.0 mm, much better than that of most magnetic carbon-based absorbing materials as reported previously. Furthermore, the effective bandwidth goes across 5.51 dB (12.34-17.85 GHz), therefore enriching the absorbing application in the Ku band. As a result, the superior impedance and attenuation matching derived from the heterogeneous multi-core-shell structure and multiple electromagnetic loss components make CGC a promising EMW absorbing material.