Radiative cooling assisted self-sustaining and highly efficient moisture energy harvesting.

Harvesting electricity from ubiquitous water vapor represents a promising route to alleviate the energy crisis. However, existing studies rarely comprehensively consider the impact of natural environmental fluctuations on electrical output. Here, we demonstrate a bilayer polymer enabling self-sustaining and highly efficient moisture-electric generation from the hydrological cycle by establishing a stable internal directed water/ion flow through thermal exchange with the ambient environment. Specifically, the radiative cooling effect of the hydrophobic top layer prevents the excessive daytime evaporation from solar absorption while accelerating nighttime moisture sorption. The introduction of LiCl into the bottom hygroscopic ionic hydrogel enhances moisture sorption capacity and facilitates ion transport, thus ensuring efficient energy conversion. A single device unit (1 cm 2 ) can continuously generate a voltage of ~0.88 V and a current of ~306 μA, delivering a maximum power density of ~51 μW cm -2 at 25 °C and 70% relative humidity (RH). The device has been demonstrated to operate steadily outdoors for continuous 6 days.