## 3 Results and Discussion  
The crystal structures of PrBaCo\({}_{2}\)O\({}_{5+\delta}\) (PBCO), PrBaCo\({}_{1.9}\)Sc\({}_{0.1}\)O\({}_{5+\delta}\) (PBCSc), and Pr\({}_{0.5}\)Ba\({}_{0.5}\)Co\({}_{0.9}\)Sc\({}_{0.1}\)O\({}_{3-\delta}\) (SP-PBCSc) were confirmed by X-ray diffraction (XRD) analysis (Figure 1a). The XRD patterns show a single-phase layered perovskite structure without any detectable impurities for PBCO and PBCSc. The chemical compatibility between the cathodes and the GDC electrolyte was investigated with the mixture sintered at 950 \({}^{\circ}\)C for 4 h (Figure 1b). It revealed that there were no secondary reactions between the cathodes and GDC electrolyte. Figure 1c-e exhibits the Rietveld refinement profiles with the difference between the observed and calculate XRD. (Rp = 0.19, 0.16 and 0.17 for PBCO, PBCSc and SP-PBCSc, respectively.) Crystal structures and the calculated lattice parameters are summarized in Table 1. PrBaCo\({}_{1.8}\)Sc\({}_{0.2}\)O\({}_{5+\delta}\) is labeled with SP-PBCSc because of its different crystal structure with PrBaCo\({}_{1.8}\)Sc\({}_{0.2}\)O\({}_{5+\delta}\). The samples for Sc\({}^{3+}\leq\)0.1 represent the layered perovskite phase. As shown in Table 1, PBCO shows an orthorhombic crystal structure with the Pmmm space group, while PBCSc shows a tetragonal crystal structure with P4/mmm space group. PBCO and PBCSc show a layered perovskite phase, however, SP-PBCSc with higher Sc\({}^{3+}\) substitution (Sc\({}^{3+}\) = 0.2) shows a simple perovskite cubic crystal structure with Pm\({}^{3}\)m space group. From the high-resolution transmission electron microscopy (HRTEM) images of PBCO and PBCSc, A-site ordering layered structures were observed showing a weak additional spot in the fast-Fourier transformed pattern, which are indexed with (001) of layered double perovskite. (Figure S1a,b) Meanwhile, HR TEM image of SP-PBCSc (Figure S1c) shows the fast-Fourier transformed pattern indexed with (001) of cubic perovskite. The microstructures of the PBCO and PBCSc were investigated using scanning electron microscopy (SEM) as presented in Figure 2. The similar microstructures of PBCO and PBCSc indicate that Sc\({}^{3+}\) substitution does not affect the morphological property of the cathode materials. As shown in Figure 2c, a dense GDC electrolyte (\(\sim\)10 \(\upmu\)m thick) and a porous PBCSc cathode (\(\sim\)25 \(\upmu\)m thick) are successfully fabricated without delamination between them. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Sc** & **Cathode** & \begin{tabular}{c} **Space** \\ **Group** \\ \end{tabular} & **a (Å)** & **b (Å)** & **c (Å)** & \
\begin{tabular}{c} **Unit Cell** \\ **Volume (Å\({}^{3}\))** \\ \end{tabular} &
\begin{tabular}{c} **Oxygen** \\ **Content** \\ \end{tabular} \\ \hline
0 & PrBaCo\({}_{2}\)O\({}_{5+\delta}\) & _Pmmm_ & 3.91914 & 3.84016 & 7.85418 & 118.206 & 5.68 \\
0.1 & PrBaCo\({}_{1.9}\)Sc\({}_{0.1}\)O\({}_{5+\delta}\) & _P4/mmm_ & 3.92141 & 3.92141 & 7.72105 & 118.730 & 5.64 \\
0.2 & Pr\({}_{0.5}\)Ba\({}_{0.5}\)Co\({}_{0.9}\)Sc\({}_{0.1}\)O\({}_{3-\delta}\) & _Pm3m_ & 3.90801 & 3.90801 & 3.90801 & 59.685 & 2.80 \\ \hline \end{tabular}
\end{table} 
Table 1: Space group and lattice parameters of PBCO, PBCSc and SP-PBCSc. Figure 1: **(a)** X-ray diffraction (XRD) patterns of PrBaCo\({}_{2}\)O\({}_{5+\delta}\) (PBCO), PrBaCo\({}_{1.9}\)Sc\({}_{0.1}\)O\({}_{5+\delta}\) (PBCSc), and Pr\({}_{0.5}\)Ba\({}_{0.5}\)Co\({}_{0.9}\)Sc\({}_{0.1}\)O\({}_{3-\delta}\) (SP-PBCSc). **(b)** The chemical compatibility between the cathode materials and Ce\({}_{0.9}\)Gd\({}_{0.1}\)O\({}_{2-\delta}\) (GDC). Difference between the observed and calculated XRD profile of **(c)** PBCO, **(d)** PBCSc and **(e)** that of SP-PBCSc. Figure 2: Scanning electron microscope image of **(a)** PBCO, **(b)** PBCSc and **(c)** a cross-section consisting of the GDC electrolyte with porous cathode and Ni–GDC anode. Figure 3a shows the temperature dependence of the oxygen non-stoichiometry for PBCO and PBCSc by thermogravimetric analysis (TGA) in air.