Atomic layer deposition based surface modification on perovskite oxide air electrodes

Perovskite oxides such as Sr2Fe1.5Mo0.5O6-δ (SFMO) offer excellent performance as solid oxide cell (SOC) electrodes, but their durability is severely limited by surface segregation of the A-site cation (Sr²⁺). This degradation is driven by lattice strain from cation size mismatch and by the accumulation of oxygen vacancies at the surface. Conventional mitigation strategies, such as cation doping to reduce surface oxygen vacancies or inert oxide coatings, suppress Sr segregation but inevitably sacrifice electrochemical activity. This dissertation demonstrates that this dilemma can be fundamentally reshaped through atomically engineered surface modifications achieved via atomic layer deposition (ALD). Three complementary approaches are developed and systematically compared. First, non-stoichiometric ZrOx coatings deposited by ALD simultaneously suppress Sr segregation and preserve excellent oxygen surface exchange kinetics. Second, nitrogen trapped within TiOx films stabilizes non-stoichiometric structures, enhancing oxygen exchange kinetics at elevated temperatures while suppressing Sr enrichment, revealing defect-imprinting as an independent and tunable handle for promoting ORR/OER reactivity. Third, an air-compatible Ir-Fe exsolution mechanism is established by exploiting the intrinsic miscibility between Ir and Fe. ALD-derived Ir clusters selectively extract Fe from the lattice during annealing in air, forming socketed Ir-Fe nanoalloys without a reducing atmosphere. These anchored nanoalloys resist coarsening, moderate local lattice strain, and suppress Sr migration pathways, enabling catalytic enhancement under oxidizing conditions. Across these strategies, the dissertation integrates transmission electron microscopy (TEM), X-ray based spectroscopy (XPS, XRD, and XAS), and electrochemical analysis to resolve how engineered surfaces via ALD migrate Sr segregation, activity improvement, and long-term durability at high temperature (800 ˚C). The results demonstrate that neither stability nor activity is an immutable property of the pristine perovskite surface; instead, both can be deliberately tuned through targeted surface chemistry, vacancy stabilization, and catalytic phase formation. Taken together, this work provides a design framework for perovskite SOC air electrodes, showing that atomic-scale surface engineering can reconcile the traditional stability-activity trade-off and open new pathways for durable, high-performance solid oxide electrochemical devices.