1D CNT-Expanded 3D Carbon Foam/Si₃N₄ Sandwich Heterostructure: Utilizing the Polarization Compensation Effect for Keeping Stable Electromagnetic Absorption Performance at Elevated Temperature

Modern electromagnetic (EM) absorbing materials (EAMs) are experiencing a revolution triggered by advanced information technology. Simultaneously, the diverse harsh EM application scenarios entail a more stringent appeal of practicability to EAMs, especially under high-temperature conditions. Therefore, exploring EAMs with both excellent absorbing performance and practicability at elevated temperatures is necessary. Herein, a novel 3D porous carbon foam/carbon nanotubes@Si3N4 (CF/CNTs@Si3N4) heterostructure was constructed by the chemical vapor infiltration process. The optimally grown 1D CNTs embedded in 3D CF/Si3N4 are utilized to provide abundant nanointerface coupling effects to compensate for the excessive increase in the conductive loss during rising temperature to realize a self-adjustment in response to high temperature. A high-efficiency EM absorption over a wide temperature range from 25 to 480 °C was achieved (with a ≥90% absorbing ratio covering the whole X-band). In addition, the Si3N4 coating can improve the thermal stability of the carbon matrix and maintain the tailored inner structure. Multiple investigations into other environmental adaptabilities also exhibited the application perspective of such a heterostructure. This work points out a new strategy for preparing designable, efficient, and high-temperature applicable EAMs, promoting the diverse development of electronic devices.