Aerobic Dehydrogenation by Coupled Electrochemical Reactions Governs Room-Temperature Proton Defect Chemistry in Functional Oxides

Abstract Tuning functional oxides by controlling ionic point defects is a well-established paradigm for designing tailored functionalities. At elevated temperatures, this is usually achieved by tuning ambient oxygen partial pressure (pO2) to regulate oxygen chemical potential and defect (e.g., protons and oxygen vacancies) concentrations. At room temperature, however, atmosphere-driven tuning is considered unfeasible due to sluggish surface kinetics and negligible ionic mobility. Here, using hydrogenated NdNiO3 as a model system, we show that ambient pO2 can in fact regulate hydrogen chemical potential and protonic defects through aerobic dehydrogenation driven by coupled anodic proton extraction and cathodic oxygen reduction in aqueous solutions. Using mixed-potential theory together with operando electrochemical, optical, and structural characterizations, we quantitatively analyze these coupled half-reactions and determine how pO2 modulates dehydrogenation kinetics. These insights deepen the understanding of room-temperature defect chemistry and provide guidance for designing functional oxide devices based on controlled modulation of ionic defects.