Samaria-doped Ceria (SDC) was mixed with La0.8Sr0.2MnO3 (LSM) to decrease polarization resistance by enhancing oxygen reduction resistance (ORR). The increase of triple phase boundary (TPB) was observed by morphological analysis. The decrease of polarization resistance by using MIEC and improvement in durability by Fe doping to La0.8Sr0.2CoO3-δ(LSC82) were investigated in terms of structural and morphological analysis. Polyaniline nanofiber (PA) was used to improve the catalytic performance of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF6428), and the mechanism was identified in terms of morphological and chemical analysis.
In LSM-SDC composite electrode, LSM5SDC5, which is a composite electrode with same ratio of LSM and SDC, presented lowest polarization resistance value at all testing temperature. Polarization resistance of LSM5SDC5 at 700 °C was 28.08 Ωcm2, which presents the biggest difference with the value of LSM7SDC3 about 7.72%. It means that the activity of low temperature was increased by increasing triple phase boundary of LSM5SDC5.
In MIECs, Polarization resistance of LSC82 increased by about 65.7 % heat treatment as thermal stress at 900 °C for 100 hours because oxygen reduction reaction was declined by particle coarsening and aggregation of LSC82 powders. The polarization resistance of La0.8Sr0.2Co0.8Fe0.2O3-δ (LSCF8282) increased from 0.269 to 0.328 Ωcm2 after heat treatment. Increasing rate of polarization resistance of LSCF8282 was 21.9 %, which was 3 times lower than that of LSC82 due to reduced particle coarsening and aggregation by Fe doping. Particle size of LSCF8282 powders maintained about 0.5 - 3 μm, and morphologies were also similar before and after exposure to thermal stress. Chemical reaction between the LSCF8282 and Sm-doped Ceria electrolyte powders did not occur despite the thermal stress, which indicating the interface between the cathode and electrolyte is chemically stable.
In the cathode pore structure, the pore volume of the electrode layer (LSCF6428+PA) with PA pore former was increased about 3.2 times as compared with that of the existing LSCF6428 electrode layer. However, coarse pores with a diameter of 2 μm or more were observed by PA agglomeration. The specific surface area of the LSCF6428+PA electrode layer was 2.7 times higher than that of the LSCF6428 electrode layer. In PA3, it was confirmed that the contact point decreased at the interface with the electrolyte due to increased porosity. LSCF2PA1 exhibited the lowest polarization resistance at the whole measurement temperature, which is believed to be due to the fact that the LSCF6428+PA functional layer promotes the oxygen gas flow from the cell surface, thereby improving the oxygen reduction reaction. On the other hand, PA3 with electrode layer, formed only with LSCF6428+PA, exhibited the highest polarization resistance at a temperature higher than 700 °C, which was up to 47 % higher than that of LSCF2PA1. This is because the rate of oxygen ion transfer at the interface with the electrolyte is more controlled than the oxygen reduction reaction as the temperature increases.