Uncovering Heterogeneous Energetic Trajectories in NiFe Oxygen Evolution Electrocatalysis through Integrated Raman, Electrochemical and Microkinetic Analysis

Fe incorporation strongly modifies the activity of Ni-based electrocatalysts, but how heterogeneous surface states contribute to this behavior remain unclear due to improper understanding about intermediate evolution. Here, we investigate whether correlations between spatially resolved spectroscopic features and electrochemical responses can reveal distinct energetic and kinetic characteristics of NiFe electrodes. We combine in-situ Raman mapping, electrochemistry and microkinetic modeling to study three NiFe electrodes prepared under different Fe-deposition conditions. Potential-dependent spectra reveal site-to-site variations in NiOOH related vibrational features and higher-wavenumber oxygen-associated spectral signatures across individual surface sites. Correlation and regression analyses identify a compact set of Raman descriptors associated with the electrochemical response, while sitespecific predicted scores reveal distinct potential-dependent trajectory patterns. Raman-guided projection into a model-derived intermediate-energy space further enables comparison of these trajectory phenotypes within a common thermodynamic framework. Although the projected energetic distributions exhibit substantial overlap, their arrangement and model-estimated kinetic characteristics vary across different trajectory phenotypes and kinetic regimes. These findings suggest that spatially heterogeneous NiFe surface states may exhibit different kinetic responses under applied potential, instead of following a uniform catalytic evolution. More broadly, this study demonstrates the potential of integrating independent spectroscopic and electrochemical observations with microkinetic modelling to uncover energetic and kinetic heterogeneity in OER electrocatalysis.