Facile and Scalable Fabrication of Surface-Modified Sponge for Efficient Solar Steam Generation

Solar steam generation is a highly promising technology for harvesting solar energy and desalination. Here, a new solar steam generation system is introduced based on a surface-modified polyurethane sponge with bilayered structures for efficient solar steam generation. The top layer, coated with polydimethylsiloxane-modified graphite powder, serves as light-to-heat conversion layer with a broad optical absorption, whereas the lower part of the sponge acts as a thermal insulator with a low thermal conductivity in the wet state (0.13882 W m^-1  K^-1 ). In addition, the strong hydrophobic wettability of the top layer (water contact angle: 148°) enables self-floating behavior on water, which is beneficial for practical applications. The results show that compared with a silver-nanoparticle-doped sponge and an acid-etched sponge doped with silver nanoparticles the graphite-modified sponge (GS) exhibits the highest evaporation efficiency of 73.3 % under 1 kW m² irradiation, which is 2.6 times that of pure water and far higher than that of untreated polyurethane sponge (36.0 %). The GS shows excellent stability, and its evaporation efficiency remains unchanged even after immersion in water for one month. Based on its cost-efficient, simple, and scalable manufacturing process, excellent mechanical stability, and high recyclability, the GS shows great potential as an efficient photothermal material for a wide range of large-scale applications such as solar steam generation, light absorption, heat localization, and seawater desalination.