A Functionally Asymmetric Janus Hygro‐Photothermal Hybrid for Atmospheric Water Harvesting in Arid Regions

Abstract Metal‐organic frameworks (MOFs) are high‐performance adsorbents for atmospheric water harvesting but have poor water‐desorption ability, requiring excess energy input to release the trapped water. Addressing this issue, a Janus‐structured adsorbent with functional asymmetry is presented. The material exhibits contrasting functionalities on either face – a hygroscopic face interfaced with a photothermal face. Hygroscopic aluminum fumarate MOF and photothermal Cu_xS layers are in‐situ grown on opposite sides of a Cu/Al bimetallic substrate, resulting in a Cu_xS‐Cu/Al‐MOF Janus hygro‐photothermal hybrid. The two faces serve as independent “factories” for photothermal conversion and water adsorption‐desorption respectively, while the interfacing bimetallic layer serves as a “heat conveyor belt” between them. Due to the high porosity and hydrophilicity of the MOF, the hybrid exhibits a water‐adsorption capacity of 0.161 g g⁻¹ and a fast adsorption rate (saturation within 52 min) at 30% relative humidity. Thanks to the photothermal Cu_xS, the hybrid can reach 71.5 °C under 1 Sun in 20 min and desorb 97% adsorbed water in 40 min, exhibiting a high photothermal conversion efficiency of over 90%. Cu_xS‐Cu/Al‐MOF exhibits minimal fluctuations after 200 cycles, and its water‐generation capacity is 3.21 times that of powdery MOF in 3 h in a self‐designed prototype in one cycle.