Bioinspired Pyramidal Array Photothermal Structure for Highly Efficient Water Evaporation under Omnidirectional Illumination

Solar-driven interfacial evaporation is regarded as a green and sustainable strategy to address the global freshwater crisis. Nevertheless, it remains challenging to develop a photothermal structure with highly efficient evaporation under omnidirectional illumination. Herein, a three-dimensional multiscale pyramidal array photothermal structure (PAPS) was developed from the inspiration of durian skin. It consisted of macroscale three-dimensional pyramidal array structures to enhance light absorption and increase the evaporation area, microscale porous structures to ensure continuous water transport and facilitate vapor diffusion, and nanoscale protrusion structures with hybrid photothermal materials of Cu_xO/C to enhance light trapping and photothermal conversion efficiency. It was fabricated in a porous foam matrix by a facile milling process. The PAPS induced an evaporation rate of 2.08 kg/m²h under one sun illumination under direct light conditions, which was 24% higher than that of a planar photothermal structure. The PAPS maintained fairly good evaporation performance under inclined light conditions, i.e., the evaporation rate of the PAPS was 1.72 kg/m²h at 45° inclined light angle. It only decreased by 17% compared to the direct sunlight conditions, which was much smaller than the 29% decrease of the planar photothermal structure. Additionally, the PAPS present a large evaporation rate of 6.29 kg/m²h under one sun illumination in air convection conditions with a wind speed of 3 m/s. This work provided a high-performance pyramidal array photothermal structure for highly efficient water evaporation under omnidirectional illumination, which provides potential opportunities for stable solar desalination and freshwater supply in complex and variable environments.