Freestanding large-area epitaxial oxide nanocomposites transferred into functional electrochemical devices

Freestanding complex oxide thin films offer a promising route to decouple growth optimization from device integration, while providing direct access to buried interfaces and local structural and chemical heterogeneities. Here, we extend a sacrificial-layer-assisted transfer strategy to vertically aligned nanocomposites (VANs), using epitaxial LSM-SDC (La0.8Sr0.2MnO3 – Ce0.8Sm0.2O2) as a model system. Highly ordered, square-centimeter-scale VAN films grown on optimized templates are released and transferred onto patterned single-crystal yttria-stabilized zirconia electrolytes, enabling their integration into functional electrochemical devices. The transferred membranes retain their dense, vertically aligned architecture and can be integrated into operational electrochemical devices. Compared with directly deposited reference films, they exhibit lower electrode polarization and a substantially reduced apparent activation energy, demonstrating that growth-optimized nanostructures can be transferred to otherwise incompatible functional supports without compromising their electrochemical functionality. Substrate removal also enables advanced microscopy and nanoscale spectroscopy of interfaces that are difficult to access in supported films. These analyses reveal substantial cation intermixing and interfacial structural and chemical heterogeneities consistent with oxygen-vacancy accumulation. Our results establish sacrificial-layer-assisted transfer as a powerful route to connect atomic-scale investigation of complex oxide nanostructures with their large-area integration into functional electrochemical devices.