Electrochemical Ion Pumping as a New Platform for Desalination: Theory and Optimization

Abstract

Electrochemical separation is an emerging research frontier with applications spanning desalination, mineral extraction, and resource recovery. Conventional electrosorption processes for desalination often suffer from operational complexity and solution mixing induced by frequent solution switching. This dissertation addresses these limitations by advancing electrochemical ion pumping (EIP), an innovative ion separation platform that achieves pseudo-continuous operation and eliminates mixing losses. This dissertation aims to advance the understanding of EIP transport mechanisms and optimize EIP system design and operation for desalination with experiments and modeling. This dissertation first quantifies the adverse impacts of mixing due to solution switching on the performance of electrosorption-based desalination under different operation modes. The analysis shows that mixing effects cannot be fully mitigated even with state-of-the-art electrode capacities, highlighting the challenge of conventional electrosorption approaches for treating saline water. Next, a fundamental ion-transport model for EIP is developed by coupling the Nernst–Planck equation with an extended Donnan framework to describe ion transport through ion-exchange polymers and ion storage in porous electrodes. The model predicts spatiotemporal distributions of ion concentrations and potentials in the charging and discharge steps, revealing dynamic ion transport behavior in EIP not observed in conventional electrosorption or electrodialysis. Electrode design and operational parameters governing EIP desalination performance are systematically investigated by combining experiments with mathematical modeling. Optimal performance depends on electrode composition to balance ionic and electronic resistance, and EIP’s fast circuit-switching mechanism enables a narrow electrode voltage window, minimizes side reactions, and maintains compatibility with low-capacity electrodes. Finally, a multi-electrode model is developed and compared with experimental data to systematically investigate EIP stack behavior under both constant voltage and constant current operation. This dissertation establishes the fundamental ion transport theory in EIP, provides guiding principles for electrode design and operational optimization, and advances its potential for energy-efficient desalination and broader ion separation applications.