Engineering of electrospun lead-free PVDF/Carbon Nanofiber-ZnO nanocomposites for enhanced piezoelectric energy harvesting and wearable sensing applications

Abstract

Poly (vinylidene fluoride) (PVDF) is a promising lead-free piezoelectric polymer; however, its low β-phase fraction and limited charge transport hinder device performance. Here, we report a dual-filler strategy that synergistically integrates surface-functionalized carbon nanofibers (CNFs) and zinc oxide (ZnO) nanorods into electrospun PVDF fibers to simultaneously enhance β-phase nucleation, dipole alignment, and charge mobility. CNFs, at an optimized loading of 0.1 wt%, form conductive stress-transfer networks, while ZnO nanorods (1.5 wt%) with polar wurtzite facets act as efficient nucleating agents, promoting α→β phase transformation through localized electrostatic fields. Systematic variation of filler concentrations revealed that the 0.1 % CNF +1.5 % ZnO composition achieved the highest β-phase content (85.6 %) and piezoelectric coefficient (d₃₃ = 36 pC/N), yielding an open-circuit voltage of 80 V and power density of 20 mW/cm³ under periodic tapping. The composite nanogenerator demonstrated stable, high-sensitivity performance in wearable sensing applications, including human joint motion monitoring. This work addresses the longstanding challenge of balancing mechanical flexibility with high piezoelectric activity in PVDF-based nanogenerators and establishes a scalable, lead-free approach for high-performance energy harvesting and self-powered sensing devices.