Investigation of Water Dissociation Catalyst Layer Configurations for Bipolar Membrane Water Electrolzyers
Authors: Gado Alanna M. , Bliznakov Stoyan , Bonville Leonard J. , Maric Radenka 
Published: December 2024

Water electrolysis is a promising technology for the production of sustainable green hydrogen. Alkaline exchange membrane water electrolyzers (AEMWEs) operate at low current densities (<1.0 Acm-2) and low pressures (<30 bars), and have very long operating lifetimes (over 100,000 h) [1]. On the other hand, proton exchange membrane water electrolyzers (PEMWEs) are able to operate at high current densities (>2.0 Acm-2) and pressures (>300 bars), but rely on expensive platinum group metal (PGM) catalysts (Pt, Ir) with a shorter lifetime (80,000 h, 2026 DoE target) [1, 2]. In order to bridge this gap, a newer, under-investigated configuration may have significant advantages: bipolar membranes.

Bipolar membranes (BPMs) for water electrolysis consist of two membrane layers: a cation exchange layer (CEL) and anion exchange layer (AEL). This allows the electrolyzer to operate with a high pH gradient with an acidic cathode and basic anode (reverse bias) [3]. Operation in reverse bias mode allows for optimal pH conditions for the half-cell reaction kinetics for a BPM electrolyzer. The BPM aims to maximize OH-
and H+
transport, promoting kinetically favorable conditions.

BPMs face significant challenges with respect to both performance and durability. BPMs have demonstrated low operational current density compared to PEMWEs [4-6]. Traditional BPMs experienced catalyst layer delamination, failure due to “ballooning”, and significant ohmic resistance, all of which drastically limit cell performance and durability. One method for mitigating all three failure modes is the inclusion of a water dissociation (WD) catalyst at the interlayer. The WD interlayer can mitigate water buildup at the CEL—AEL interface, and can reduce the ionic resistance between the two dissimilar layers. It is vitally important to have a mechanically stable membrane configuration while achieving high performance. BPMs without a well-designed ionomer junction cannot operate effectively without the inclusion of a catalyst at the interlayer junction [7].

In this work, reactive spray deposition technology (RSDT) was used to fabricate low loaded, high electrochemically active surface area (ECSA) catalysts as WD interlayers for BPMs. Polarization, electrochemical impedance spectroscopy, and distribution of relaxation times are used to investigate cell performance and short-term durability.

References

[1] Q. Feng, G. Liu, B. Wei, Z. Zhang, H. Li, H. Wang, et al., “A review of proton exchange membrane water electrolysis on degradation mechanisms and mitigation strategies,” Journal of Power Sources, vol. 366, pp. 33–55, 2017.

[2] Hydrogen and F. C. T. Office, “Technical targets for proton exchange membrane electrolysis.”

[3] M. A. Blommaert, D. Aili, R. A. Tufa, Q. Li, W. A. Smith, and D. A. Vermaas, “Insights and challenges for applying bipolar membranes in advanced electrochemical energy systems,” ACS Energy Letters, vol. 6, no. 7, pp. 2539–2548, 2021.

[4] J. A. Wrubel, Y. Chen, Z. Ma, and T. G. Deutsch, “Modeling water electrolysis in bipolar membranes,” Journal of The Electrochemical Society, vol. 167, no. 11, p. 114502, 2020.

[5] S. Z. Oener, M. J. Foster, and S. W. Boettcher, “Accelerating water dissociation in bipolar membranes and for electrocatalysis,” Science, vol. 369, no. 6507, pp. 1099–1103, 2020.

[6] O. Weiland, P. Trinke, B. Bensmann, and R. Hanke-Rauschenbach, “Modelling water transport limitations and ionic voltage losses in bipolar membrane water electrolysis,” Journal of The Electrochemical Society, vol. 170, no. 5, p. 054505, 2023.

[7] C. Shen, R. Wycisk, and P. N. Pintauro, “High performance electrospun bipolar membrane with a 3d junction,” Energy & Environmental Science, vol. 10, no. 6, pp. 1435– 1442, 2017.