Hybrid Directional Radiative Cooling and Solar Heating for Efficient Water Harvesting via Interior Natural Convection

Abstract Solar evaporation has attracted lots of attention recently due to its environmental‐friendly and high efficiency, which is a promising approach for water harvesting. Yet system‐level design has been largely overlooked, limiting its water collection efficiency. Here, a passive water collection device integrating hybrid directional solar heating is presented and radiative cooling within a V‐shaped structure to enhance interior natural convection and reduce heat & mass transfer resistance. Photonics and interface engineering enable selective solar heating, and low evaporation enthalpy with a high‐water supply rate to improve water evaporation, passive daytime radiative cooling, and a superhydrophilic asymmetric channel for efficient condensation and droplet shedding. This design shows an indoor water collection rate of 2.62 kg m ⁻² h ⁻¹ under one sun (1000 W m ⁻² ) and an outdoor water collection rate of up to 2.76 kg m ⁻² h ⁻¹ under 715 W m ⁻² . These results indicated the substantial potential of a completely passive water collection system to improve heat and mass transfer behaviors via natural convection, thereby contributing to the mitigation of water scarcity.