Dynamic Surface and Bulk Phase Transitions at the Oxide/Electrolyte Interface During Oxygen Evolution Reactions

Perovskite-type oxides have gained increasing interest in electrocatalytic water splitting due to their versatile elemental compositions and tunable electronic structures. Recent experimental observations show that perovskite oxide catalysts can experience dynamic changes in both surface and bulk during the oxygen evolution reaction (OER), rather than remaining static [1,2]. Moreover, the composition and/or structure may further evolve, driven by potential-induced changes in ionic defect concentration, which can impact OER activity and stability. However, elucidating the dynamic changes at the electrode solid-liquid interface and the quantitative defect-potential relationship remains a challenge. Here, with a model system of epitaxial strontium cobaltite (SrCoO_3-<i>δ</i>) thin films, we find that SrCoO_3-<i>δ</i> is rather dynamic during OER that shows a bulk phase transition via electrochemically induced oxygen intercalation, as well as a surface transformation towards Co (oxy-)hydroxide via Sr leaching. A toolkit of electrochemical-based methods has been performed to quantify the change of oxygen nonstoichiometry in SrCoO_3-<i>δ</i> as a function of potentials. We further probe the bulk and surface phase transitions including the thickness of the formed (oxy-)hydroxides layer by using operando techniques. Our findings thus provide a reliable experimental framework for investigating surface and bulk transformations in perovskite electrocatalysts and open up opportunities for shedding more insights into the OER activity and operational stability of perovskite electrocatalysts.<br/>References:<br/>[1] Lopes. P. <i>et al.</i>, J. Am. Chem. Soc. 143, 7, 2741-2750(2021).<br/>[2] Baeumer, C., Li, J., Lu, Q. <i>et al</i>., Nat. Mater. 20, 674-682 (2021).