Janus Nano‐Micro Structure‐Enabled Coupling of Photothermal Conversion, Heat Localization and Water Supply for High‐Efficiency Solar‐Driven Interfacial Evaporation

Abstract Photothermal conversion, heat localization and water supply are the keys to achieving efficient solar‐driven interfacial evaporation. However, effective coupling between the three aspects at the air/liquid interface remains challenging. Herein, Au@Ag‐Pd trimetallic nanostructure/polystyrene (PS) microsphere Janus structures are designed as the solar absorber and thermal insulator. The Janus structures deposited on a water supply layer act as a 2D interfacial solar evaporator. The PS microsphere localizes heat at micrometer scale and enhances plasmonic absorption of the Au@Ag‐Pd nanocrystals supported on the microsphere. Meanwhile, the Janus structures divide the surface of water supply layer into multiple regions with sub‐micrometer depths, lowering the evaporation enthalpy. Owing to the synergic effects of these components, the evaporator realizes a solar‐to‐vapor conversion efficiency of 99.1% and an evaporation rate of 3.04 kg m −2 h −1 in pure water under 1 sun illumination. The efficient solar‐driven evaporation can last for over 40 h. Furthermore, the solar evaporator shows high‐performance seawater desalination with salt removal ratios of near 100%. This study brings new insights for controlling evaporation thermodynamics and kinetics. The Janus nano‐micro structure design can be extended to other systems for various solar‐thermal applications.