Flexible Supercapacitor-Type Rectifier-free Self-Charging Power Unit Based on a Multifunctional Polyvinylidene Fluoride-ZnO-rGO Piezoelectric Matrix.

The development of an effective mechanical to electrical energy conversion device and its functional integration with an energy storage device for self-powered portable gadgets are cutting-edge research fields. However, the generated power and the mechanical stability of these integrated devices are still not efficient to power up portable electronics. We fabricated a rectifier-free piezoelectric nanogenerator (NG) integrated with a supercapacitor (SC). A multifunctional composite matrix was prepared by the incorporation of ultrathin (<10 nm) ZnO nanoflakes and reduced graphene oxide in polyvinylidene fluoride to enhance the piezoelectric output characteristics and mechanical stability of the device while minimizing the additional energy losses during the integration. The as-fabricated SC-based power unit through the energy conversion and storage processes showed a remarkable self-charging performance. We obtained the maximum output voltage, current density, and power density of about 44 V, 1000 nA cm, and 193.6 μW cm under the applied mechanical force of 10 N, respectively. The self-charging behavior of the device showed that it can store 1.5 × 10 mC within 100 s without resorting to a rectifier. We obtained the total energy density of about 10.34 mW h kg under palm impact. Our results present a step forward in the development of the NG and SC-based flexible and self-charging devices.