The development of highly efficient and salt-tolerant solar evaporators for sustainable seawater desalination remains a key challenge. Interfacial solar steam generation (ISSG) has emerged as a promising technology for harnessing solar energy to produce fresh water from saline sources. In this work, using polyethyleneimine (PEI) and sodium alginate (SA) as the gel network and reduced graphene oxide (RGO) as the photothermal material, we introduced 1-butyl-3-methylimidazo- lium chloride (BMIMCl) into the gel network, stirred the mixture uniformly, and finally obtained an alginate-based composite hydrogel evaporator doped with a hydrophilic imidazolium ionic liquid (denoted as BPS-Cl) via freeze-drying. The resulting evaporator possesses an anisotropic layered porous structure and favorable water transport capability. Owing to the unique anti-polyelectrolyte effect, the BPS-Cl evaporator achieved an evaporation rate of 2.86 kg•m⁻²•h⁻¹ in NaCl solution with a mass fraction of 3.5% under one-sun irradiation, which is 12.59% higher than that in pure water (2.54 kg•m⁻²•h⁻¹). Under dark evaporation conditions, the mass change of water per unit area per unit time for BPS-Cl was measured, and the corresponding photothermal conversion efficiency was calculated to be 89.25% according to the formula. Even under high-salinity conditions (w(NaCl)=10%), the evaporation rate can reach 2.32 kg•m⁻²•h⁻¹, demonstrating excellent salt tolerance. Moreover, during a 36-hour continuous desalination test in 3.5% NaCl solution (mass fraction), the evaporator exhibited stable performance with an average evaporation rate of 2.84 kg•m⁻²•h⁻¹ and no salt deposition on the surface, highlighting its excellent salt-rejection capability. In the outdoor evaporation experiment, the average evaporation rate of BPS-Cl was stable and reached 1.92 kg•m⁻²•h⁻¹. Meanwhile, the produced fresh water was collected and the ion concentrations of the freshwater were detected, which further validated its stable freshwater production performance. This study provides a novel strategy for the design of efficient and stable solar-driven desalination systems.

Key words: ionic liquid, imidazole chloride salt, seawater desalination, interfacial solar steam