Increasing water scarcity in the face of climate change has driven significant interest in finding low-carbon-intensity ways of generating fresh water from saline sources. Conventional membrane and thermal desalination techniques require large energy inputs that can become prohibitive as salinity increases. Alternatively, solar desalination is a well-developed passive evaporative approach but is limited seasonally and geographically by solar insolation. Here, we propose and demonstrate a passive approach to a more thermodynamically attractive phase change that can also enable desalination: freezing. We develop a system that uses passive radiative cooling to the ultimate heat sink, outer space, to freeze and desalinate salt water. We experimentally demonstrate the passive desalination of 37.3 g/L salt water to 1.88 g/L after two radiative cooling-driven freezing desalination stages with 50% recovery and 17.5 g/L salt water to 0.7 g/L with 65% recovery. Our results highlight the potential of harnessing untapped thermodynamic resources for water technologies.

面对气候变化，水资源日益短缺，这促使人们对寻找低碳强度的方法从咸水源中产生淡水产生了浓厚的兴趣。传统的膜和热脱盐技术需要大量的能量输入，随着盐度的增加，这会变得令人望而却步。或者，太阳能海水淡化是一种成熟的被动蒸发方法，但在季节性和地理上受到太阳日照的限制。在这里，我们提出并展示了一种被动方法来实现更具热力学吸引力的相变，这种相变也可以实现海水淡化：冷冻。我们开发了一种系统，该系统使用被动辐射冷却到最终的散热器，即外层空间，以冻结和淡化盐水。我们通过实验证明了 37.3 g/L 盐水的被动脱盐至 1。在两个辐射冷却驱动的冷冻脱盐阶段后 88 g/L，回收率为 50%，17.5 g/L 盐水降至 0.7 g/L，回收率为 65%。我们的结果突出了利用未开发的热力学资源用于水技术的潜力。