Intrinsic Adsorption‐Diffusion Asymmetry Enables Stable Hydrovoltaic Power Generation Under Intermittent Humidity

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Hydrovoltaic energy harvesters provide a passive strategy for converting ambient moisture into electricity. However, their electrical output often rapidly decays after the removal of humidity stimulation, limiting their operation under dynamic environmental conditions. Here, we report a polyurethane‐derived polymer hydrovoltaic energy harvester (pp‐HEH) based on a hygroscopic polymeric deep eutectic solvent (HyPU DES ). The ionic and polar sites within HyPU DES enable rapid moisture adsorption, while the coupled interactions within the polymer network regulate subsequent moisture redistribution and release. This kinetic asymmetry between rapid moisture uptake and slow post‐stimulus water redistribution enables sustained hydrovoltaic output beyond the period of external humidity exposure. At 90% RH, the pp‐HEH delivers an open‐circuit voltage of 487 mV and a current density of 1.62 µA cm −2 . After 30 min exposure to 90% RH, the device maintains a voltage response for more than 120 min under 20 ± 5% RH after humidity withdrawal. This work demonstrates a material‐level strategy for extending hydrovoltaic response windows by regulating moisture transport kinetics, providing potential opportunities for self‐powered wearable and distributed electronic systems.