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Published November 25, 2020 | Supplemental Material
Journal Article Open

Understanding Multi-Ion Transport Mechanisms in Bipolar Membranes

Abstract

Bipolar membranes (BPMs) have the potential to become critical components in electrochemical devices for a variety of electrolysis and electrosynthesis applications. Because they can operate under large pH gradients, BPMs enable favorable environments for electrocatalysis at the individual electrodes. Critical to the implementation of BPMs in these devices is understanding the kinetics of water dissociation that occurs within the BPM as well as the co- and counter-ion crossover through the BPM, which both present significant obstacles to developing efficient and stable BPM-electrolyzers. In this study, a continuum model of multi-ion transport in a BPM is developed and fit to experimental data. Specifically, concentration profiles are determined for all ionic species, and the importance of a water-dissociation catalyst is demonstrated. The model describes internal concentration polarization and co- and counter-ion crossover in BPMs, determining the mode of transport for ions within the BPM and revealing the significance of salt-ion crossover when operated with pH gradients relevant to electrolysis and electrosynthesis. Finally, a sensitivity analysis reveals that the performance and lifetime of BPMs can be improved substantially by using of thinner dissociation catalysts, managing water transport, modulating the thickness of the individual layers in the BPM to control salt-ion crossover, and increasing the ion-exchange capacity of the ion-exchange layers in order to amplify the water-dissociation kinetics at the interface.

Additional Information

© 2020 American Chemical Society. Received: July 14, 2020; Accepted: October 23, 2020; Published: November 10, 2020. This material is based on work performed at the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under award number DE-SC0004993 and the National Institutes of Health under grant no. S10OD023532. J.C.B. acknowledges funding from the National Science Foundation Graduate Research Fellowship under grant no. DGE 1752814. The authors would also like to thank David Vermaas, Philomena Weng, and Andrew Crothers for insightful and fruitful discussions regarding the nature of ionic transport in bipolar membranes. The authors declare no competing financial interest.

Errata

Correction to "Understanding Multi-Ion Transport Mechanisms in Bipolar Membranes" Justin C. Bui, Ibadillah Digdaya, Chengxiang Xiang, Alexis T. Bell, and Adam Z. Weber. ACS Applied Materials & Interfaces Article ASAP; DOI: 10.1021/acsami.1c07630

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