Sustainable solar distillation of hypersaline water enabled by a capillary-driven fibrous membrane with robust salt crystallization

Hypersaline water management demands low-carbon, resource-oriented technologies. Yet solar-driven interfacial evaporation is still constrained by salt accumulation at the evaporation interface, which causes pronounced performance degradation. Here, we present a capillary-driven fibrous membrane evaporator ( CFME ), achieving integration of directional water delivery, heat localization, and localized crystallization for stable evaporation. The CFME showcased remarkable apparent solar-to-vapor thermal efficiency exceeding 100% under 1 sun. Remarkably, the CFME exhibits long-term stability in 24 wt% brine, where salt crystals accumulate exclusively on the membrane exterior and remain easily detachable, allowing continuous salt harvesting and coexisting with sustained evaporation. The convection–diffusion model in the mechanism analysis reveals that the salt concentration distribution within the membrane fails to reach saturation during evaporation. Alongside the microstructural characterization and porosity analysis of the brine post-evaporation, this explains the salt-free transport pathways within the membrane and the localized crystallization mechanism. This work provides a robust and scalable strategy for low-carbon, solar-driven hypersaline wastewater treatment.