SYNTHESIS, FABRICATION, AND CHARACTERIZATION OF POLYMERS- CARBON BASED FLEXIBLE NANOGENERATOR FOR ENERGY HARVESTING APPLICATIONS

Abstract

The rapid surge in global energy demand, coupled with environmental concerns linked to usage of conventional fossil fuels, underscores the need for sustainable energy solutions. Energy harvesting technologies have emerged as promising alternatives for addressing these challenges, enabling the conversion of ambient mechanical energy into usable electrical power. This thesis explores the potential of piezoelectric and triboelectric nanogenerators (PENG and TENG) as an efficient platform for harvesting mechanical energy to power small electronic devices, particularly in self-sustaining, battery-free applications. These nanogenerators leverage the unique properties of polymers and polymers-carbon based nanocomposite materials, transforming wasted energy from daily activities into a renewable power source. Furthermore, by incorporating a piezoelectric material as one of the components in a triboelectric nanogenerator, both effects can work together. This hybrid approach not only amplifies the electrical output but also broadens the range of mechanical energies it can capture, making the device highly versatile for applications that require reliable, self-sustained power sources in environments with diverse energy sources, such as wearable electronics, IoT devices, and environmental remediation applications. With this aim, the present thesis provide a comprehensive study on the design, synthesis, and application of high-performance nanogenerators for sustainable energy harvesting and environmental remediation applications. The first part of the research focuses on a piezoelectric nanogenerator (PENG) based on polyvinylidene fluoride (PVDF) and heteroatom-doped reduced graphene oxide (rGO) with boron (B), nitrogen (N), and boron-nitrogen (BN) codopants. The integration of these doped rGO variants into the PVDF matrix significantly enhances the piezoelectric response of the nanocomposite films. Among them, the PVDF/BN-rGO based nanogenerator demonstrates the highest output, achieving highest voltage and current of 20.4 V and 15.9 μA, which are substantially higher than those of pristine PVDF. Frequency-dependent analysis reveals optimal performance at 6 Hz. Moreover, increased β-phase content in PVDF is ascribed due to the formation of a conductive network that enhances charge transfer. This PENG effectively converts biomechanical energy from human motions such as finger tapping, wrist bending, and elbow folding into electrical power. To further enhance the output, a hybrid nanogenerator (HNG) was developed by layering the PVDF/BN-rGO nanocomposite with a PDMS thin film, combining piezoelectric and triboelectric Ph.D. Thesis (Shilpa Rana) vi effects. The hybrid configuration achieved an impressive output voltage of 57.6 V, which was sufficient to charge capacitors, light LEDs, and power a calculator. This study introduces a promising approach to enhance the nanogenerator performance for self-powered wearable electronics by utilizing graphene derivatives as nanofillers. Further, the effects of rGO, nitrogen-doped rGO (N-rGO) concentration and electrospinning technique on the output of PVDF-based triboelectric nanogenerators (TENGs) was studied. The optimal nanofiller concentration was identified at 1.5 wt% of rGO and N-rGO, where the PVDF nanocomposite demonstrated the highest output of 156 V, approximately double that of pristine PVDF. However, performance declines at higher concentrations due to the formation of conductive networks within the matrix. Nanofiber mats produced by electrospinning yielded even greater enhancements, with the PVDF/N-rGO nanofiber-based TENG reaching a peak output voltage of 368 V and a power density of ~282.8 μW/cm². The study also reveals that both tapping frequency and impact force significantly influence output, with increased frequency and force boosting charge transfer and capacitance. Finite element analysis was performed to provide quantitative insight into surface potential distribution. Subsequently, the capability of the fabricated TENG was demonstrated by successfully powering small electronic devices and functioning as a self-sustained motion sensor, capable of automatically turning on light in response to human movement at night. This highlights its promising applications in advance human-machine interfaces and wireless sensing technologies. Finally, to broaden the applications of TENGs, PVDF nanofibers incorporated with boron-nitrogen codoped rGO (BN-rGO) were utilized for energy harvesting and environmental remediation. The optimal performance was achieved with a BN-rGO concentration of 1.5 wt%, resulting in maximum outputs of 380 V, 36 μA, and 336 μW/cm². The study also investigated the effect of various counter triboelectric layer materials, including PTFE, PDMS, PET, paper, and nitrile gloves, replacing nylon. It has been found that TENG based on PVDF/BN-rGO and nylon demonstrated superior output, which may be attributed to the greater electronegativity difference between PVDF/BN-rGO and nylon. Thereafter, a self-powered system using a TENG as power source was developed for degrading methylene blue in wastewater. While the TENG alone required 12 hours for complete dye degradation, the addition of a BN-rGO as an catalyst significantly reduced the time to 100 minutes. This research provides an effective strategy for developing high-performance TENGs for sustainable applications in energy harvesting, self-powered sensing, and environmental remediation.