ZnO@Ag modified piezoelectric fibers for higher sensitivity and enhanced energy harvesting

Piezoelectric polyvinylidene fluoride (PVDF) based piezoelectric materials are good candidates for energy harvesting devices and sensing systems. Improving the piezoelectric sensitivity of the electro-spun PVDF fibers is still challenging and highly desirable. In this work, ZnO@Ag nanoparticles were synthesized and utilized as surface modifier to generate a hierarchical structure on the fiber surfaces to construct a flexible and piezoelectric three-phase coupling sensor. The effects of the atomic ratio of Ag:ZnO, surface morphology and particle concentration of ZnO@Ag nanoparticles on the β-phase content, piezoelectricity, wettability and mechanical stability of the sensor device were systematically investigated. The elastic modulus of ZnO@Ag/PVDF membrane is 0.01322 GPa, which is close to that of human skin 0.0188 GPa. Due to synergistic effect of the enhanced electrostatic field polarization and surface hierarchical structure, the ZnO@Ag/PVDF piezoelectricity sensor possessed voltage and current outputs of 15.0 Vpp and 1.775 μA respectively, which were 3.5 and 5.4 times higher than pure PVDF-based sensor. The sensitivity of the ZnO@Ag/PVDF nanofiber-based sensor was 2.422 V/kPa, which was 14.4 times higher than that of pure PVDF-based sensor. The sensor has a fast response/recovery time of 30/45 ms. The sensor can accurately detect various physiological strain signals such as cantilever oscillatory excitation, finger press, or walking behavior, and can light-up several light-emitting diodes (LEDs) and charge a capacitor (20 μF) in a short period (2.41 V in 5 Sec). This fiber-based energy harvesting and pressure sensor demonstrates promising applications in self-powered flexible wearable electronic devices in healthcare and home-care fields.