Supersonically Sprayed PVDF and ZnO Flowers with Built-in Nanocuboids for Wearable Piezoelectric Nanogenerators

Healthcare implant devices that can internally generate a flow of electrical charge driven by mechanical stimuli are in demand. Such self-powered electromechanical devices are known as piezoelectric nanogenerators (PENGs). In this study, a piezo-ceramic element of hydrothermally synthesized ZnO flowers comprising built-in nanocuboids was supersonically sprayed with piezo-polymer polyvinylidene fluoride (PVDF) to fabricate ZnOembedded PVDF films for flexible PENG devices. In the presence of ZnO, the catastrophic supersonic impact and shear flow transformed the nonpolar a-phase of PVDF into the polar beta-phase. The combination of ZnO flowers with built-in nanocuboids and beta-phase-rich PVDF can help enhance generated charges at interfacial sites under an applied force. The supersonically sprayed PVDF/ZnO composite exhibited a 32% increase in the beta-phase compared to that exhibited by pure PVDF prior to supersonic coating. The effective piezoelectric coefficient values (d(33)*) of the pure PVDF and PVDF/ZnO composite films were 43 and 150 pm center dot V-1, respectively; the corresponding open-circuit voltages were 1.2 and 25.5 V, respectively. These significant differences confirm the pivotal role of ZnO in increasing the beta-phase within PVDF during supersonic spraying. The form of the externally applied force and frequency were varied to evaluate the electromechanical performance of PVDF/ZnO. The energy harvesting capability of the composite was demonstrated using 33 light-emitting diodes.