(Energy Technology Division Graduate Student Award sponsored by BioLogic) In-Situ Diagnostic Tools and Analysis to Identify Root Causes for Voltage Losses in Anion Exchange Membrane Water Electrolyzers

Water electrolysis has been getting significant attention worldwide as a leading technology that allows for the storage of renewable energy in the form of hydrogen. Anion exchange membrane water electrolyzers (AEMWEs) have emerged in recent years as a possible low-cost and high performance alternative to traditional alkaline electrolyzers (AWEs) and proton exchange membrane electrolyzers (PEMWEs). AEMWEs can potentially offer the complimentary benefits of the two developed technologies, namely high current density, pressurized cell operation, the use of platinum group metal (PGM) free electrocatalysts, and the ability to use earth abundant cheap materials for other cell components 1-2 . AEMWEs are currently in an early research and development stage. Most of the attention has been focused on the development of new polymers, electrocatalysts and other component materials 3-4 . Such materials are generally reported to offer high performance and durability, evaluated using standard ex-situ electrochemical techniques. Integration of these materials in actual water electrolyzer system often does not translate linearly into long life and high performance, and understanding material behavior in the real operating conditions is essential for their large-scale deployment. In-situ performance evaluation and diagnostic tools help analyze the contributions from individual components at membrane electrode assembly (MEA) level 5-7 . Differentiating kinetic, ohmic, transport as well as the catalyst layer overpotential contributions may lead a way for enhancing overall device performance and degradation. For instance, high IEC, water uptake and conductivity of polymer membranes and ionomers are desirable, however, may not linearly translate in high in-situ performance. Excessive swelling of the membrane and/or ionomer may dominate, increasing the charge transfer resistance, subsequently lowering the overall device performance 8 . In this presentation, a combination of methods – electrochemical impedance spectroscopy (EIS), cyclic voltammograms (CVs), I-V scans and constant current / voltage hold – are used to evaluate device performance and separate individual voltage losses caused by each MEA component. These tools help pinpoint the shortcomings of individual components that lead to losses in cell performance or degradation, allowing for new control strategies to be developed. References: 1. K. E. Ayers, E. B. Anderson, C. B. Capuano, M. Niedzwiecki, M. A. Hickner, C. Y. Wang, Y. Leng and W. Zhao, ECS Trans., 121 (2013). 2 . M. Götz, J. Lefebvre, F. Mörs, A. M. Koch, F. Graf, S. Bajohr, R. Reimert, T. Kolb, Renewable Energy, 1371 (2016). 3. N.U. Hassan, E. Motyka, J. Kweder, P. Ganesan, B. Brechin, B. Zulevi, H. R.C. Mercado, P. A. Kohl, and W. E. Mustain , J. Power Sources , 232371 (2023). 4 . N.U. Hassan, M. Mandal, B. Zulevi, P. A. Kohl and W. E. Mustain, Electrochim. Acta , 409, 140001 (2021). 5. J. Liu, Z. Kang, D. Li, M. Pak, S.M. Alia, C. Fujimoto, G. Bender, Y.S. Kim and A.Z. Weber, J. Electrochem. Soc. , 168 054522 (2021). 6. I. Vincent, E. C. Lee & H. M. Kim, Scientific Reports , 80683-6 (2021). 7 . N.U. Hassan, Y. Zheng, P.A. Kohl and W.E. Mustain, J. Electrochem. Soc ., 044526 (2022). 8. G. Huang, M. Mandal, N.U. Hassan, K. Groenhout, A. Dobbs, W. E. Mustain and P. A. Kohl, The J. Electrochem. Soc., 164514 (2020). Figure 1