Onset of Surface Modifications on Perovskite Oxide Catalysts under Oxygen Evolution Reaction Conditions Revealed by Electrochemical Friction Force Microscopy

Identifying the onset potential at which perovskite oxide catalysts begin to undergo near-surface changes under oxygen evolution (OER) polarization is critical for separating intrinsic electrocatalytic behavior from evolving surface chemistries. Here, early surface modification was tracked during the first anodic sweep in 0.1 M KOH using electrochemical friction force microscopy (EC-FFM) under a low normal load of 5 nN to avoid mechanically induced removal of the reacted layer. Epitaxial La0.6Sr0.4BO3–δ thin films (B = Co or Fe) were probed while recording cyclic voltammograms (CV). Onset potentials were extracted from friction (EF), topographic roughening (ER), and the CV current response (Ej) using a consistent tangent method. For both catalysts, friction changes preceded morphology changes, with EF occurring 0.26 ± 0.02 V earlier than ER for LSCO and 0.13 ± 0.05 V earlier than ER for LSFO (all potentials vs. RHE) at 10 mV s–1. Based on the established involvement of OH-derived surface species in alkaline OER mechanisms and the demonstrated sensitivity of electrochemical friction to adsorbate-induced changes of the interface, EF is assigned to the onset of a friction-detectable interfacial modification that is consistent with potential-induced hydroxide adsorption/surface hydroxylation, whereas ER marks the onset of morphologically resolvable surface restructuring. The material-dependent ΔE = ER – EF separation therefore describes the potential interval between the initial friction-detectable interfacial modification and its morphological expression.