Trace Fe in alkaline electrolyte governs the OER activity of perovskite LaNiO3 and La2NiO4 via interaction with redox-active surface NiOxHy formed by applied bias.

Accurate description of activity trends among perovskite oxide oxygen evolution catalysts using electronic descriptors requires that the bulk structure of the catalyst is comparable to that of the surface. Few studies have thus far addressed the dynamic nature of the catalyst’s structure during the oxygen evolution reaction (OER) and the consequential implications for rationalization of activity. Here, we use a combination of electrochemical and materials characterization techniques to show the surface reconstruction of LaNiO3 particles, LaNiO3 epitaxial films, and an analogous Ruddlesden-Popper phase, La2NiO4. Small, but characteristic redox features corresponding to Ni redox in amorphous NiOxHy are observed during cyclic voltammetry of these nominally crystalline materials. The size of these redox features grows with prolonged cycling and contributes to an increased surface area as determined from electrochemical impedance spectroscopy (EIS). These observations are consistent with the reconstruction of the crystalline surface into NiOxHy and subsequent activation by adsorption of Fe forming the well-known and extremely active NiFeOxHy OER catalyst.