A leaf-like photothermal evaporator with enhanced thermal conduction in reversed solar-driven desalination for efficient freshwater harvest

Solar-driven desalination has received tremendous attention due to its utilization of renewable solar energy, minimized carbon footprint, and simple installation. However, the traditional solar evaporator has the disadvantages of damaged light absorption and low heat transfer efficiency. In this work, a leaf-like photothermal evaporator (LPE) is designed by integrating the functions of light-to-heat conversion, water transport and evaporation, and vapor discharge. The photothermal layer is made of graphene oxide reduced by tannic acid, which shows a full–spectrum optical absorption as high as 94 % and achieves a strong combination with the water transport-evaporation layer thereby improving the heat conduction. Due to the chemical and mechanical bonding between tannic acid and cellulose, the temperature difference between the photothermal layer and the water transport-evaporation layer was reduced by 33 %. In addition, the water transport-evaporation layer adopts a Janus structure, which makes the water transport-evaporation layer thinner, thereby reducing the heat loss during the water transporting process, and provides a hydrophobic surface with good resistance of salt precipitation. By combing with an aluminum-made invert-structured condenser, a reversed solar-driven desalination (RSDD) system is proposed, whose water collecting rate is greatly improved to be 1.007 kg m −2  h −1 . A freshwater collection efficiency as high as 80 % is almost the highest value of a single-stage solar distiller. Besides, a single-stage solar distiller with four LPEs in parallel is made and applied in the outdoor desalination. This work proposes a design idea for a new type of solar distillation system, which will play a role in response to the water crisis.