In Situ Measurement of Oxygen Vacancy Dynamics and Surface Exchange Reactions in Oxide Electrode under Solid Electrochemical Cell Operating Conditions

ABSTRACT Solid oxide electrochemical cells (SOCs) employ mixed ionic–electronic conducting (MIEC) perovskite electrodes, where electrochemical performance is dictated by the oxygen surface exchange coefficient ( k ) and the concentration of oxygen vacancies (δ). Conventional methods evaluate k and δ separately and under conditions that do not reflect their coupled behavior during operation, offering only a partial picture of the underlying processes. Here we report an in situ methodology that simultaneously resolves k and δ under realistic SOC operating conditions, using a dense bulk electrode integrated with a solid electrolyte. An applied overpotential induces an abrupt drop in the oxygen chemical potential gradient, enabling direct analysis of defect chemistry and surface reaction kinetics. The extracted values are consistent with those obtained from established characterization methods, validating the accuracy of the approach. Beyond fundamental characterization, the platform captures dynamic evolutions in defect chemistry and reaction kinetics, providing mechanistic insights into electrode degradation.