Fig. 1: Design and structural characteristics of the fully stretchable hydrovoltaic cell (FSHC) based on carbon nanotube (CNT) fibers.

a Schematic illustration of the FSHC fabrication process, comprising (i) prestraining of an elastomeric core (200% elongation), (ii) helical winding of neat CNT (NCNT) and oxidized CNT (OCNT) fiber electrodes around the prestrained core, and (iii) strain relaxation, where the elastomeric core returns to its original dimensions and induces self-locking of the CNT fibers onto the elastomeric core. When exposed to water, the FSHC generates electricity through hydrovoltaic effects, in which interactions between water molecules and the CNT fiber surfaces create a potential difference (inset). Water image from the Freepik website, which provides free stock photos licensed. Optical micrographs showing (b) the uniform parallel double-helix configuration of the FSHC (scale bar, 500 µm), c the constant interstitial spacing between the helical CNT fiber electrodes (scale bar, 150 µm), and d the intimate contact interface between the CNT fibers and the elastomeric core, formed by the winding-lock mechanism (scale bar, 100 µm). Here and elsewhere, red and blue shades are used to differentiate the individual CNT fiber electrodes. e Photograph of the completed FSHC demonstrating flexibility, with an inset showing the Fermat spiral configuration. f Cyclic loading–unloading curves under 200% strain, which demonstrate excellent elastic recovery, with an inset showing stress–strain curves before (black) and after (blue) the 100th cycle. g Time-dependent strain and resistance variations of the FSHC during cyclic stretching and releasing at 200% strain.