Water vapor increases the electrical conductivity of silk cocoons, human hair, jute, and corn silk. This phenomenon is unclear. In the present study, XPS analysis of cocoons showed that water vapor reduces the surface presence of low-energy carbon species (C-C, C-H). In contrast, electron-dense, high-energy carbon species (C-N, C=C, C=O) remained unchanged, possibly enhancing surface charge hopping. While water vapor improves the conduction, the deficiency of charge carrier diminishes the effect. We increase the charge carrier by soaking the cocoon in an aqueous solution of common salt (NaCl) to amplify the current. Salt treatment followed by 2-min exposure to water vapor results in a sharp upward spike in the current (3.6 ± 1.07 mA, n = 12; mean ± SE) from the baseline (0.06 ± 0.02 mA, n = 12). After 1 h, it maintains an average value of 0.39 ± 0.12 mA; n = 12, indicating an upward shift in the baseline. Every time the cocoon charges with water vapor, the next charging cycle initiates after the cocoon dries up. Inspired by the cocoon ecology, we demonstrate an alternating 'water vapor-dry air' cycle for rapid charging and discharging of the cocoon battery. Finally, we designed a prototype of a self-lighting kettle and water-vapor panels for futuristic homes using a 'brine-silk cocoon protein bio-battery,' where moist waste heat generates electricity.
© 2022. The Author(s).