Round-the-clock atmospheric water harvesting via dual-mode radiative cooling and phase-change thermal regulation

Scalable, passive, and round-the-clock atmospheric water harvesting (AWH) remains challenging due to diurnal energy asymmetry and insufficient nighttime driving force. Here, we report a dual-mode synergistic AWH device integrating hemispherical optical design, passive radiative cooling (RC), and phase-change thermal control (TC) to enable uninterrupted day-night water production. The RC layer provides a persistently low-temperature condensation surface with high solar reflectivity (∼0.95) and atmospheric window emissivity (∼0.98). The TC layer stores solar heat during the day and releases latent heat at night to stabilize internal vapor pressure and dew point. Outdoor experiments show the system achieves a water yield of 0.116 kg·m^-2·h^-1, 214% higher than a bare hemispherical AWH, with 1.7× nighttime improvement over an RC-only device. The total condensation efficiency reaches 77.3% of the theoretical limit. After 500 h of accelerated UV aging, both layers retain stable optical and thermal properties. This strategy offers a reliable pathway for off-grid, all-weather freshwater production in mid-to-high latitude and water-scarce regions.