Bioinspired Heterogeneous Surface for Radiative Cooling Enhanced Power-Free Moisture Harvesting in Unsaturated Atmosphere.

Abstract

The development of zero-power moisture-harvesting technology in an unsaturated atmosphere is of great significance for coping with global freshwater scarcity. Here, inspired by Pachydactylus rangei's (Namib sand gecko) ability to evade thermal radiation and harvest moisture, a power-free cooling moisture harvester (PFCMH) is fabricated using the continuous, industrialized micro-extrusion compression molding. A Luneburg lens is introduced in the PFCMH for the first time, endowing it with a high reflectivity of ≈92.9% in 0.3 to the 2.5 µm waveband and emissivity of ≈98.1% in 8-13 µm waveband, which are ≈19.2% and ≈15.4% higher than those of the unstructured radiative cooler, respectively. Consequently, a temperature reduction of ≈6.9 °C is achieved. In addition, the wettability of PFCMH is well regulated, at a contact angle of ≈153° and a rolling angle of ≈42°, enabling its surface to efficiently nucleate and transport water droplets. The synergy between the surface and interface functions endows the PFCMH with exceptional passive sub-dewpoint cooling and efficient harvesting performance. Importantly, every 1 m² of PFCMH can yield ≈294.5-490.6 kg year^-1 of water and save ≈198.7-331.0 kWh year^-1 of electricity. The PFCMH offers an environmentally, power-free, and promising solution to freshwater scarcity.