Development of nanofiber-based flexible and hybrid nanogenerators for wearable electronics

In this project, double-effect driven nanogenerators have been developed for energy conversion between mechanical/biomechanical energy and electrical energy. In last decade, many studies have been reported in literature on piezoelectrics-triboelectric hybrid nanogenerators. However, the production of hybrid nanogenerators in these studies is based on the combination of two independently produced components at the macro level and in any way. In this study, a compact nanogenerator system was obtained by producing piezoelectric, triboelectric, and conductive components together in a single step. Here, the electrospinning method is a frequently used method in piezoelectric nanogenerators and the micro-nano structure is of great importance for triboelectric nanogenerators, making controlled production at nanoscale possible. Hybrid nanofibrous structures were obtained by simultaneous electrospinning process of poly(vinylidene fluoride) (PVDF), which is employed as piezoelectric component, and thermoplastic polyurethane (TPU) solutions. During hybrid nanofiber production, graphene oxide (GO) is fed from another nozzle, and it is ensured that the electrical energy produced in the nanofiber structure is delivered to the nanogenerator electrodes more efficiently. Up to this stage, electrospinning parameter optimization and optimization of the GO reinforcement ratio have been carried out. The originality of this project is the hybrid nanogenerator system to be formed with a hybrid nanofiber structure. In next step of study, nanogenerator output performance was improved by roughened PVDF and TPU nanofibers with determined optimum GO ratio. In the last stage of the study, it was aimed to increase the nanogenerator performance by hydrothermal growth of zinc oxide (ZnO) nanowires on the surface of the nanofibers. It has been evaluated that the vertically oriented ZnO nanowire growth on the surface of the nanofibers will both increase the contact surface area by adding the surface roughness of the nanowire-forest and strengthen the piezoelectric effect due to the use of ZnO. The output power density of the resulting nanogenerators was 16.47 mW/m2. In addition, the rechargability of commercial capacitors of different capacities with the obtained nanogenerators, and the usability of the stored energy in some electronic devices have been proven. On top of that, nanogenerators have been applied to the textile surface, proving their suitability for sensor applications.