Extreme salt-resisting multistage solar distillation with thermohaline convection

Recent advances in multistage solar distillation are promising for the sustainable supply of freshwater. However, significant performance degradation due to salt accumulation has posed a challenge for both long-term reliability of solar desalination and efficient treatment of hypersaline discharge. Here, inspired by a natural phenomenon, thermohaline convection, we demonstrate a solar-powered multistage membrane distillation with extreme salt-resisting performance. Using a confined saline layer as an evaporator, we initiate strong thermohaline convection to mitigate salt accumulation and enhance heat transfer. With a ten-stage device, we achieve record-high solar-to-water efficiencies of 322%–121% in the salinity range of 0–20 wt % under one-sun illumination. More importantly, we demonstrate an extreme resistance to salt accumulation with 180-h continuous desalination of 20 wt % concentrated seawater. With high freshwater production and extreme salt endurance, our device significantly reduces the water production cost, paving a pathway toward the practical adoption of passive solar desalination for sustainable water economy.