Construction of a high-efficiency piezoelectric nanogenerator based on in situ polarization of PVDF nanofiber films by electrospinning

Because of the global fossil energy crisis and environmental pollution problems, the efficient use of green, renewable, and clean energy has become a major trend. Mechanical energy is considered an ideal alternative energy source because of its abundance, accessibility, and non-polluting characteristics. A piezoelectric nanogenerator (PENG) can convert environmental mechanical energy into electrical energy to power electronic devices. However, conventional piezoelectric materials must induce dipole alignment by electrical polarization to obtain piezoelectric properties, which substantially increases the cost and energy consumption of device preparation. Meanwhile, depolarization occurs when the external electric field is removed, which severely affects the performance of the piezoelectric material. In this study, PVDF nanofiber film is prepared using the electrospinning method. The PVDF dipole is rearranged to achieve in situ polarization by a strong electric field and stretching force generated by the electrospinning process. The PVDF nanofiber film process has a high electroactive β-phase content of 78.7%, which is the main contributor to the piezoelectric properties. The PENG constructed based on this film achieves direct conversion of mechanical energy to electrical energy, greatly improving energy use. The open-circuit output voltage of the thin film PENG prepared based on the electrostatic spinning method is 1.6 V, and the short-circuit output current is 0.14 μA, which are 4.5- and 2.6-fold higher than those prepared using the spin-coating method, respectively. The PVDF–PENG can charge a 1-μF capacitor to 2 V through a bridge rectifier after 60 s of human finger tapping. The power density of the PVDF–PENG is analyzed by measuring the electrical parameters at both ends of the resistor. The maximum output power is 0.03 μW at an applied load of 200 MΩ. More electrical energy can be obtained based on the PVDF–PENG, which further illustrates its possibilities and reliability in practical applications. Further, the PVDF–PENG maintains approximately 100% output capacity after 2000 consecutive cycles of compression, verifying its long-term stable service capability. Finally, the energy collected from the mechanical energy of human motion by the PVDF–PENG is explored to drive low-power consumer electronics. Six commercial LEDs are lit by using a large PENG without using any storage device. In addition, a bridge rectifier is used to charge a 2.2-μF capacitor, which successfully lights up a commercial electronic watch.