Janus Membranes for Osmotic Energy Harvesting and Flow Capacitive Deionization

The conversion of osmotic energy from salinity gradients into electricity offers a sustainable and low‐intermittency source of clean power, capable of complementing existing energy systems. Membrane properties are central to the efficiency of such energy conversion; however, conventional ion‐exchange membranes often suffer from high internal resistance and limited performance. In this work, we report a Janus membrane engineered from a microporous sulfonated poly(ether sulfone) base coated with a thin, nano‐porous, positively charged crosslinked poly(vinyl alcohol)–poly(ethyleneimine) layer. The asymmetric architecture promotes directional ion transport, selectivity, and reduced resistance, leading to high osmotic energy harvesting. The membrane achieved a maximum power density of 0.38 W m −2 and a current density of 18 A m −2 under a 50‐fold KCl concentration gradient at ambient temperature. The power density further increased to 0.705 W m −2 upon introducing a 30 °C temperature differential, attributed to enhanced ion mobility and improved surface‐charge regulation. In flow capacitive deionization applications, the Janus membrane exhibited an excellent salt adsorption capacity of 4.21 mg g −1 at 1.2 V in 1 g L −1 NaCl solution, demonstrating efficient desalination performance. These results highlight the potential of the developed asymmetric Janus membrane as a cost‐effective and robust platform for simultaneous osmotic energy harvesting and water desalination.