NH2-Functionalized Reduced Graphene Oxide-Induced β-Phase Enhancement in Electrospun PVDF Nanofibers for Self-Powered Triboelectric Sensing and Athlete Motion Monitoring

Abstract Electrospun poly(vinylidene fluoride) (PVDF) nanofibers are promising for flexible self-powered sensing, but controlling the electroactive crystalline phase while maintaining suitable morphology and mechanical integrity remains challenging. Here, amino-functionalized reduced graphene oxide (NH2-rGO) was incorporated into electrospun PVDF nanofibers to regulate crystalline structure and triboelectric sensing performance. NH2-rGO promoted β-phase formation, with the highest Fourier transform infrared (FTIR)-derived β-phase fraction of 81.6% obtained at 3 wt % loading. This phase evolution results from the combined effects of electrospinning-induced molecular orientation and NH2-rGO-mediated interfacial interactions. Frequency-dependent dielectric measurements further showed that NH2-rGO enhanced the dielectric response and interfacial polarization of the composite membranes. Considering β-phase fraction, crystallinity, dielectric response, fiber morphology, filler dispersion, and mechanical properties, the PVDF/3 wt % NH2-rGO membrane provided the best overall balance and was selected for sensing. The resulting self-powered triboelectric sensor generated reproducible signals under different mechanical stimuli, enabled real-time monitoring of plantar, knee, and elbow motions, and maintained stable responses over 3000 cycles. These results demonstrate a practical strategy for developing flexible PVDF-based wearable motion sensors without relying on external power supplies and with good cyclic repeatability for wearable applications.