High-Performance Magnesium–Carbon Nanofiber Hygroelectric Generator Based on Interface-Mediation-Enhanced Capacitive Discharging Effect

This study reports the concept of a water/moisture-induced hygroelectric generator based on the direct contact between magnesium (Mg) alloy and oxidized carbon nanofibers (CNFs). This device generates an open-circuit voltage up to 2.65 V within only 10 ms when the unit is placed in contact with liquid water, which is higher than the reduction potential of magnesium. The average peak short-circuit current density is ∼6 mA/cm², which is among the highest values yet reported for water-induced electricity generators. Our results indicate that galvanic corrosion occurs at the interface between the CNF and Mg electrode, but the device can still generate electricity because of the high contact resistance caused by the work function difference between Mg and CNF and the surface oxidation. The oxidized CNF is shown to absorb water/moisture and get reduced, leading to a capacitive discharging effect to provide enhanced signal amplitude and sensitivity. These devices are found to be highly sensitive to small quantities of water, and their high output voltage and current make them useful for the detection of water vapor in the human breath as well as changes in ambient humidity. The Mg/CNF systems thus provide a new technology for use in the fabrication of self-powered water/moisture sensors and the development of portable electric power generators.