A tunable flow-through membrane electrode platform for selective ion removal and enrichment

We developed a selective ion transport system based on a Pt/Ti-coated polytetrafluoroethylene membrane integrated into a flow-through membrane electrode (FTME). The membrane provided both electrical conductivity and chemical stability, thereby enabling modulation of ion concentration in a continuously flowing NaNO3 solution under an applied electric field. By varying the field direction, the system enabled selective removal or enrichment of ions, with negative fields facilitating removal and positive fields promoting enrichment. The extent of concentration change varied systematically with the electric field strength, highlighting the system's tunable selectivity. Based on experimental observations, we proposed a selective ion transport mechanism governed by electrostatic interactions and directional ion migration within the FTME-integrated system. The transport behavior remained consistent across multiple cycles, confirming stable performance under continuous flow. This FTME-based platform offers a controllable approach for selective ion separation and enrichment, with promising applications in water purification, desalination, and rare-earth recovery.