Contribution of the Sub‐Surface to Electrocatalytic Activity in Atomically Precise La_0.7Sr_0.3MnO₃ Heterostructures

Abstract Electrocatalytic reactions are known to take place at the catalyst/electrolyte interface. Whereas recent studies of size‐dependent activity in nanoparticles and thickness‐dependent activity of thin films imply that the sub‐surface layers of a catalyst can contribute to the catalytic activity as well, most of these studies consider actual modification of the surfaces. In this study, the role of catalytically active sub‐surface layers was investigated by employing atomic‐scale thickness control of the La_0.7Sr_0.3MnO₃ (LSMO) films and heterostructures, without altering the catalyst/electrolyte interface. The activity toward the oxygen evolution reaction (OER) shows a non‐monotonic thickness dependence in the LSMO films and a continuous screening effect in LSMO/SrRuO₃ heterostructures. The observation leads to the definition of an “electrochemically‐relevant depth” on the order of 10 unit cells. This study on the electrocatalytic activity of epitaxial heterostructures provides new insight in designing efficient electrocatalytic nanomaterials and core‐shell architectures.