Low alkaline ion solvating membrane water electrolysis (LA ISMWE) as alternative to AEMWE

Abstract

Ion solvating membranes (ISM), especially KOH doped polybenzimidazole (PBI), are investigated for use as separator in alkaline water electrolysers.[1] Because conductivity of state-of-the-art meta-PBI membranes decreases strongly below concentrations of 3 M KOH, ISM until recently were not considered for use in AEMWE.[2]

In this work,[3-5] ISM based on sulfonated polybenzimidazole were fabricated. Owing to the presence of sulfonic acid groups, these ISM exhibit significant swelling in 1 M KOH, and show a conductivity exceeding 100 mS cm-1. The absence of quaternary ammonium groups results in excellent alkaline stability. Conductivity remains high even after 6 months of stability test in 1 M KOH at 80 °C. In comparison, four ommercial AEMs lost most of their conductivity within 30 days.[6] The electrolyser performance at 1-2 M KOH at 80 °C was stable without failure for over 500 hours, suggesting that the high alkaline stability observed in ex-situ tests is also achieved in the electrolyser.

In conclusion, the use of ISM potentially opens a pathway towards durable AEMWE systems. Furthermore, operation at 2-3 M KOH, which previously was not much investigated, is feasible. While high alkalinity reduces hydrogen crossover, activates catalysts and reduces ohmic resistance, low alkalinity reduces the risk of shunt currents in stacks and reduces alkaline degradation. Therefore, LA ISMWE (low alkalinity ion solvating membrane water electrolysis) could be a way to balance performance and durability.

[1] M. L. A. Trisno, A. Dayan, S. J. Lee, F. Egert, M. Gerle, M.R. Kraglund, J. O. Jensen, D. Aili, A. Roznowska, A. Michalak, H. S. Park, F. Razmjooei, S. A. Ansar, D. Henkensmeier, Reinforced gelstate polybenzimidazole hydrogen separators for alkaline water electrolysis, Energy & Environm. Sci. 15 (2022) 4362-4375. https://doi.org/10.1039/d2ee01922a [2] D. Henkensmeier, W.-C. Cho, P. Jannasch, J. Stojadinovic, Q. Li, D. Aili, J. O. Jensen, Separators and membranes for advanced alkaline water electrolysis, Chem. Rev. 124 (2024) 6393-6443. https://doi.org/10.1021/acs.chemrev.3c00694 [3] A. Dayan, M. L. A. Trisno, C. Yang, M. R. Kraglund, M. R. Almind, J. Hjelm, J. O. Jensen, D. Aili, H. S. Park, D. Henkensmeier, Quaternary ammonium-free membranes for water electrolysis with 1 M KOH, Adv. Energy Mater. 13 (2023) 202302966. https://doi.org/10.1002/aenm.202302966 [4] unpublished work [5] unpublished work [6] H. Khalid, M. Najibah, H. S. Park, C. Bae, D. Henkensmeier, Properties of anion exchange