OER catalyst stability investigation using RDE technique: A stability measure or an artifact?

The rotating disk electrode (RDE) technique was frequently used for investigating the stability of oxygen evolution reaction (OER) catalysts under galvanostatic conditions, where the increase in potential is reported to be due to catalyst degradation. The galvanostatic RDE stability test typically results in catalyst life-time of several hours, although the same catalyst can last for thousands of hours in a PEM electrolyzer under similar conditions, a discrepancy that is still unresolved. In this work, we present a careful examination of the use of the RDE technique as a tool for the investigation of the OER catalyst stability. Our findings provide a clear evidence that the change in potential during the stability test is not related at all to catalyst degradation, but is rather due to an experimental artifact caused by nano- and micro-bubbles formed within the pores of the catalyst layer during the OER, which cannot be removed by electrode rotation. Instead, they accumulate and shield the OER active sites from the electrolyte, resulting in an increase of the potential, which is mistakenly interpreted as catalyst degradation in previous literature. Thus, reliable OER catalyst stability tests other than testing in a real electrolyzer cell still needs to be designed.