Probing the Intrinsic Oxygen Evolution Kinetics at Single CoFe ₂ O ₄ Nano‐Catalysts

Abstract Accurately evaluating the intrinsic oxygen evolution activity of transition metal‐based nano‐catalysts is the key for the rational design of promising energy conversion technologies including water electrolysers. Conventional ensemble measurements obscure the intrinsic activity of the used nanomaterial with binders, conductive additives, and particle–particle interactions. Herein, we combine catalytic nano‐impact electrochemistry with controlled immobilization strategies to dissect oxygen evolution reaction (OER) kinetics of CoFe 2 O 4 spinel nanoparticles in alkaline solutions across three length scales: freely diffusing single entities, adsorbed particles, and densely drop‑cast ensembles. The nano‐impact method yields discrete current transients whose amplitudes exhibit a sigmoidal potential dependence. Benefiting from the steady‐state behavior observed in the nano‐impact results, mass‐transport contributions were readily subtracted, allowing the Tafel slope to be evaluated more precisely than in ensemble measurements. The similarity in the OER Tafel slope (≈60 mV dec −1 ) between the single‐particle and the ensemble suggests that they share the same rate‑determining chemical step. The agreement between single‑entity and ensemble kinetics validates nano‐impact electrochemistry as a generic, binder‑free platform for establishing structure–activity correlations in earth‑abundant OER catalysts. These insights will accelerate the design of durable, high‑performance electrodes for renewable energy conversion.