<b>Adsorbed Oxygen Dynamics at Forced Convection Interface in the Oxygen Evolution Reaction</b>

The oxygen evolution reaction (OER) is a prevalent anodic reaction in electrocatalytic processes. Modulation of adsorbed oxygen (*O) at the electrochemical interface is an effective means to reduce the OER overpotential. However, the contribution of various *O conversions to the overpotential remains unclear. Herein, the development of a multi-component forced convection electrochemical mass spectrometry constructs *O-labeled electrochemical interfaces with specific coverages to track the *O conversions. The relationships between the Faradic contributions and the specific *O conversion pathways are established by considering the anomalous fractionation of O2. Our experiments confirm that *O coupling contributes up to 48% with a specific overpotential on full coverage Pt. Distinguishing the *O conversion contributions with various coverages reveals that balancing the *O formation and conversions, especially *O coupling enables further minimization of the OER overpotential. Thus, tracking the intermediate conversions has significant implications for designing high-performance electrocatalytic interfaces.