Ion‐Coupled Redox and Nanoscale Heterogeneity in Oxygen Electrocatalysis Revealed by Correlative Operando Microscopy

Understanding how nanoscale structure, redox chemistry, and electrolyte coupling govern macroscopic electrocatalytic activity remains one of the central challenges in electrochemistry. In this talk, I will present a multiscale framework that integrates single-entity electrochemical measurements, operando spectro-microscopy, and microkinetic/DFT modeling to bridge nanoscale processes to ensemble reactivity in oxygen electrocatalysis. Using well-defined β-Co(OH) 2 platelet nanoparticles, we combine nanoscale and sub-particle Scanning Electrochemical Cell Microscopy (SECCM) with correlative operando scanning probe and X-ray microscopies to show that OER activity is confined to edge sites and is directly controlled by spatially heterogeneous ion-insertion redox chemistry. We further introduce operando TEY-STXM, a new technique enabling ~3 nm surface sensitivity with ~50 nm lateral resolution, which reveals the evolution of surface Co oxidation states and directly links surface Co 3+ to catalytic turnover under working conditions. To generalize these insights beyond cobalt hydroxides, we combine computational thermodynamic and kinetic modeling to rationalize how pH-dependent electric fields and cation (de)insertion reshape scaling relations and enable bifunctional oxygen evolution/reduction activity in MnO 2 . This mechanistic picture is further supported by our coupled DFT-microkinetic modeling methodology for interpreting full Tafel behavior in multi-electron reactions, which captures kinetically controlled surface coverage effects on electrocatalytic processes. Together, these results illustrate how nanoscale heterogeneity, interfacial ion dynamics, and electrolyte-dependent energetics collectively determine macroscopic catalytic performance. The combined experimental-theoretical approach offers a roadmap to design next-generation oxygen-electrode materials with tunable activity and selectivity.