Ultralight and Highly Resilient Boron Nitride Nanosheet/Polyimide Foams for Energy Harvesting and Sensing

The application of highly superelastic foamlike materials has gradually expanded to various high-end areas, such as filtration purification, mechanical power generation, and energy storage, showing their considerable and expected prospects. In this paper, facile freeze-drying technology combined with a gradual thermal-imidization process was employed to prepare a series of boron nitride nanosheet (BNNS)-filled polyimide (PI) composite foams. These foams can exhibit excellent mechanical properties, including their cyclic stability for considerable cycles under long compressive loading–unloading processes, and their relatively low irreversible deformation. After 10000 cycles at the compression strain of 60%, the total strain loss of the composite filled with 12 wt % is only 14%, which is 2/3 that of pure PI foam. Based on these excellent mechanical characteristics, the foam composites exhibit well a compression-driven triboelectric performance. The effects of BNNS content, compression strain, and rate on the triboelectric properties of the composites were studied in detail. We found that a higher compression strain and compression rate will lead to stronger electrical signals. More significantly, on the basis of the one-to-one relationship between electrical signal and compressive deformation, BNNSs/PI foam will likely be used in the field of control sensing. Finally, the electrical generation device based on composites was used in an insole and keyboard to transform mechanical energy generated by human movement into electrical signals.