Bio-inspired Copper Kirigami Motifs Leading to a 2D-3D Switchable Structure for Programmable Fog Harvesting and Water Retention

Bio-inspired fog harvesting devices (FHDs) have been exploited to address water shortages. Despite the advances achieved, efficient and continuous fog harvesting is still hindered by some challenges: 1) a single mechanism appears to be insufficient to achieve optimal water collection efficiency; 2) the re-evaporation of the harvested water results in decreased water collection. In this study, inspired by the unique feature of cacti, Nepenthes alata, lotus leaves, and pinecones, a 2D-3D switchable copper sheet (SLP-SHL@SP-Cu) is reported, which results in excellent fog capture and water transport rates. During the fog harvesting process, the captured droplets transport from the tip of the top surface to the bottom under the Laplace forces (cacti spine), capillary forces (lotus leaves), and low surface energy (Nepenthes alata). Notably, the novel FHD responds in a preprogrammed manner to changes in humidity and performs a dynamic transformation from a 2D planar structure to a 3D helical structure (and in reverse), enabling efficient fog harvesting (in the 3D geometry) and water storage (in its 2D form). Thus, this study opens a new avenue for the practical applications of highly effective FHDs with increased water retention abilities.