Solar Steam Generator with Divergent Microchannels for Highly Efficient and Salt-Resistant Brine Evaporation

A novel solar steam generator featuring divergent microchannels (SSG-DM) is developed via directional freezing of a polypyrrole (PPy)-cellulose nanofiber (CNF) suspension in an inverted frustum mold. Contrary to the conventional 3D SSGs characterized by random micropores (SSG-RM), SSGs incorporating vertical microchannels (SSG-VM), fabricated through directional freezing procedure, demonstrate increased evaporation performance due to enhanced water transport to the top surface. However, SSG-VM manifests a limitation in the form of reduced salt resistance on its side surfaces where water transport is restricted. This issue is addressed by directional freezing of a PPy-CNF suspension in an inverted frustum mold, followed by freeze-thawing gelation in an AlCl3 solution. The fabricated SSG features divergent microchannels that spanned from the bottom surface to the top and side surfaces, with a gradual increase in diameter. The evaporation rate of SSG-DM is recorded at 2.42 kg m-2h-1 under 1-sun illumination; this rate further increases to 15.73 kg m-2h-1 in the presence of a 4 m s-1 wind. Notably, SSG-DM demonstrates excellent salt resistance in highly saline brine (10 wt%) under windy conditions (4 m s-1), whereas SSG-RM and SSG-VM are ineffective under the same conditions. A solar steam generator with divergent microchannels (SSG-DM) is developed via directional freezing in an inverted frustum mold. Divergent microchannels facilitate water transport to both the top and side surfaces, enabling highly efficient and salt-resistant brine evaporation under windy conditions. The evaporation rate of SSG-DM reaches 15.73 kg m-2h-1 in the presence of wind. image