Metasurface Enhanced Photothermal Cement Foam for Robust and High‐Throughput Seawater Desalination

ABSTRACT Solar‐driven interfacial vapor generation provides a sustainable solution to global water scarcity, but balancing high evaporation rates, durable solar‐thermal conversion, and salt resistance remains a significant challenge. Here, we present a novel cement‐based solar evaporator (CSE) featuring a multi‐scale hierarchical pore structure, fabricated via cost‐effective vacuum casting. The CSE's metasurface comprises about 7000 aligned micro‐honeycomb pores (150 μm diameter) per square centimeter, expanding the evaporation area by 623% and enabling 96.9% broadband light absorption. Nano‐scale gel pores from cement hydration weaken water hydrogen bonds, reducing vaporization enthalpy by 80%. This synergy achieves an evaporation rate of 5.47 kg m −2 h −1 under one‐sun illumination (93.3% efficiency) and 1.90 kg m −2 h −1 under dark conditions. Moreover, the unique open‐closed dual‐pore architecture, wherein open pores enable rapid salt ion diffusion and closed pores suppress heat loss, ensures continuous seawater desalination for over 30 days without performance degradation or salt accumulation. A cradle‐to‐grave life cycle assessment (LCA) reveals a 99% reduction in environmental impact. By transforming cement, the world's most abundant construction material, into a metasurface‐engineered evaporator, this work offers a durable and scalable solution for solar desalination.