Enhanced OER Performance and Dynamic Transition of Surface Reconstruction in LaNiO 3 Thin Films with Nanoparticles Decoration

In an electrocatalytic process, the cognition of the active phase in a catalyst has been regarded as one of the most vital issues, which not only boosts the fundamental understanding of the reaction procedure but also guides the engineering and design for further promising catalysts. Here, based on the oxygen evolution reaction (OER), the stepwise evolution of the dominant active phase is demonstrated in the LaNiO 3 (LNO) catalyst once the single‐crystal thin film is decorated by LNO nanoparticles. It is found that the OER performance can be dramatically improved by this decoration, and the catalytic current density at 1.65 V can be enhanced by ≈1000% via ≈10 9 cm −2 nanoparticle adhesion after extracting the contribution of surface enlargement. Most importantly, a transition of the active phase from LNO to NiOOH via surface reconstruction with the density of LNO nanoparticles is demonstrated. Several mechanisms in terms of this active phase transition are discussed involving lattice orientation‐induced change of the surface energy profile, the lattice oxygen participation, and the A/B‐site ions leaching during OER cycles. This study suggests that the active phases in transition metal‐based OER catalysts can transform with morphology, which should be corresponding to distinct engineering strategies.