Abstract Solar interfacial evaporation is a promising way to generate clean water from seawater using clean, abundant, and sustainable solar energy. However, non-directionally moving water with high thermal conductivity acts inevitably as a medium for heat transfer from the surface to the bottom through heat convection, resulting in low energy efficiency and a low evaporation rate. Herein, a gradient structured composite hydrogel combining a desired functional differentiation is reported. The network sizes in the hydrogel continuously change, demonstrating an enhanced capillary effect and a direction-limited water supply capability, inhibiting the heat convection loss. In addition, the reported gradient hydrogel shows broadband light absorption, satisfactory mechanical properties under a saturated swelling state, an unusually higher water evaporation rate for brine compared with that for pure water, and an inherent ability to evaporate under both 1 sun illumination and dark environment. The proposed gradient channels to restrict the flow direction of liquid, and consequently the heat convection loss, will have an significant impact on the design of other efficient photothermal evaporation systems and even the field of mass and heat transfer.

中文翻译：

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用于高效界面蒸发的梯度结构水凝胶的方向限制水传输和抑制热对流损失

摘要 太阳能界面蒸发是利用清洁、丰富和可持续的太阳能从海水中产生清洁水的一种很有前景的方法。然而，高导热率的非定向流动水不可避免地充当了通过热对流从表面向底部传递热量的介质，导致低能效和低蒸发率。在此，报道了一种结合所需功能差异的梯度结构复合水凝胶。水凝胶中的网络尺寸不断变化，显示出增强的毛细管效应和方向限制的供水能力，抑制了热对流损失。此外，所报道的梯度水凝胶在饱和溶胀状态下显示出宽带光吸收和令人满意的机械性能，与纯水相比，盐水的水蒸发率异常高，并且在阳光照射和黑暗环境下都有固有的蒸发能力。提出的限制液体流动方向的梯度通道，从而限制热对流损失，将对其他高效光热蒸发系统的设计甚至传质和传热领域产生重大影响。