There was an almost 700% increment in Voc with Mn3O4 membranes as compared to its bulk counterpart (SI sections 3 and 5, and Table ). A linear increase in Voc was observed as the bend angle increased from 0° -50° with a step change of 10°, as shown in Figure . The inset in Figure shows a schematic representation of the bend angle of the device with a digital photograph of the cell at 30° bend. The charge storage capability of the device was additionally confirmed by charging an external capacitor (4.7 µF) connected through a full-wave bridge rectifier circuit (Figure ). A 4.7 µF capacitor was used, as it operates between the tested frequency range of 1 kHz or less in standard electronic circuits. The corresponding charge discharge characteristics of the external capacitor (4.7 μF) was recorded on application of periodical pressure of 10 N with frequency of ~5.72 Hz which is as shown in Figure . Discharge cycles were recorded of by disconnecting the FNG from the RC circuit. The FNG device was capable of charging the capacitor up to ~ 0.84 V with charging time of ~246 s (Figure ) and discharge time of ~195 s. Asymmetric charge-discharge cycles were observed. Therefore, the FNG device can be used to power small electronic devices. Figure shows a comparison of Voc of some of the recent NG devices based on dimensionally-reduced materials like oxides and chalcogenides. In comparison to the recent ZnO nanosheet-based NG device (900 mV), the maximum Voc of our cell was ~2 V (@ 10 N). Additionally, desired higher voltages can be obtained with a series connection of NGs. Here, increased voltage of ~2.4 V and ~3.6 V (positive cycle only) for 2 and 3 cells, respectively, was observed when cells were connected in a series combination (Figure ). We further used the NG as a proof of concept for sensing low pressure breathable sensors. The device showed excellent sensitivity and Voc was measured during normal breathing (walking) and exertion (running). The maximum Voc during walking was noted, persistently, to be ~1.6 V, (Figure ) whereas ~2.4 V was acquired during running (Figure ).