Fig. 4

The only piezoelectric nanowires/tubes-based NCG devices. The photographs and output performance of energy harvesters made of NaNbO₃ NWs (a) (reproduced from ref. [24] with permission, American Chemical Society), KNbO₃ NRs (b) (reproduced from ref. [25] with permission, IOP Publishing), BaTiO₃ NTs (c) (reproduced from ref. [30] with permission, American Chemical Society) and NWs (d) (reproduced from ref. [31] with permission, Royal Society of Chemistry)