Twisting two-dimensional photothermal sponges for boosting solar steam generation

Solar-powered evaporation emerges as a sustainable way to alleviate water stress by harvesting freshwater from diverse sources. Optimizing heat management by evaporator structures is becoming a mainstream strategy to promote solar-powered evaporation performance. In this work, we develop a novel evaporator design by simply twisting a two-dimensional polypyrrole-decorated sponge with excellent light-to-heat conversion capacity to reduce heat loss and recover environmental energy. The enlarged evaporation surface and reduced bulk water within the evaporator promote heat utilization in evaporation. The twisted structure dilutes the light density on the evaporator surface to reduce surface temperature, decreasing the driving force of heat transfer and promoting the contribution of environmental energy during evaporation. By integrating solar evaporation and environment evaporation, such an evaporator achieves an ultra-high evaporation rate of ∼4.0 kg·m−2·h−1 and an apparent evaporation efficiency exceeding 100% for 3.5 wt% saline solution. Smaller twisting angle lead to a higher calculated evaporation rate due to the reduced light density. Moreover, an evaporator array performs a high water production rate of 17.3 kg·m−2·day−1 in the outdoor experiment.