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.