High-Performance Salt-Resistant Solar Interfacial Evaporation System Synergistically Enhanced by Donnan Effect and Directional Water Transport

Solar interface evaporation provides a sustainable and low-energy-consumption way to alleviate freshwater shortages, but the accumulation of salt at the photothermal interface during the evaporation of high-concentration brine remains the core bottleneck limiting its long-term stability. This study utilizes the ion-selective repulsion mechanism imparted by the Donnan effect to regulate the cross-interfacial migration behavior of salt ions through material design. Sodium citrate is introduced into a kappa-carrageenan@agar double-cross-linked network via noncovalent interactions to construct a polyelectrolyte hydrogel with a high density of anionic groups. Simultaneously a low-temperature ice-templating method is employed to form vertically interconnected water transport channels within the hydrogel, achieving highly efficient water transport. Benefiting from the Donnan-effect-assisted directional ion-transport pathways, the resulting evaporator achieves an evaporation rate of 2.512 kg·m –2 ·h –1 in 3.5% simulated seawater. Even under high-salinity conditions (20%), it maintains a high evaporation rate of 2.280 kg·m –2 ·h –1 together with an energy efficiency of 88.9%. Notably, no performance degradation associated with salt crystallization is observed during prolonged operation. This work demonstrates that directionally structured polyelectrolyte hydrogels based on the Donnan effect can effectively suppress interfacial salt accumulation and crystallization, thereby offering an emerging design strategy for stable and efficient solar desalination under high-salinity conditions.