Hybrid bilayers of carbon/NiBr₂ anchoring on FeSiB surface for enhanced microwave absorption coupling with smart discoloration

Developing bifunctional materials with smart discoloration and microwave absorption properties has attracted widespread interest in microwave absorption/shielding, yet it is challenging for reversible discoloration performance in humid (such as forest) and dry (desert) environments. Herein, we combined catalytic chemical vapor deposition (CCVD) technology and a hydrothermal synthesis method to develop a FeSiB@C@NiBr₂ atomic-scale double-shell gradient structure with rich interfaces. These nanosheet arrays favor interface polarization, impedance matching, and dipole polarization of the material, thereby optimizing the microwave absorption performance. The optimal reflection loss (RL) value of FeSiB@C@NiBr₂ reached − 59.6 dB at 9.2 GHz, and the effective absorption bandwidth (EAB) reached 7.0 GHz at a thickness of 2.5 mm. Compared with pure FeSiB (RL_min of − 13.5 dB), the RL_min value of the absorber designed by this method increased by ~ 3 times. The color of NiBr₂ in the outermost nanosheet arrays changes between yellow and green in the case of water molecule harvesting and loss, respectively. This novel FeSiB@C@NiBr₂ composite structure material is expected to provide a promising platform for wave-absorbing and smart discoloring materials.