Strong Activity Changes Observable during the First Pretreatment Cycles of Trimetallic PtNiMo/C Catalysts

Pt-based alloy catalysts supported on carbon are commonly characterized for oxygen reduction reaction (ORR) activity using the rotating disk electrode technique (RDE). Within this study, we show exemplarily for PtNiMo/C catalysts that the applied pretreatment influences strongly the determined activity. The classically employed descriptor of unchanged cyclic voltammetry response is insufficient to portrait completed surface restructuring, and gives an incorrect impression that stable activity can be determined. This might be one of the reasons for the strongly deviating activities reported in literature. Following the changes in activity during pretreatment also with in-situ FTIR and online dissolution measurements gives insights to an up to now largely overseen high activity of the trimetallic catalysts. A maximum activity of 0.57 mA cm_Pt⁻² at 0.95 V_RHE is reached quickly during the first six cycles and decreases slowly subsequently. The maximum activity and change of activity over the cycle number is affected by the scan rate and electrolyte refreshing, while the gas atmosphere plays only a minor role. This exemplary study might be important for Pt alloy catalysts in general.