A critical review on polyvinylidene fluoride (PVDF)/zinc oxide (ZnO)-based piezoelectric and triboelectric nanogenerators

In this current energy crisis era, piezoelectric and triboelectric effects are emerging as promising technologies for energy harvesting. Polyvinylidene fluoride (PVDF) and its copolymers are well-known piezoelectric materials with high piezoelectric coefficients, which are widely used in flexible electronic devices. PVDF is also greatly utilized in the preparation of triboelectric layer due to its higher electronegative nature amongst common polymers. On the other hand, zinc oxide (ZnO) has been widely studied to investigate its multifunctional properties, including piezoelectricity, pyroelectricity and antibacterial activity. This versatile material can be prepared, using low cost and environmentally friendly routes, in various morphologies. Various research has already been performed to capture the synergistic effects of reinforcing ZnO within the PVDF polymeric matrix. This work first describes the basic principles of piezoelectric and triboelectric effects. Thereafter, the piezoelectric and triboelectric performances of PVDF and ZnO-based materials are briefly depicted based on their structures. Finally, the challenges and future scope associated with the mechanical energy harvesting from such materials are highlighted.