Decoupling Dissolution from Water Oxidation at Single-Faceted High-Entropy Perovskite Electrodes

High-entropy oxides (HEOs) are promising anode materials for the oxygen evolution reaction (OER) due to their wide compositional space and electronic flexibility. However, their electrochemical dissolution and OER remain concurrent, preventing decoupled analysis of dissolution kinetics and stability. Here, we present a combined atomic force microscopy (AFM) and scanning electrochemical cell microscopy (SECCM) strategy to decouple lattice dissolution from water oxidation under well-defined reaction conditions. Structurally analogous, atomically flat, single-faceted (001) ABO3 perovskite electrodes, La1-xSrx(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 with x = 0 and 0.3, serve as model systems to probe dissolution and OER kinetics in acid. Pipet-probed localized cyclic voltammetry and chronoamperometry reveal that the measured current contains contributions from both OER and lattice dissolution, the latter producing nanoscale dissolution pits beneath the SECCM droplet. By correlating pit-growth kinetics with total OER charge as a function of pulse duration (τ), overpotential (η), and pH, we quantitatively separate dissolution from OER. The proportional scaling between dissolution charge and total charge indicates that OER and dissolution proceed within a common kinetic regime, sharing a common intermediate. A rate-law-based analysis yields the standard dissolution rate constant (kd0 cm/s), transfer coefficient (α), and proton reaction order (b) for the dissolution of the 001 facet of both HEO-P. Our results unravel how aliovalent A-site substitution (30% Sr2+) alters dissolution kinetics, charge partitioning between dissolution and OER, and thickness-dependent stability, thereby enabling quantitative disentangling of the intrinsic activity and stability of HEO electrodes.