Nanofluid‐Guided Janus Membrane for High‐Efficiency Electricity Generation from Water Evaporation

Abstract Harvesting electricity from widespread water evaporation provides an alternative route to cleaner power generation technology. However, current evaporation power generation (EPG) mainly depends on the dissociation process of certain functional groups (e.g., SO 3 H) in water, which suffers from low power density and short‐term output. Herein, the Janus membrane is prepared by combining nanofluid and water‐grabbing material for EPG, where the nanoconfined ionic liquids (NCILs) serve as ion sources instead of the functional groups. Benefiting from the selective and fast transport of anions in NCILs, such EPG demonstrates excellent power performance with a voltage of 0.63 V, a short‐circuit current of 140 µA, and a maximum power density of 16.55 µW cm −2 while operating for at least 180 h consistently. Molecular dynamics (MD) simulation and surface potential analysis reveal the molecular mechanism, that is, the diffusion of Cl − anions during evaporation is much faster than that of cations, generating the voltage and current across the membrane. Furthermore, the device performs well in varying environmental conditions, including different water temperatures and sources of evaporating water, showcasing its adaptability and integrability. Overall, the nanofluid‐guided Janus membrane can efficiently transform low‐grade thermal energy in evaporation into electricity, showing a competitive advantage over other sustainable applied approaches.