Selective ion separation in electrosorption systems: progress in material development and mechanism exploration

Water scarcity remains a critical barrier to achieving global sustainable development. Capacitive deionization (CDI) has emerged as a promising water treatment technology owing to its low energy consumption, operational simplicity, and environmental compatibility. Nevertheless, its practical deployment is hindered by substantial challenges, including inadequate ion selectivity, limited desalination performance, and insufficient system stability in complex aqueous environments. This review offers a comprehensive overview of recent advancements in CDI, with a particular focus on enhancing ion selectivity through the synergistic optimization of ion exchange membranes and electrode materials. It explores the development of monovalent-selective membranes, structural engineering of functionalized electrodes, and the refinement of operational parameters. Moreover, it elucidates the mechanisms by which emerging functional materials-such as MXenes, graphene, and Prussian blue analogs-accelerate desalination kinetics and improve cycling durability. Future directions are identified, including the design of three-dimensional composite electrodes and multifunctional membranes that integrate high selectivity with robust antifouling properties. Additionally, this review consolidates commonly used performance metrics in CDI systems. Altogether, it provides a solid theoretical framework and outlines viable technological strategies to address existing limitations, paving the way for more efficient, economical, and sustainable CDI applications.