Effect of folding on 3D photothermal cones with efficient solar-driven water evaporation

Efficient management of solar irradiation into exploitable thermal energy for fast generation of clean water has been the recent focus. However, the solar-driven evaporation is generally limited to the unidirectional evaporation, and the production rate is still low and further efforts are still required in order to enhance light harvesting and evaporation efficiency. Polypyrrole (PPy) was previously coated on polymer cone to demonstrate its superior light absorption and conversion caused by the multiple reflections of incident light inside the cone's cavity. Instead of plane polymer cone, folded cones made of inexpensive, ready-available filter paper were used in this study to prove the effect of increasing folds in enhancing the light absorbance and heat conversion. As fold increases the reflection area inside the cone, the light-to-heat and the solar conversion efficiency are therefore increased with the increase of fold on the paper cones. The solar conversion efficiency of the cone with 32 folds reached 83.9% under one sun illumination, which is higher than the plane cone. Practical application of desalination of the folded cone also was demonstrated in this study. Based on the present result, 3D structure of the photothermal material is important in controlling final performance of the solar-driven water evaporation device and the idea of using folded structure can be applied to other photothermal materials, thus providing foundation for developing novel solar-driven water evaporation device.