Built-In Open Circuit Reference Electrodes in a PEM Water Electrolysis Cell – A Proof of Concept

This study presents a proof of concept for the integration of open circuit reference electrodes (OC-REs) in proton-exchange membrane water electrolysis (PEMWE) cells to understand electrode performance and loss mechanisms, allowing for unequivocal assignment of these losses to anode and cathode. OC-REs, which are non-invasive to cell performance and share the same environment as the working electrodes (WEs), are assessed for stability and reproducibility while their performance is investigated across varying current densities and membrane thicknesses. Results demonstrate the significant impact of hydrogen crossover on the potential of the anode RE, impact that was modeled by calculating a current-density-dependent mixed potential. When comparing half-cell and full-cell polarization, the latter shows significantly higher reproducibility, with proper electrode alignment being crucial to minimize differences in half-cell polarization curves. Conversely, no significant impact from alignment on half-cell electrochemical impedance spectroscopy (EIS) was observed, making this technique the more consistent approach. The half-cell EIS revealed a significant contribution from the cathode to the overall loss, contrary to indications from most studies lacking this half-cell insight. These findings illustrate the potential of OC-REs as effective sensors for assessing electrode contributions, paving the way for future investigations into optimizing PEMWE.