Passive thermal management has been drawing increasing interest to alleviate the ever-increasing energy demand for electronic cooling. However, state-of-the-art passive thermal management technologies are inefficient and costly. We address these critical challenges with a sustainable, fully passive cooling strategy, which utilizes moisture desorption from a hygroscopic salt solution to extract heat to prevent devices from overheating. Our experiments demonstrated highly-efficient cooling performance with outstanding self-recovery capacity. Compared with current phase change materials (PCMs) , the strategy is highly cost-effective for large-scale deployment. The techology offers a new approach to thermal management, which can be applied in electronics, batteries, solar cells, buildings, and so forth.