Asymmetric Bipolar Membrane for High Current Density\nElectrodialysis Operation with Exceptional Stability

Bipolar membranes (BPMs) enable isolated\nacidic/alkaline regions\nin electrochemical devices, facilitating optimized environments for\nelectrochemical separations and catalysis. For economic viability,\nBPMs must attain stable, high current density operation with low overpotentials\nin a freestanding configuration. We report an asymmetric, graphene\noxide (GrOx)-catalyzed BPM capable of freestanding electrodialysis\noperation at 1 A cm<sup>–2</sup> with overpotentials <250\nmV. Use of a thin anion-exchange layer improves water transport while\nmaintaining near unity Faradaic efficiency for acid and base generation.\nVoltage stability exceeding 1100 h with an average drift of 70 μV/h\nat 80 mA cm<sup>–2</sup> and 100 h with an average drift of\n−300 μV/h at 500 mA cm<sup>–2</sup> and implementation\nin an electrodialysis stack demonstrate real-world applicability.\nContinuum modeling reveals that water dissociation in GrOx BPMs is\nboth catalyzed and electric-field enhanced, where low p<i>K</i><sub>a</sub> moieties on GrOx enhance local electric fields and high\np<i>K</i><sub>a</sub> moieties serve as active sites for\nsurface-catalyzed water dissociation. These results establish commercially\nviable BPM electrodialysis and provide fundamental insight to advance\ndesign of next-generation devices.