To minimize alteration of the La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)/Gd0.2Ce0.8O2-δ(CGO20)/Y0.06Zr0.94O2-δ(3YSZ) interface via strontium zirconate formation in solid oxide cells, electron beam physical vapor deposition was employed to manufacture dense, thin gadolinium-doped ceria (CGO) interlayers. CGO layers with thicknesses of 0.15, 0.3, and 0.5 μm were integrated in state-of-the-art 5 × 5 cm2-large electrolyte-supported cells, and their performance characteristics and degradation behavior were investigated. Electrochemical impedance spectroscopy measurements are correlated with a postmortem scanning electron microscopy/energy-dispersive X-ray spectroscopy analysis to show that 0.15 μm-thick layers lead to the formation of a continuous Sr-containing secondary phase at the CGO/YSZ interface, likely related to the formation of a SrO-ZrO2 phase. Major performance losses were confirmed by an increase in both Ohmic and polarization resistance with an increase in the frequency region ∼103 Hz. Cells with 0.3 μm- and 0.5 μm-thick CGO layers showed similar high performance and low degradation rates over a testing period of ∼800 h. The YSZ/CGO interface of the cells with a 0.3 μm-thick CGO layer showed the formation of a discontinuous Sr-containing secondary phase; however, performance losses were still successfully prevented. Furthermore, it is observed that 0.5 μm-thick CGO layers were sufficient to suppress the formation of the Sr-containing secondary phase.
Keywords: ESC; Gd-doped ceria (CGO); physical vapor deposition (PVD); residual stress; solid oxide fuel cell (SOFC); zirconate.