Design of triboelectric nanogenerators featuring motion form conversion, motion rectification, and frequency multiplication for low-frequency ocean energy harvesting

Wave energy is characteristic of low frequency and reciprocal motion, but is difficult to harvest. Triboelectric nanogenerators (TENGs) have proven to have potential for wave energy harvesting and conversion. How to improve the energy harvesting and conversion efficiencies is the key issue to promote its applications. Herein, a novel wave energy harvesting model (SR-TENG) was designed, and it is comprised of a wave energy harvesting module with a composite of a screw rod and a ratchet, and an energy conversion module - rotating TENG. The SR-TENG model is able to convert the reciprocating linear motion of external excitation into reciprocating rotational motion, which increases the frequency of the electrical output, and further converts the reciprocating rotational motion into unidirectional rotational motion in the harvesting module by unidirectional locking-unlocking of the ratchet, which realizes the motion rectification and positive energy accumulation of continuous external excitation. To boost energy conversion efficiency, the energy harvesting module was skillfully combined with a rotating TENG with a larger contact area. Based on theoretical analysis and experimental verification, a correlation model between the screw rod lead and force conversion coefficient was established. In addition, the dependency of structural parameters such as rotational inertia on the motion behavior and output of SR-TENG was calculated to guide the TENG design. Finally, the model SR-TENG was optimized and tested, showing effective energy power generation from ambient wave energy by which several electronic devices were driven successfully. This study provided novel ideas for the design of TENGs used in wave energy harvesting and ultimately for its industrialization in the future. We propose a novel structural design strategy for triboelectric nanogenerators (TENGs). Leveraging the combination of screw rod and ratchet, the optimized TENGs realize form conversion and rectification of motion, and frequency multiplication.