In-Operando Friction Force Microscopy Reveals Degradation and Repassivation of Epitaxial Perovskites During Oxygen Evolution Reaction Under Dynamic Cycling Conditions

A detailed understanding of catalyst degradation under dynamic conditions is essential to develop improved catalysts for the oxygen evolution reaction (OER), the bottleneck for efficient electrochemical water splitting in alkaline media. Perovskite oxides represent an interesting class of OER electrocatalysts, however, the differences in their degradation and repassivation growth rate are not yet fully understood. To address this, epitaxially grown La_0.6Sr_0.4CoO₃ (LSCO), La_0.6Sr_0.4FeO₃ (LSFO), and La_0.6Sr_0.4MnO₃ (LSMO) have been analyzed by in-operando friction force microscopy (FFM) during cyclic voltammetry in 0.1 M KOH. Distinctly different degradation phenomena for these materials were found. Continuous topography and friction force measurements during cycling, and postcatalysis characterization, clearly demonstrated the irreversibility of the degradation process, under dynamic conditions. Specifically, LSMO develops a robust passivation layer accompanied by pronounced roughening. LSFO forms a thin, surface-limited passivating layer with better retention, and LSCO undergoes rapid near-surface conversion with a comparatively soft adlayer. It is demonstrated that the load on the tip has a strong influence on the obtained results, which is used for an attempt to calculate the repassivation rate of the different adlayers. The results elucidate how in-operando FFM can differentiate degradation mechanisms under reaction conditions in alkaline environments and between transition metals in perovskite oxides.