FABRICATION OF SnO2/MXENE/PVDF BASED EFFICIENT FLEXIBLE BIO MECHANICAL ENERGY HARVESTING DEVICE

Abstract

The escalating global energy demand, compounded by the environmental imperatives associated with the continued dependence on conventional fossil fuel resources, necessitates the urgent development and deployment of sustainable energy solutions. In this context, ambient mechanical energy harvesting technologies have garnered considerable scientific interest as viable alternatives, offering the capacity to transduce ubiquitous mechanical stimuli into exploitable electrical power. The present thesis investigates the potential of piezoelectric and triboelectric nanogenerators (PENGs and TENGs) as high-efficiency platforms for mechanical-to-electrical energy transduction, with particular emphasis on their applicability in self-sustaining, battery free microelectronic systems. These nanogenerator architectures exploit the distinctive physicochemical properties of polymeric matrices and polymer-based nanocomposite materials to recuperate energy dissipated through routine anthropogenic activities, thereby establishing a renewable and decentralized power paradigm. Accordingly, this thesis presents a systematic and comprehensive investigation encompassing the rational design, controlled synthesis, and functional application of high-performance nanogenerators directed toward sustainable energy harvesting and environmental remediation. In the first investigative phase, the influence of hydrothermally synthesized SnO2/MXene (SNMX) nanocomposite fillers, introduced at low loading levels of 0.25, 0.50, and 0.75 wt%, on the electroactive phase content and dielectric behaviour of polyvinylidene fluoride (PVDF) was systematically examined. Morphological and structural characterization revealed a modified spherulitic microstructure indicative of a substantial phase transformation, with the non-polar α-phase fraction decreasing from 52% to yield a predominant polar (β + γ) phase content of 86%. Temperature- and frequency-dependent dielectric spectroscopy, conducted over 20 Hz to 1 MHz, v

disclosed that at 25°C and 20 Hz, the relative dielectric permittivity of the 0.75 wt% SNMX/PVDF composite film was elevated approximately 25-fold relative to the pristine polymer, albeit accompanied by a high loss tangent of 2.2. A monotonic enhancement of dielectric permittivity with increasing operating temperature was observed across all composite formulations. The observed dielectric improvements are mechanistically attributed to: (a) the augmentation of the electroactive phase, which facilitates molecular dipolar reorientation under applied fields; and (b) the semiconductive SnO2 interfacial layer on MXene flake surfaces, which suppresses the formation of percolative conductive pathways while concurrently enhancing interfacial polarization via the Maxwell–Wagner–Sillars (MWS) mechanism, in addition to conventional dipolar polarization contributions. A flexible device fabricated from the 0.75 wt% SNMX/PVDF nanocomposite film demonstrated a remarkable maximum peak-to-peak output voltage of 105 V, underscoring the exceptional energy harvesting efficacy of this nanocomposite system and its significant promise for next-generation self-powered electronic applications. The second phase of this research is dedicated to the synthesis and physicochemical optimization of SnO2/MXene/PVDF ternary composite films with the objective of enhancing their structural, optical, mechanical, dielectric, and electrical characteristics. Composite films comprising 2 wt% MXene nanosheets and varying concentrations of SnO2 nanoparticles (x = 0.0, 2.0, 4.0, 6.0, and 8.0 wt%) were fabricated via the solution casting technique and systematically characterized. X-ray diffraction (XRD) analysis confirmed a phase transformation from the non-polar α phase to the electroactive polar β phase within the PVDF matrix. Fourier-transform infrared spectroscopy (FTIR) quantified an enhancement in β-phase content from 65% in pristine PVDF to 80% in the optimized 6S-MP composite film. Field-emission scanning electron microscopy (FESEM) corroborated the formation of SnO2 nanoparticles and the characteristic accordion-like morphology of the synthesized MXene, while also revealing that nanofiller incorporation induced significant morphological modifications attributable to disruption of matrix uniformity. Tauc plot analysis demonstrated a systematic reduction in both direct and indirect optical bandgap energies from 5.36 eV to 4.88 eV and from 5.11 eV to 4.61 eV, respectively, vi as a function of increasing nanofiller concentration. Mechanical characterization further confirmed improvements in tensile strength and elastic modulus. Broadband dielectric spectroscopy conducted over the frequency range of 10² to 10⁷ Hz revealed a fivefold enhancement in relative dielectric permittivity at 1 kHz for the 6S-MP composite relative to pristine PVDF, accompanied by a comparatively low loss tangent (tan δ = 0.10). Analysis of AC electrical conductivity in accordance with Jonscher's universal power law indicated a progressive increase with nanofiller loading and confirmed non-Debye relaxation behaviour. Collectively, these results establish that the 6S-MP composite film, incorporating 6 wt% SnO₂ and 2 wt% MXene, achieves an optimal balance of functional properties attributable to its elevated β-phase content, homogeneous nanofiller dispersion, and enhanced charge transport mechanisms, rendering it a promising candidate for the fabrication of flexible piezoelectric energy harvesting devices. In the subsequent phase, the optimized 6S-MP composite film was employed in the fabrication of a Flexible Composite Piezoelectric Energy Harvester (FCPEH) device utilizing a conventional electrode-composite-electrode stack architecture. Under periodic palm tapping excitation, the FCPEH device yielded a maximum open-circuit voltage (Voc) of 65 V and a peak power density of 43.8 μW/cm², performance enhancements attributed to: (a) the uniformly distributed MXene network providing an expansive interfacial area conducive to efficient charge transfer; (b) the role of SnO2 nanoparticles as heterogeneous nucleating agents promoting α to β phase transition; and (c) augmented interfacial polarization arising from the synergistic interaction of SnO2 and MXene within the PVDF matrix. The device demonstrated sustained and stable average output voltage over a continuous operational period of 1000 seconds, affirming its mechanical robustness and long-term electrical stability. The practical utility of the optimized FCPEH device was validated through its successful application in: (1) real time biomechanical motion detection, including heel strike, toe flexion, digital bending, pinching, and multi-finger tapping; (2) capacitive charging of 1 μF and 2.2 μF capacitors to 2.1 V and 1.3 V, respectively, within 80 seconds; and (3) simultaneous illumination of an eleven-LED array via palm tapping.