A dynamic supercritical carbon dioxide foaming method for fabricating wrinkled surface to enhance triboelectric nanogenerator performance

Triboelectric nanogenerator (TENG) is a promising energy harvester to overcome the energy depletion issue. The surface structure has been considered as an effective way to enhance the triboelectric performance. Herein, a dynamic supercritical carbon dioxide (scCO2) foaming method, which introduced a scCO2 flow field during scCO2 saturation, was proposed to fabricate thermoplastic polyurethane (TPU) foams with surface wrinkly structures. The size of the surface wrinkles could be regulated in the range of 1.8–10 μm by varying the foaming pressure. The surface wrinkled TPU film with wrinkle wave length of 2.4 μm demonstrated an excellent enhancement in output voltage (130%), current (180%), and maximum transfer charge (130%) when paired with surface structured polydimethylsiloxane film in a TENG. Due to the excellent durability and flexibility of the composing materials, the developed TENG showed outstanding stability in long‐term continuous operation. With a high power density of 0.5 W/m2 achieved on a 107 Ω external load, the flexible TENG could be used to charge capacitors, power light‐emitting‐diodes, and served as a self‐powered sensor to detect various human movement behaviors. This work provides a new path for the fabrication of surface wrinkled films for the sustainable development of high performance TENGs. Surface wrinkled thermoplastic polyurethane (TPU) films were prepared by dynamic supercritical carbon dioxide (scCO2) foaming by applying a scCO2 flow field to the material during the soaking process. The triboelectric nanogenerator (TENG) developed based on the wrinkled TPU film achieved dramatic triboelectric output performance enhancement due to the increased roughness and surface area. Attributing to the durability of TPU, the TENG demonstrated high stability, charging performance, and ability to detect motion state of human.