High performance Bi-layered electrolytes via atomic layer deposition for solid oxide fuel cells

• Feasibility of ultra-thin protective layer for a stable and high-performing SOFC.
• Validates a theoretical guideline for bi-layered electrolytes prepared by ALD.
• Chemical and structural stability of bi-layered electrolytes in various environments.
• Useful design/operational guidelines for IT-SOFCs using bi-layered electrolyte scheme.

This study investigates the functionality of bi-layered electrolytes in intermediate temperature solid oxide fuel cells. A thin yttria-stabilized zirconia (YSZ) layer is expected to protect the underlying gadolinia doped ceria (GDC) electrolyte from being chemically reduced and significantly improve cell stability and durability. Although a thinner YSZ layer is preferable to minimize ohmic loss, there are limitations as to how thin the YSZ film can be and still serves as a valid protection layer. The limitation is partially attributed to the inter-diffusion and significant morphological changes during the high temperature sintering processes. In this study, a stable operation was demonstrated for extended duration (>80 h) with only a 28 nm YSZ layer (corresponding to a YSZ/GDC thickness ratio of 6.5 × 10−5) when limitations in both fabrication (<∼800 °C) and operating conditions (<∼600 °C, dry H2) were imposed. Furthermore, the functionality of a protection layer with a given thickness was found to strongly depend on the method of depositing the protective layer. Protective layers deposited by atomic layer deposition (ALD) can be much thinner than those prepared by physical vapor deposition; the YSZ/GDC thickness ratio for a stable operation approached close to a theoretical value when the ALD was used.

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