A Janus-interface origami fog collector with spike arrays for efficient droplet transport

To meet the escalating global demand for water resources in arid regions, fog harvesting presents a promising solution especially in high-humidity regions. However, current collectors generally suffer from critical issues such as low droplet capture efficiency, difficulty in droplet retention and transportation, and poor cyclic stability. Inspired by the water-capturing abilities of bat tongues and cactus spines, a fog harvester with a folding fan structure and a spike array has been developed. These hierarchically structured surfaces, fabricated by laser etching, control wettability to capture and drive the unidirectional transport of water droplets. The spikes further allowed for the regulation of droplets to achieve transport along a Janus wettability gradient. Compared to a conventional flat aluminum sheet of the equivalent projected area, this device achieved a 403.58 % higher collection efficiency. It also exhibited remarkable cyclic stability, long-term water performance, and corrosion resistance, thereby demonstrating its potential for practical applications. This work provides an efficient strategy for sustainable fog collection.