Skinless porous films generated by supercritical CO2 foaming for high-performance complementary shaped triboelectric nanogenerators and self-powered sensors

Finding a new, sustainable and scalable approach to fabricate high-performance, durable triboelectric nanogenerators (TENGs) is an ongoing pursuit. In this study, surface-constrained supercritical carbon dioxide (scCO2) foaming was employed to produce skinless porous thermoplastic polyurethane (TPU) film as a novel tribopositive friction material. The skinless porous structure contributed to 340% and 460% enhancement in the output voltage and current, respectively. The performance was further enhanced by over 40% when the concave structured porous TPU film was paired with convex structured polydimethylsiloxane (PDMS) film by constructing a complementary contact state. With an output voltage of 260 V and a current of 46 μA, the optimized TENG achieved a high power density of 4.6 W/m2 on a 3.3 × 106 Ω external load, and displayed the ability to light LEDs, charge capacitors, and power small electronics. The superb flexibility and robustness of TPU and PDMS rendered the flexible TENG excellent stability and durability, as well as the capability to serve as a versatile self-powered sensor that can detect the impact force, various deformations, and monitor human walking behaviours. This work provides an efficient and scalable green approach to produce triboelectric porous films for high-performance TENGs and provides insights into the rational design of friction layers with complementary shapes to boost the energy output.