The Power of Reference Electrodes in AEM Electrolysis

Abstract

The use of reference electrodes is a powerful diagnostic tool to determine the overpotentials associated with oxygen and hydrogen evolution reaction. Yet, the use of reference electrodes in flow cells is still uncommon and provides several challenges especially related to the stability of the potential of the reference electrode. This study investigates the use of a reference electrode in a well-performing iridium-free AEM flow cell with a cell potential of <1.8 V @ 1.5 A cm-2. The reference electrode consists of electrically insulating foil with two platinum wire electrodes on one side as shown in Figure 1(left). A small micro-current is passed through the platinum wires to maintain hydrogen coverage on the reference electrode to establish equilibrium cell potential. The use of the reference electrode shows that the platinum-ruthenium cathode performs particularly well with an overpotential of <0.1 V @ 0.2 A cm-2.The reference electrode also is useful for the study of cell degradation. One of the major challenges of coupling electrolyzer directly to renewables are reverse currents flowing after shutdown in alkaline and AEM electrolyzers [1]. In this study, polarities were reversed to simulate these reverse currents. This lead to a significant increase in cell potential. It is clearly evident from Figure 1(right) that the cathode overpotentials increased significantly after this reverse current application, thereby indicating that the platinum-ruthenium cathode is vulnerable to reverse currents.[1]Ashraf Haleem et al, Effects of operation and shutdown parameters and electrode materials on the reverse current phenomenon in alkaline water analyzers, Journal of Power Sources, Volume 535, 2022, 231454, ISSN 0378-7753, https://doi.org/10.1016/j.jpowsour.2022.231454 Figure 1