Asymmetric Bipolar Membrane for High Current Density Electrodialysis Operation with Exceptional Stability
Éowyn Lucas, Justin C. Bui, T. Nathan Stovall, Monica Hwang, Kaiwen Wang, Emily Dunn, Ellis Spickermann, Lily Shiau, Ahmet Kusoglu, Adam Z. Weber, Alexis T. Bell, Shane Ardo, Harry A. Atwater, Chengxiang Xiang
Abstract
Bipolar membranes (BPMs) enable isolated acidic/alkaline regions in electrochemical devices, facilitating optimized environments for electrochemical separations and catalysis. For economic viability, BPMs must attain stable, high current density operation with low overpotentials in a freestanding configuration. We report an asymmetric, graphene oxide (GrOx)-catalyzed BPM capable of freestanding electrodialysis operation at 1 A cm –2 with overpotentials <250 mV. Use of a thin anion-exchange layer improves water transport while maintaining near unity Faradaic efficiency for acid and base generation. Voltage stability exceeding 1100 h with an average drift of 70 μV/h at 80 mA cm –2 and 100 h with an average drift of −300 μV/h at 500 mA cm –2 and implementation in an electrodialysis stack demonstrate real-world applicability. Continuum modeling reveals that water dissociation in GrOx BPMs is both catalyzed and electric-field enhanced, where low p K a moieties on GrOx enhance local electric fields and high p K a moieties serve as active sites for surface-catalyzed water dissociation. These results establish commercially viable BPM electrodialysis and provide fundamental insight to advance design of next-generation devices.