PENGs for energy harvesting in MESOC. (a) The principle of PENG generating electricity. Reproduced from permission [55]. Copyright©2021, American Chemical Society. (b) Through constant tapping, the piezoelectric generator lights up ten LEDs. Reproduced from permission [127]. Copyright©2021, Elsevier. (c) FPNG based on PVDF nanocomposite membranes. Reproduced from permission [128]. Copyright©2020, Elsevier. (d) Green composite from pomegranate peel for piezoelectric energy harvesting. Reproduced from permission [129]. Copyright©2019, American Chemical Society. (e) The piezoelectric output voltage of the PSNO film during external periodic vertical compression was obtained by pressing the PENG with a finger. Reproduced from permission [130]. Copyright©2018, American Chemical Society. (f) Voltage Generation by Finger Tapping in Nanocomposite Devices. Reproduced from permission [131]. Copyright©2018, American Chemical Society. (g) A flexible WCSPS for non-invasive measurement of pulse wave and blood pressure. Reproduced from permission [133]. Copyright©2019, Wiley. (h) Digital photographic image of the LCD switched on by the PENG device through a commercial capacitor of 4.7 μF and a bridge rectifier. Reproduced from permission [134]. Copyright©2021, American Chemical Society.