Mechanistic insights into water transport in electrified desalination: Osmosis and electroosmosis decoupled.

High-salinity wastewaters pose a serious challenge for conventional desalination technologies that are fundamentally constrained by the high osmotic pressure. Electrified desalination can overcome this limitation as it is driven by an electric field rather than hydraulic pressure. However, undesired water transport through ion exchange membranes, arising from both osmosis and electroosmosis, remains a key bottleneck to their efficiency. To date, the underlying mechanisms of water transport in ion exchange membranes remain largely unexplored. In this study, we determine the water transport number of ions via streaming potential measurements, based on the framework of irreversible thermodynamics, establishing a theoretical basis for quantifying electroosmosis. We then demonstrate excellent agreement between experimental measurements of water transport and theoretical predictions, validating the robustness and accuracy of our theoretical framework. We also decouple the respective contributions of osmosis and electroosmosis to the overall water transport. Guided by these insights, we propose a previously unidentified strategy to mitigate osmotic water loss by leveraging concentration polarization to reduce the effective osmotic pressure gradient, thereby suppressing osmotic water flux and improving energy efficiency. Overall, this work advances the fundamental understanding of water transport in ion exchange membranes and provides practical guidance for optimizing electrified desalination systems for high-salinity wastewater treatment.