Zero-Gap Alkaline Water Electrolysis Using Ion-Solvating Polymer Electrolyte Membranes at Reduced KOH Concentrations

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Membranes based on poly(2,2'-(m-phenylene)-5,5-bibenzimidazole) (m-PBI) can dissolve large amounts of aqueous KOH to give electrolyte systems with ion conductivity in a practically useful range. The conductivity of the membrane strongly depends on the concentration of the aqueous KOH phase, reaching about 10-1 S cm-1 or higher in 15-25 wt% KOH. Herein, m-PBI membranes are systematically characterized with respect to performance and short-term stability as electrolyte in a zero-gap alkaline water electrolyzer at different KOH concentrations. Using plain uncatalyzed nickel foam electrodes, the cell based on m-PBI outperforms the cell based on the commercially available state-of-the-art diaphragm and reaches a current density of 1500 mA cm-2 at 2.4 V in 20 wt% KOH at 80°C. The cell performance remained stable during two days of operation, though post analysis of the membrane using size exclusion chromatography and spectroscopy reveal evidence of oxidative degradation of the base polymer at KOH concentrations of 15 wt% and higher.
Original languageEnglish
JournalJournal of The Electrochemical Society
Issue number11
Pages (from-to)F3125-F3131
Number of pages7
Publication statusPublished - 2016

Bibliographical note

This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY,, which permits unrestricted reuse of the work in any medium, provided the original work is properly cited.


  • Alkaline
  • Membrane
  • Polybenzimidazole
  • Water electrolysis
  • Zero-gap


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