Flexible and biocompatible polypropylene ferroelectret nanogenerator (FENG): On the path toward wearable devices powered by human motion

Recently, there has been tremendous research efforts on the development of energy harvesters that can scavenge energy from ubiquitous forms of mechanical energy. The most studied mechanisms are based on the use of piezoelectric and triboelectric effects. Polypropylene ferroelectret (PPFE) is introduced here as the active material in an efficient, flexible, and biocompatible ferroelectret nanogenerator (FENG) device. PPFE is charged polymers with empty voids and inorganic particles that create giant dipoles across the material's thickness. Upon applied pressure, the change in the dipole moments generate a change of the accumulated electric charge on each surface of the PPFE film, resulting in a potential difference between the two electrodes of the FENG. The mechanical-electrical energy conversion mechanism in PPFE films is described by finite element method (FEM). Further investigation of the developed device shows that the magnitudes of the generated voltage and current signals are doubled each time the device is folded, and an increase with magnitude or frequency of the mechanical input is observed. The developed FENGs is sufficient to light 20 commercial green and blue light emitting diodes (LEDs), and realize a self-powered liquid-crystal display (LCD) that harvests energy from user's touch. A self-powered flexible/foldable keyboard is also demonstrated.