Probing buffer-driven failure modes in AEM zero-gap CO 2 electrolysis under accelerated stress conditions Aloka Kumar Sahu 1 **, Sehun Seo 1 , Francesca M. Toma 1,2,3 * 1 Institute of Functional Materials for Sustainability, Helmholtz-Zentrum Hereon, Kantstraße 55, 14513 Teltow, Germany, 2 Liquid Sunlight Alliance and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United State, 3 Faculty of Mechanical and Civil Engineering, Helmut Schmidt University, Holstenhofweg 85, 22043 Hamburg, Germany Presenteremail: **Aloka.Sahu@hereon.de *Corresponding author email: Francesca.Toma@hereon.de The long-term stability of CO 2 electrolysis systems remain a critical barrier to commercialization. 1, 2 In this study, we investigate how different alkaline buffer systems influence degradation behavior in a membrane electrode assembly (MEA) electrolyzer with an anion exchange membrane (AEM). Using a zero-gap cell with Ag gas diffusion electrode as the cathode and Ni fiber media porous transport layer as the anode, we evaluated the performance of CsHCO 3 , KHCO 3 , phosphate-buffered (KH 2 PO 4 and K 2 HPO 4 ), and mixed bicarbonate-phosphate electrolytes under accelerated stress conditions at 100-300 mA/cm 2 . Electrochemical performance was monitored over time using chronopotentiometry, EIS, and gas product analysis. Post-test diagnostics (SEM, XPS, ICP) revealed distinct buffer-dependent failure modes, phosphate buffers reduced carbonate scaling and improved pH stability but introduced surface adsorption effects, while bicarbonate systems showed higher CO selectivity but faster membrane and electrode degradation. This study identifies key electrolyte-performance trade-offs and highlights practical directions for optimizing buffer chemistry to improve AEM-based CO 2 electrolysis durability. References 1. Sassenburg, M., Kelly, M., Subramanian, S., Smith, W. A., Burdyny, T., Zero-Gap Electrochemical CO 2 Reduction Cells: Challenges and Operational Strategies for Prevention of Salt Precipitation, ACS Energy Lett. 2023 , 8, 1, 321–331. 2. Salvatore, D.A., Gabardo, C.M., Reyes, A. et al., Designing anion exchange membranes for CO 2 electrolysers, Energy 2021 , 6, 339–348.
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