Transferring heat downward from the evaporation interface to accelerate solar vapor generation

Solar-driven interfacial water evaporation (SIWE) is an important strategy for addressing the world's freshwater shortage. However, the traditional evaporator typically localizes the heat to the evaporation interface. This would increase the radiative heat loss between the evaporator and the environment, resulting in a reduction in the evaporation rate. Herein, a water-energy-balanced evaporator (WEBE) is proposed by accurately adjusting the thickness of the solar absorber. The excess energy is transferred downward to preheat the water, which will be transported to the evaporation interface, instead of being dissipated to the environment. In addition, a unique T-shaped water path is introduced to reduce the contact area between the evaporation interface and the bulk water. These allow the WEBE to decrease the conductive and radiative heat losses by 16.4% in total. Importantly, the WEBE demonstrates a superior evaporation rate due to efficient thermal management and water-energy balance. Under 1 sun (at a solar flux of q = 1 kW m−2) illumination, the evaporation rate reaches 2.02 kg m−2 h−1, which is 1.21 times of the traditional evaporator. This work provides a novel and accessible approach to further increase direct solar vapor productivity for solar desalination.