Guidance for targeted degradation analysis of OER kinetics of low-loading iridium-based catalysts in PEM water electrolysis cells

This paper critically evaluates three methods for determining metrics of the oxygen evolution reaction (OER) describing the performance and stability of low-loading iridium-based anode catalyst layers (CLs) in proton exchange membrane water electrolysis (PEMWE) cells. The methods applied are OER mass activity, voltage breakdown analysis (VBA), and constant Tafel slope VBA (CT-VBA). They are used to assess the OER metrics as a function of anode CL configurations, potential cycling, and level of degradation. Therefore, various accelerated stress tests (ASTs) are carried out for a targeted degradation of different anode CLs based on Ir black or Ir oxide. It turns out that the OER mass activity method is robust, straightforward and an ideal method for e.g., in-house screening tasks. On the other hand, the VBA method is suitable for comparative analysis across laboratories by distinguishing between the three main overpotentials. The CT-VBA method, however, offers improved accuracy, as it accounts for mass transport overpotential at low current density, and is particularly suitable for determining apparent exchange current density values further used in modelling approaches. This benefit comes with a drawback, as commonly accepted reference Tafel slopes for respective catalyst type and PTL configurations would be required within the PEMWE community. This guidance therefore helps to choose the right method for determining OER metrics depending on the research question.