Lead-free nanocomposite piezoelectric nanogenerator film for biomechanical energy harvesting

Piezoelectric nanogenerators are attracting substantial attention due to the environmental constraints and ecological considerations of energy harvesting. However, the Achilles' heel of the majority of these nanogenerators is the presence of toxic compounds or the requirement of a poling process to promote higher piezoelectric effect. Here, a self-poled and bio-flexible piezoelectric nanogenerator (BF-PNG) is designed, based on lead-free biocompatible Ba0.85Ca0.15Zr0.10Ti0.90O3 nanoparticles that are functionalized with polydopamine and embedded in the polylactic acid biodegradable polymer. The BF-PNG can generate open-circuit voltage and short-circuit current of 14.4 V and 0.55 µA, respectively, under gentle finger tapping. Furthermore, it demonstrates an outstanding high mechanical robustness, stable and durable output even after one year. It achieves a maximum power density of about 7.54 mW/cm3 at a low resistive load of 3.5 MΩ. The feasibility of the BF-PNG by trigging commercial electronics such as charging capacitors and lighting a LED is verified, and the BF-PNG can drive a 1 µF capacitor to store the energy of 3.92 µJ within 115 s under gentle finger tapping. This research demonstrates that a lead-free piezoceramic in combination with a biodegradable piezopolymer can lead to a design of bio-flexible piezoelectric nanogenerators with outstanding performances and in particular useful in self-powered medical devices.