Co 0.05 ‐Bi 2 S 3 /CF Photothermal Layer Integrated With Freeze‐Cast Alumina Vertical Channels for Efficient Interfacial Solar Desalination

ABSTRACT Sustainable freshwater production is one of the main issues for modern societies, and solar desalination is expected to play a significant role in the matter. Interfacial solar desalination is an emerging technology that demands highly efficient photothermal materials to absorb solar radiation and transport salty water from water reservoir to the hot surface, where sunlight absorption takes place, minimizing heat dissipation. In this study, a bicomponent solar‐driven interfacial evaporator made of Co 0.05 ‐Bi 2 S 3 /carbon foam (CF) (photothermal material) on a porous alumina substrate having vertically aligned microchannels was explored. The freeze‐casting technique allowed the preparation of a highly porous substrate (bulk porosity π b = 0.85) characterized by a low thermal conductivity ( k = (1.14 ± 0.06) W m −1 K −1 ). Moreover, the vertically aligned pores and the high fraction of open porosity ( π a = 97.7%) allowed for a fast water uptake along the sample (14 mm height in 5 s), making it a good candidate as a substrate for solar‐driven interfacial evaporation. The porous structure characterized by long vertical channels obtained through the freeze‐casting technique allowed for the preparation of thick samples without compromising the water transport capacity and ensuring a better heat confinement at the phase–change interface, leading to high performance. The best performing device showed an evaporation rate of (2.6 ± 0.2) kg m −2 h −1 , a value higher than most of the results found in the literature, making the sample a promising candidate for further studies thanks to the simplicity of preparation, the use of cheap materials, and the scalability of the applied technologies.