## 1 Introduction  
Solid oxide fuel cells (SOFCs) are promising energy conversion systems that directly convert chemical energy into electrical energy because of their high energy conversion efficiency, environmental friendliness and fuel flexibility. Despite these advantages, high operating temperatures (800-1000 \({}^{\circ}\)C) cause several drawbacks, such as interfacial reactions among the fuel cell components, structural deformation, chemical/thermal degradation and high material costs [1, 2]. Despite the high efficiency at high temperature, significant efforts have been made to develop intermediate temperature-SOFCs (IT-SOFCs) that can be operated at 500-800 \({}^{\circ}\)C [3, 4, 5]. To decrease the operating temperature will reduce the degradation of other components and extend the selection range of economical material, and also enhance SOFC durability. However, decreasing the operating temperature makes the electrode kinetics sluggish and increases interfacial polarization resistances. It is most prominent for the oxygen reduction reaction (ORR) that occurs in the cathode side. To satisfy the acceptable conductivities of the cathode, a sufficient electronic and oxygen ion conductivity must be maintained, as well as a high electrochemical reaction such as ORR [6, 7, 8, 9, 10]. Mixed ionic-electronic conductors (MIECs) have received considerable attention as promising cathode materials capable of achieving high performance for intermediate temperature-SOFCs (IT-SOFCs, below 800 \({}^{\circ}\)C). Among the MIECs studied so far, AA'B\({}_{2}\)O\({}_{5+\delta}\)-type layered perovskite oxides have received increasing consideration, where continuous layers of \(\mid\)BO\({}_{2}\)\(\mid\)-1 A\({}_{0}\)\({}^{-}\)\(\mid\) -1 B\({}_{0}\)\(\mid\)-1 A\({}^{\circ}\)\(\mid\) are stacked along the c-axis of the lattice. This layered structure improves the oxygen ion diffusivity by reducing the oxygen bonding strength of the [AO\({}_{\text{d}}\)] layer and generating an oxygen ion pathway [11, 12]. LnBaCo\({}_{2}\)O\({}_{5+\delta}\) (Ln = Pr, Nd, Sm, etc.) has high electrical conductivity, fast oxygen surface exchange and ion diffusion properties in the intermediate temperature range [13]. Several researchers have investigated the effect of ion substitution on the properties of the LnBaCo\({}_{2}\)O\({}_{5+\delta}\). [PERSON] et al. reported that the conductivity of YBaCo\({}_{2}\)O\({}_{5+\delta}\) increased significantly when Ba was substituted with Sr [14]. The substitution of Co with Fe enhances the structural stability due to increase in electrical conductivity and decrease in polarization resistance. [PERSON] et al. reported that PrBaCo\({}_{2}\)O\({}_{5+\delta}\) is considered one of most promising potential cathode materials for IT-SOFCs because of its low cathode polarization by rapid oxygen reduction reaction at 500-700 \({}^{\circ}\)C [15; 16]. For improving cathode performance LnBaCo\({}_{2}\)O\({}_{5+\delta}\) material, A/B-site modification is a useful method. Ba cation-deficient layered-perovskite oxide PrBa\({}_{0.92}\)Co\({}_{2}\)O\({}_{5+\delta}\) (PBO.92 CO) was evaluated as a new cathode material for IT-SOFCs. PB0.92 CO has high conductivities of 580-195 S\(\cdot\)cm\({}^{-1}\) at temperatures of 200-800 \({}^{\circ}\)C in air. ASR values of PB0.92 CO cathodes on GDC electrolytes range from 0.093 \(\Omega\cdot\)cm\({}^{2}\) at 600 \({}^{\circ}\)C to 0.0068 \(\Omega\cdot\)cm\({}^{2}\) at 800 \({}^{\circ}\)C with an activation energy of 1.05 eV [17]. For B-site modification, [PERSON] et al. [18] have reported that increased Fe doping (0 \(<\) \(x\) \(<\) 0.6) deteriorates the cathode performance of YBaCo\({}_{2}\)O\({}_{5+\delta}\). [PERSON] et al. have shown that Cu doping to PrBaCo\({}_{2}\)O\({}_{5+\delta}\) induces reduction of Co\({}^{3+}\) ion into Co\({}^{2+}\) ion and enhances electrochemical properties [19]. In our previous study, we investigated whether the polarization resistance of PrBaCo\({}_{2-x}\)Cu\({}_{x}\)O\({}_{5+\delta}\) (PBCCux, \(x\) = 0, 0.2, 0.5) decreases with Cu doping [20].