MXene/Ag@ZnO/WPU/Melamine gradient composite foams prepared by a unidirectional evaporation approach for absorption-dominated electromagnetic interference shielding

Gradient electromagnetic interference (EMI) shielding materials with absorption-dominated characteristics are promising but always have problems like complicated steps or harsh operation conditions. Herein, we propose a gradient EMI composite foam of MXene/Ag@ZnO/WPU/Melamine fabricated through a simple unidirectional evaporation in combination with a vacuum-drying method. Benefiting from it, the conductivity of the material decreases from the top and bottom to the middle. The top with good impedance matching, which allows electromagnetic waves to enter the material, and the bottom with an efficient conductive network, which ensures an excellent EMI SE of the composite foam, could be balanced owing to the difference in the dispersibility of MXene and Ag@ZnO. Under the effect of "absorb-reflect-reabsorb", the as-prepared M2A3F composite material exhibits a high EMI SE of 39.90 dB and a low reflectivity coefficient of 0.1423 with an ultra-low volume ratio (2.72 % MXene and 4.25 % Ag). In addition, it features good mechanical properties, especially cyclic compression recovery. In sum, this study provides a novel solution for preparing high-performance EMI materials with absorption-dominated characteristics on a large scale.