Integrated and shape-adaptable multifunctional flexible triboelectric nanogenerators using coaxial direct ink writing 3D printing

Triboelectric nanogenerators (TENGs), particularly those with high flexibility and sophisticated geometry, have shown great application foreground in portable and wearable electronics. However, traditional fabrication approaches remain complicated and non-versatile, which are also impractical in the preparation of complex shapes and structures. Herein, a one-pot coaxial direct ink writing (DIW) 3D printing technique has been proposed to fabricate a fully flexible single-electrode TENG (FFTENG) with sophisticated shapes and 3D structures for the purpose of harvesting and utilizing biomechanical energy. This FFTENG is made up of a silicone elastomer shell as the triboelectric layer and an inner silicone/carbon black (CB) core as the flexible electrode. Various factors that affect the output electric performance, including the ratio of the inner and outer diameter of the printed fiber, CB content, loading frequency, applied contact force, specimen size, and external load resistance, are investigated in detail via the contact-separation test. The results show that a standard square FFTENG with a size of 30 × 30 mm2 can yield an open-circuit voltage (Voc), a short-circuit current (Isc) and a short-circuit transferred charge (Qsc) of as high as 60 V, 0.23 μA and 58 nC, respectively, and a maximum output peak power density of 15.59 mW m−2 at a matched resistance of 80 MΩ. More importantly, various shape-adaptable FFTENGs can be designed and tailored to meet the diverse needs of different applications, such as self-powered LED systems, self-charging power systems, LED control devices, self-powered tactile sensors, flexible self-monitoring grip exercisers, and flexible self-powered keyboards, and open up new avenues for use in multifunctional self-powered electronic systems, including biomechanical energy harvesting and utilization, self-powered sensing and human-machine interaction.