Flow-synchronized ring-shaped electrochemical ion pumping for redox-free desalination without terminal electrodes

Abstract Electrochemical systems offer a modular and tunable approach to chemical and environmental separations. However, their deployment at small scale is often hindered by the reliance on reactions at terminal electrodes, which introduce gas evolution, pH shifts and energy losses. Here we introduce flow-synchronized ring-shaped electrochemical ion pumping, which eliminates terminal electrodes entirely by arranging ion-shuttling electrodes in a ring configuration and synchronizing the switching of circuit and flow. We show that a ring configuration alone without synchronized flow switching fails to induce net ion transport because of potential symmetry. This challenge was resolved by introducing alternating air gaps that isolate inactive circuits, thereby breaking potential symmetry and enabling pseudo-continuous unidirectional ion flux. Flow-synchronized ring-shaped electrochemical ion pumping achieves effective desalination using a single power source, demonstrating high current efficiency and energy efficiency superior to state-of-the-art electrodialysis and capacitive deionization at the same scale and under comparable conditions.