Ultra-thin film solid oxide fuel cells utilizing un-doped nanostructured zirconia electrolytes

► Thin film SOFCs fabricated based on un-doped nanostructured ZrO2 electrolytes. ► ZrO2-based membranes are thermo-mechanically robust during fuel cell operation. ► Power density of ∼33 mW cm−2 was achieved with OCV of ∼0.91 V at 450 °C. ► SOFC functional properties are sensitive to electrolyte thickness. ► Post-deposition annealing enables tuning SOFC characteristics.