Circadian‐Inspired Hydrogel Moisture Electricity Generation

ABSTRACT 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.