Disentangling the Pitfalls of Rotating Disk Electrode-Based OER Stability Assessment: Bubble Blockage or Substrate Passivation?

Oxygen evolution reaction (OER) catalyst stability metrics derived from aqueous model systems (AMSs) prove valuable only if they are transferable to technical membrane electrode assembly (MEA) settings. Currently, there is consensus that stability data derived from ubiquitous rotating disk electrode (RDE)-based investigations substantially overestimate material degradation mainly due to the nonideal inertness of catalyst-backing electrode materials as well as bubble shielding of the catalyst by evolved oxygen. Despite the independently developed understanding of these two processes, their interplay and relative impact on intrinsic and operational material stability have not yet been established. Herein, we employ an inverted RDE-based approach coupled with online gas chromatographic quantification that exploits buoyancy and anode hydrophilicity existing under operating acidic OER conditions and excludes the influence of bubble retention on the surface of the catalyst. This approach thus allows us to dissect the degradation process occurring during the RDE-based OER stability studies. We demonstrate that the stability discrepancy between galvanostatic nanoparticle (NP)-based RDE and MEA data does not originate from the accumulation of bubbles in the catalyst layer during water oxidation but from the utilization of corrosion-prone substrate materials in the AMS. Moreover, we provide mechanistic insights into the degradation process and devise experimental measures to mitigate or circumvent RDE-related limitations when the technique is to be applied to an OER catalyst stability assessment. These findings should facilitate the transferability between AMS and MEA approaches and promote further development of the latter.