Reference-Electrode Configuration in CO2 Electrolysis (CO2E) and Anion-Exchange Membrane Water Electrolysis (AEMWE) Cells for Degradation and Stability Evaluation

CO 2 electrolysis (CO2E) and anion-exchange membrane water electrolysis (AEMWE) have both been identified as promising technologies for reducing emissions from the industrial and energy sectors in pursuit of achieving net-zero goals. 1,2,3,4 Recent developments of electrocatalysts, membranes, and electrolyser cell design have resulted in rapid progress of CO2E and AEMWE, achieving high current densities and faradaic efficiencies at the laboratory scale. 1,2 However, the long-term stability of these technologies requires improvement if they are to be deployed at commercially relevant scales. 2,5 Unfortunately, degradation phenomena such as; cathode flooding 6, 10 , catalyst degradation 7 , membrane instability 8,9 , and salt precipitation 10 are difficult to diagnose electrochemically, without the ability to decouple resistance contributions in-situ .We have therefore developed a 3-electrode technique and explored protocols that allow for the decoupling of cathode and anode overpotentials during long-term stability measurements. By using an edge-type reference electrode connected to the membrane through a liquid electrolyte bridge, we successfully demonstrate the ability to assess the performance of individual components within different membrane-electrode assembly (MEA) configurations. We highlight instabilities with using edge-type reference electrodes such as changes in the pH of the electrolyte bridge, and discuss efforts to mitigate these issues to permit long-term stability testing. We then demonstrate how this method can be used to provide more insights into degradation phenomena in both CO 2 and AEM water electrolyser cells, showing early diagnosis - up to 7 hours before detection from a conventional 2-electrode set-up - of failure mechanisms during stability testing. The proposed 3-electrode technique is capable of separating anode and cathode overpotentials over the course of extended testing periods and provides a platform to study the electrochemical response of individual electrolyser components to various degradation phenomena, and the durability of CO2E and AEMWE materials. Critical gaps in knowledge surrounding these issues can be better understood, which will enable these technologies to advance to the next stages of development. References: Li, Q., Molina Villarino, A., Peltier, C. R., Macbeth, A. J., Yang, Y., Kim, M. J., Shi, Z., Krumov, M. R., Lei, C., Rodríguez-Calero, G. G., Soto, J., Yu, S., Mutolo, P.F., Xiao, L., Zhuang, L., Muller, D. A., Coates, G.W., Zelenay, P., & Abruna, H. D. (2023). Anion Exchange Membrane Water Electrolysis: The Future of Green Hydrogen. The Journal of Physical Chemistry C , 127 (17), 7901-7912. Lin, J., Zhang, Y., Xu, P., & Chen, L. (2023). CO2 electrolysis: Advances and challenges in electrocatalyst engineering and reactor design. Materials Reports: Energy , 100194. Al‐Mamoori, A., Krishnamurthy, A., Rownaghi, A. A., & Rezaei, F. (2017). Carbon capture and utilization update. Energy Technology , 5 (6), 834-849. Baena-Moreno, F. M., Rodríguez-Galán, M., Vega, F., Alonso-Fariñas, B., Vilches Arenas, L. F., & Navarrete, B. (2019). Carbon capture and utilization technologies: a literature review and recent advances. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects , 41 (12), 1403-1433. Li, D., Motz, A. R., Bae, C., Fujimoto, C., Yang, G., Zhang, F. Y., Ayers, K. E., & Kim, Y. S. (2021). Durability of anion exchange membrane water electrolyzers. Energy & Environmental Science , 14 (6), 3393-3419. Warkentin, H., O'Brien, C. P., Holowka, S., Maxwell, B., Awara, M., Bouman, M., Zeraati, A. Z., Nicholas, R., Ip, A. H., Elsahwi, E. S., Gabardo, C. M., & Sinton, D. (2023). Early Warning for the Electrolyzer: Monitoring CO2 Reduction via In‐Line Electrochemical Impedance Spectroscopy. ChemSusChem , e202300657. Mardle, P., Chen, B., & Holdcroft, S. (2023). Opportunities of Ionomer Development for Anion-Exchange Membrane Water Electrolysis: Focus Review. ACS Energy Letters , 8 (8), 3330-3342. Alkayyali, T., Zeraati, A. Z., Mar, H., Arabyarmohammadi, F., Saber, S., Miao, R. K., O’Brien, C., Liu, H., Xie, Z., Wang, G., Sargent, E. H., Zhao, N., & Sinton, D. (2023). Direct Membrane Deposition for CO 2 . ACS Energy Letters , 8, 4674-4683 Mardle, P., Gangrade, A., Saatkamp, T., Jiang, Z., Cassegrain, S., Zhao, N., Shi, Z., & Holdcroft, S. (2023). Performance and Stability of Aemion and Aemion+ Membranes in Zero‐Gap CO2 Electrolyzers with Mild Anolyte Solutions. ChemSusChem , 16 (14), e202202376. Mardle, P., Cassegrain, S., Habibzadeh, F., Shi, Z., & Holdcroft, S. (2021). Carbonate ion crossover in zero-gap, KOH anolyte CO2 electrolysis. The Journal of Physical Chemistry C , 125 (46), 25446-25454. Figure 1