The Solid oxide fuel cells (SOFCs) are promising alternative to combustion technology for electric energy production due to no emission and high efficiency in chemical to electric energy conversion. However, the commercialization of SOFCs is hindered by the high operating temperature, resulting in few of main problems, such as expensive system cost and short lifetime. Thus, while reduced-temperature SOFCs has been a long lasting interest in SOFC community, the sluggish oxygen reduction reaction (ORR) occurring at cathode at intermediate temperature is the most critical challenge for enhanced overall performance of SOFCs. In recent years, the surface modification of cathode materials by infiltration process shows outstanding performance. In this process, it is important to select the proper infiltrate materials since which play important role in enlarging active sites for ORR. However, the existing infiltration processes have limiting effect on performance of SOFC due to coarsening of particles at high temperature. Therefore, the selection of appropriate infiltrate materials along with the suppression of particle growth is the key requirement for enhanced ORR, dominating overall SOFC performance.

In this paper, we attempt to systemically investigate the various metal oxide as infiltrate material and extend active site for ORR by controlling the size of infiltrated oxide. The nitrate precursor of corresponding oxide was infiltrated into the cathode, La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF), in symmetric cell to test the effect of each infiltrated oxide on ORR. Among the tested samples, Pr infiltrated LSCF show lower polarization resistance (Rp) at 500 °C; 40 % lower Rp for Pr infiltrated LSCF than that of bare LSCF. Furthermore, mixed precursor of two different oxides, chemically inactive each other, were infiltrated. This process can effectively suppress particle growth at high temperature, resulting in more active site for ORR due to increased surface area. To confirm the morphology of infiltrated oxides anchored on the cathode surface, scanning electron microscope (SEM) and transmission electron microscopy (TEM) are performed.Also, electrochemical impedance spectroscopy (EIS), thermogravimetric analysis (TGA) and iodometric titration are conducted to understand correlation between produced oxygen vacancy by infiltrated oxide and ORR. In conclusion, this study shows that mixed precursor-infiltrated cathode has significant influence on ORR in SOFCs.