Decoupling Transport of Salt Ions and Water in Hierarchically Structured Hydrogel for High Salinity Desalination

Abstract Global water scarcity demands next‐generation desalination technologies that transcend the limitations of energy‐intensive processes and salt accumulation. Herein, a groundbreaking interfacial solar steam generation system capable of simultaneous hypersaline desalination and ambient energy harvesting is introduced. Through hierarchical hydrogel architecture incorporating a central vertical channel and radial channels with gradient apertures, the design effectively decouples salt transport and water evaporation: solar‐driven fluid convection directs water outward for evaporation, while inward salt migration prevents surface crystallization and redistributes excess heat. The heat dissipation induces a sub‐ambient “cold evaporation” effect, lowering the evaporative interface temperature and enhancing ambient energy utilization. The system achieves a remarkable water evaporation rate exceeding 12 kg m −2 h −1 in a 20 wt% hypersaline environment and operates continuously for 15 h without salt accumulation. Outdoor testing demonstrates a daily water production of 67.2 L m −2 , with scalable potential for sustainable desalination and industrial brine treatment.