Anti-oxidation polyimide-based hybrid foams assembled with bilayer coatings for efficient electromagnetic interference shielding

High-performance electromagnetic interference (EMI) shielding materials are highly desirable in high-tech fields, particularly in high temperature conditions, whereas long term effectiveness of the EMI shielding performance still remains a challenge. Herein, polyimide-based PI@MXene@ANFs/PI hybrid foams assembled with MXene and polyimide bilayer coatings were fabricated via a facile strategy of freeze-drying plus thermal imidization followed by two-step dip-coating. More specifically, MXene coating acted as conducting layer to ensure the electrical conductivity of hybrid foams and polyimide coating served as protecting layer to enhance the long-term effectiveness of the hybrid foams by protecting MXene coating from oxidation during use. Benefiting from the conductive MXene coating and porous structure of the as-prepared hybrid foams, massive EMWs were converted into heat energy via ohmic losses, resulting in excellent EMI shielding performance of MXene@ANFs/PI and PI@MXene@ANFs/PI hybrid foams with an absorption-dominant EMI shielding mechanism in terms of EMI SE. After heat-treated at 250 °C for 100 h, the average EMI SET of PI@MXene@ANFs/PI-35 foam was slightly decreased by 4.97% from 46.3 to 44.0 dB, yet 65.85% from 48.9 to 16.7 dB for MXene@ANFs/PI-35 foam. The results indicated that the special bilayer coatings endowed the polyimide-based foams with lightweight, outstanding EMI shielding and anti-oxidation performance, presenting great prospects for the long-term application in extreme conditions.