Solid oxide fuel cells (SOFCs) provide fuel flexibility and the highest efficiency of any chemical-to-electrical energy conversion technology. Unfortunately, slow oxygen transport, especially that caused by low surface exchange kinetics at the cathode, limits overall SOFC performance. In the common SOFC material La0.6Sr0.4FeO3-delta (LSF64) efforts to engineer and understand oxygen surface exchange have been complicated by the 5 orders of magnitude chemical surface exchange coefficient (k) discrepancy reported in the literature. To help remedy this discrepancy, a new bilayer curvature relaxation technique utilizing the mechano-chemical coupling of LSF64 was developed in this work. This technique provides reliable, in-situ, electrode-free, simultaneous measurement of film stress and k as a function of temperature and oxygen partial pressure. This is demonstrated here by measuring LSF64 films prepared via sputter deposition, pulsed laser deposition, and colloidal spray deposition. The similarities and differences between these films are systematically investigated across multiple thermal cycles, and correlated to the microstructure, stress state and sample preparation/testing history. Further, the k of LSF64 films was measured here below 500oC for the first time, and distinct lattice-dominated and grain-boundary-dominated chemical stress responses were identified.
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