Polybenzimidazole anion-exchange membranes for the iron-chromium redox flow battery

du Toit JP, Atanasov V, Cho H, Kerres J, Wagner M, Krieg HM (2026)

Publication Type: Journal article

Publication year: 2026

Journal

Journal of Energy Storage Elsevier

Book Volume: 182

Article Number: 124419

DOI: 10.1016/j.est.2026.124419

Abstract

The perfluorinated sulfonic acid (PFSA) cation exchange membranes (CEMs), Nafion™, currently employed in the iron-chromium redox flow battery (ICFB) face selectivity challenges at elevated operating temperatures of 65 °C, while contributing significantly to the CAPEX cost of the technology. Before the ICFB can feasibly be scaled up toward a stationary renewable energy storage technology, alternative membrane materials should be screened and developed to limit the high levels of electrolyte crossover. Anion exchange membranes (AEMs) could significantly lower metallic ion crossover by providing Fe2+/3+/Cr2+/3+ cation repulsion; however, recent literature has yet to show successful discharge of ICFB electrolyte when using AEMs. Base-excess membranes of various polybenzimidazole (PBI) blends were manufactured and screened to investigate the effects of membrane and electrolyte composition on the fouling phenomenon. Performance parameters of membranes were compared to the benchmark Nafion-212 CEM. Results showed elevated ionic conduction resistances from fouling and polarization of membranes in the acidic-flow battery electrolyte; however, a poly [2,2-(m-phenylene)-5,5-bibenzimidazole] (mPBI) cross-linked membrane system with 3% phosphonated poly(pentafluorostyrene) (PWN) exhibited sufficiently low resistance and enabled electrolyte cycling. While evidence suggests irreversible interactions between phosphonated ionomers and Fe/Cr cations, an mPBI-based membrane showed reduced electro-osmotic crossover rates compared to Nafion (4% vs. 33%). The positively charged PBI in acidic electrolyte increased ionic selectivity, resulting in a higher coulombic efficiency (CE of 96.7% vs. 91.8%) and a competitive energy efficiency (EE of 76.1% vs. 74.8%).

Involved external institutions

Noordwes-Universiteit / North-West University ZA South Africa (ZA) Universität Stuttgart DE Germany (DE) Forschungszentrum Jülich / Research Centre Jülich (FZJ) DE Germany (DE)

How to cite

APA:

du Toit, J.P., Atanasov, V., Cho, H., Kerres, J., Wagner, M., & Krieg, H.M. (2026). Polybenzimidazole anion-exchange membranes for the iron-chromium redox flow battery. Journal of Energy Storage, 182. https://doi.org/10.1016/j.est.2026.124419

MLA:

du Toit, J. P., et al. "Polybenzimidazole anion-exchange membranes for the iron-chromium redox flow battery." Journal of Energy Storage 182 (2026).

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