Collecting the space-distributed Maxwell's displacement current for ultrahigh electrical density of TENG through a 3D fractal structure design

Triboelectric nanogenerator is an emerging technology that can convert low-frequency and irregular mechanical energy into electricity and has broad applications in the fields of distributed energy harvesting, self-powered sensing, and the Internet of Things. However, it is still a challenge to achieve high electrical energy density owing to the limited surface tribocharge density. Herein, we report a three-dimensional fractal structured nanogenerator (FSNG), which can efficiently collect the triboelectrification induced space-distributed Maxwell's displacement current, and hence largely improve the electrical energy density. The output charge density, power density, and energy density of FSNG break the record and reach up to 8 mC m(-2), 2.18 MW m(-2), and 0.39 J m(-2) cycle(-1), respectively, and can be further improved by optimizing the fractal unit. In addition, the equivalent fractal circuit models for FSNG with the same functionality are developed for a deep understanding of the FSNG. This study not only creates a new record of high electrical output of nanogenerators but also paves a more efficient way for mechanical energy scavenging toward practical applications.