## 2 Materials and Methods  
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) oxides were synthesized through the Pechini method. Stoichiometric amounts of Pr(NO\({}_{3}\))\({}_{3}\cdot\)6H\({}_{2}\)O (Aldrich, St. Louis, MO, USA, 99.9%, metal basis), Ba(NO\({}_{3}\))\({}_{2}\) (Aldrich, \(\geq\)99%), Co(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O (Aldrich, \(\geq\)98%), Sc(NO\({}_{3}\))\({}_{3}\cdot\)xH\({}_{2}\)O (Alfa Aesar, Haverhill, MA, USA, 99.9%), and citric acid as chelate were dissolved in distilled water. After the proper amount of polyethylene glycol was completely dissolved, the solutions were heated to approximately 250 \({}^{\circ}\)C in air until combustion to form a fine powder of the cathode materials. The resulting powders were calcined at 600 \({}^{\circ}\)C for 4 h and ground with zirconia balls for 24 h. Samples were pressed into a pellet and sintered at 1150 \({}^{\circ}\)C for 6 h and 1200 \({}^{\circ}\)C for 4 h to prepare a dense pellet. The Ce\({}_{0.9}\)Gd\({}_{0.1}\)O\({}_{2-\delta}\) (GDC) powder for the electrolyte and the NiO-GDC powder for the anode were synthesized using the glycine-nitrate process (GNP) with stoichiometric amounts of metal nitrates and glycine. The crystalline structures of samples were determined by X-ray diffractometer (Rigaku diffractometer, Cu K\(\alpha\) radiation). The Rietveld refinement using GSAS II program was used to analyze the crystal structures and lattice parameters of the samples. The high-resolution transmittance electron microscopy (HR TEM) images were obtained with a JEOL JEM 2100F at 200 kV. The microstructures of samples were investigated using a field emission scanning electron microscope (Nova Nano SEM, FEI, Hillsboro, OR, USA). The electrical conductivities of samples were determined by a four-terminal DC arrangement with a BioLogic Potentiostat from 100 to 800 \({}^{\circ}\)C. Thermogravimetric analysis (TGA) was performed using a thermogravimetric analyzer (SDT-Q600, TA Instruments, New Castle, DE,USA) from 100 \({}^{\circ}\)C to 900 \({}^{\circ}\)C with a heating/cooling rate of 2 \({}^{\circ}\)C min\({}^{-1}\) in air. Iodometric titration was performed to measure the oxygen contents at room temperature. The samples were dissolved in HCl under inert gas atmosphere to prevent the oxidation of the I\({}^{-}\) ions. The solution was titrated with sodium thiosulfate solution. Regarding the error of this analytic method, the standard deviation values of the samples were calculated. Symmetric cells were used for the impedance spectroscopy measurement. The GDC powders were pressed into pellets and sintered at 1350 \({}^{\circ}\)C for 4 h in air to fabricate a dense electrolyte. Cathode slurries were painted onto both surfaces of the GDC electrolyte and heated at 950 \({}^{\circ}\)C for 4 h. Ni-GDC anode-supported cells (cathode/GDC/Ni-GDC) were prepared using a drop-coating method. The NiO powder, GDC powder, and starch were mixed using ball-milling in ethanol for 24 h. The mixed powders were pressed into pellets and fired at 800 \({}^{\circ}\)C for 4 h. Thin GDC electrolyte was prepared by a refined particle suspension coating technique. A GDC suspension was prepared by dispersing GDC powders (Aldrich) in a solvent with the proper amount of binder, then dispersant, and plasticizer at a ratio of 1:10. The GDC suspension was prepared by dispersing GDC powder in a solution of 2-butanone and ethanol with a small amount of polyvinyl butyral as a binder, then plasticizers such as polyalkylene glycol and butyl benzyl phthalate, and triethanolamine as a dispersant at a ratio of 1:10. The GDC suspension solution was drop-coated to the Ni-GDC anode support, followed by drying in air and co-sintering at 1400 \({}^{\circ}\)C for 5 h. For the preparation of cathode slurry, all pre-calcined electrode powders were blended with an organic binder (Heraeus V006) to form slurries.