Rational design of two-dimensional flaky Fe/void/C composites for enhanced microwave absorption properties.

Owing to their unique electromagnetic properties and structure anisotropy, two-dimensional (2D) magnetic metal flakes are attracting special attention for applications as microwave absorption materials. However, the conductive network formed by the connected metal flakes may lead to impedance mismatching and reduced performance. In this study, a facile and rational strategy was developed to fabricate yolk-shell-structured 2D flaky Fe/void/C composites by using α-FeO hexagonal flakes as the template, followed by the coating of polydopamine (PDA) on the composite surface and calcination under H/Ar. The volume shrinkage from FeO to Fe and PDA to carbon led to the formation of several irregular holes in Fe flakes and void space between the Fe cores and carbon cages. The thickness of carbon cages of the composites can be tailored by the simple modulation of the synthetic parameters. As a result of the synergistic effects of multiple chemical components, the shape anisotropy of iron flakes, and unique yolk-shell structures, the optimized sample exhibited excellent microwave absorption properties. With a matching thickness of only 1.6 mm, the strongest reflection loss (RL) was up to -27.80 dB at 14.72 GHz, and the effective absorption bandwidth (EAB, RL < -10 dB) reached 6.40 GHz (11.60-18.00 GHz), which can cover the whole Ku-band. This study provides a novel approach to adjust and balance the permeability and permittivity of 2D magnetic metal flakes, which may promote the practical applications of flaky magnetic metal materials in microwave absorption.