Circadian-Inspired Hydrogel Moisture Electricity Generation

Energy harvesting from ambient moisture offers a ubiquitous solution to the energy crisis, free from geographical restrictions. While hydrogel-based moisture electric generators (MEGs) show promise as scalable sustainable energy sources, they currently face significant challenges regarding performance degradation due to inevitable water saturation or desiccation. Here, we present a circadian-inspired hydrogel MEG that exhibits sustained electricity generation by leveraging diurnal temperature-moisture fluctuations-traditionally considered detrimental noise-as a critical driving force. By combining an asymmetric hygroscopic hydrogel architecture with a conditioning treatment, the device undergoes reversible internal water redistribution, which is closely associated with periodic reversal of the effective driving force for electrical output. The resulting MEG delivers a short-circuit current density of 75 µA cm^-2, an open-circuit voltage of 0.4-1 V, and a power density of 16 µW cm^-2, consistently maintaining performance over a 57-day period. Electrical characterization, spectroscopy, and gravimetric analysis support a water-redistribution mechanism for the observed reversible electrical current. Similar behavior was also observed in several related hydrogel system. This work highlights a previously underexplored operational mode in hydrogel moisture electricity generation and offers a promising design concept for sustained ambient energy harvesting under coupled thermal-moisture fluctuations.