Tuning the electrocatalytic activity of perovskites through active site variation and support interactions

We present a series of perovskite electrocatalysts that are highly active for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in an aqueous alkaline electrolyte. Lanthanum-based perovskites containing different transition metal active sites (LaBO₃, B = Ni, Ni _0.75Fe_0.25, Co, Mn) are synthesized by a general colloidal method, yielding phase pure catalysts of homogeneous morphology and surface area (8-14 m²/g). Each perovskite's ability to catalyze the OER and ORR is examined using thin film rotating disk electrochemistry (RDE). LaCoO ₃ supported on nitrogen-doped carbon is shown to be ∼3 times more active for the OER than high-surface-area IrO₂. Furthermore, LaCoO₃ is demonstrated to be highly bifunctional by having a lower total overpotential between the OER and ORR (δE = 1.00 V) than Pt (δE = 1.16) and Ru (δE = 1.01). The OER and ORR pathways are perturbed by the introduction of peroxide disproportionation functionality via support interactions and selective doping of the catalyst. LaNi _0.75Fe_0.25O₃'s ability to disproportionate peroxide is hypothesized to be responsible for the ∼50% improvement over LaNiO₃ in catalytic activity toward the ORR, despite similar electronic structure. These results allow us to examine the pathways for OER and ORR in context of support interactions, transition metal redox processes, and catalytic bifunctionality.