High-performance coaxial piezoelectric energy generator (C-PEG) yarn of Cu/PVDF-TrFE/PDMS/Nylon/Ag.

Coaxial type piezoelectric energy generator (C-PEG) nanofiber was fabricated by a self-designed continuous electrospinning deposition system. Piezoelectric PVDF-TrFE nanofiber as an electroactive material was electrospun at a discharge voltage of 9-12 kV onto a simultaneously rotating and transverse moving Cu metal wire at an angular velocity of ω _g  = 60-120 RPM. The piezoelectric coefficient d ₃₃ of the PVDF-TrFE nanofiber was approximately -20 pm V ^-1 . The generated output voltage (V _G ) increased according to the relationship exp(-α P) (α = 0.41- 0.57) as the pressure (P) increased from 30 to 500 kpa. The V _G values for ten and twenty pieces of C-PEG were V _G  = 3.9 V and 9.5 V at P = 100 kpa, respectively, relatively high output voltages compared to previously reported values. The high V _G for the C-PEG stems from the fact that it can generate a fairly high V _G due to the increased number of voltage collection points compared to a conventional two-dimensional (2-dim) capacitor type of piezoelectric film or fiber device. C-PEG yarn was also fabricated via the dip-coating of a PDMS polymer solution, followed by winding with Ag-coated nylon fiber as an outer electrode. The current and power density of ten pieces of C-PEG yarn were correspondingly 22 nA cm ^-2 and 8.6 μW cm ^-3 at V _G  = 1.97 V, higher than previously reported values of 5.54 and 6 μW cm ^-3 . The C-PEG yarn, which can generate high voltage compared to the conventional film/nanofiber mat type, is expected to be very useful as a wearable energy generator system.