Strain gradient effect in ZnWO4-nanorod/PVDF piezoelectric nanogenerators prepared by supersonic cold spraying

The performance of a piezoelectric nanogenerator can be improved through the use of polyvinylidene fluoride (PVDF) containing randomly distributed ZnWO₄ nanorods, which localizes polarization and accommodates a greater strain gradient between the nanorods and PVDF matrix when force is applied. The irregular nanorod alignment facilitates their nonuniform deformation when externally moved, thereby enhancing the strain effect and the output potential as a consequence. Increasing the tapping force and frequency enhances the piezopotential, which is attributable to improved charge separation and rapid force distribution. The optimal sample containing 0.3 g/g_PVDF ZnWO₄ nanorods demonstrated enhanced performance by delivering an output voltage of 21.6 V, a maximum power of 120 μW, and 100 % electromechanical stability for over 8400 cycles, with an effective piezoelectric coefficient of 41.8 pm·V⁻¹ determined by piezoresponse force microscopy. The optimal piezoelectric nanogenerator generates voltage in response to various external movements, including walking, running, and finger/elbow bending, and is able to power a light-emitting diode, thereby demonstrating its potential in health-monitoring and sports-related portable-device applications.