All‐Cold Evaporation under One Sun with Zero Energy Loss by Using a Heatsink Inspired Solar Evaporator

Interfacial solar steam generation is a highly efficient and sustainable technology for clean water production and wastewater treatment. Although great progress has been achieved in improving evaporation rate and energy efficiency, it's still challenging to fully eliminate the energy loss to the surrounding environment during solar steam generation. To achieve this, a novel heatsink‐like evaporator (HSE) is developed herein. During solar evaporation, the temperature on the top solar evaporation surface can be regulated by the fin structures of the HSE. For the evaporators with 5 to 7 heatsink fins, the temperature of the solar evaporation surface is decreased to be lower than the ambient temperature, which fully eliminates the radiation, convection, and conduction heat losses, leading to the absolute cold evaporation over the entire evaporator under 1.0 sun irradiation. As a result, massive energy (4.26 W), which is over 170% of the received light energy, is harvested from the environment due to the temperature deficit, significantly enhancing the energy efficiency of solar steam generation. An extremely high evaporation rate of 4.10 kg m−2 h−1 is realized with a 6‐fin photothermal HSE, corresponding to an energy conversion efficiency far beyond the theoretical limit, assuming 100% light‐to‐vapor energy conversion. A heat‐sink like photothermal evaporator is designed and fabricated to realize fully cold solar evaporation under one sun irradiation with zero energy loss and massive energy gain (equivalent to 170% of the incident light energy) from the environment. An extremely high evaporation rate of 4.10 kg m−2 h−1 with corresponding energy efficiency far beyond the theoretical limit is achieved.