Investigation of La_0.8Sr_0.2CoO₃/Ce _0.85Sm_0.15O_2-x cathode performance of solid oxide fuel cell by electrochemical impedance spectroscopy: Effect of firing temperature

Perovskite type complex oxide L_0.8Sr_0.2CoO _3-δ symmetrical cells were prepared on Samaria doped ceria electrolyte Ce_0.85Sm_0.15O_2-x by using the screen-printing method in a laboratory scale. The performance of the symmetrical cell was investigated by using electrochemical spectroscopy at frequency ranging from 0.1-300 kHz. Effect of firing temperature from 975-1,050°C was investigated under the controlled oxygen pressure from 0.002-0.21 atm and controlled measuring temperature from 635-782°C. The preliminary results indicated that, for all cells prepared at different firing temperatures, the SEM and XRD did not indicate any differences between them. By using EIS, however, two impedance arcs were obviously observed. This first arc was found at high frequency region (>1,000 Hz) and the second one was observed at low frequency region (<10 Hz). The high frequency arc corresponded to the impedance of electron-transfer and ion-transfer processes occurring at the current collector/electrode and electrode/electrolyte interfaces. The low frequency arc was the convoluted contribution of the diffusion processes (non-charge transfer processes). Changing firing temperature, measuring temperature and oxygen pressure leads to changing of symmetrical cell performances. The activation energy of these symmetrical cells was around 1.5-2.0 eV depending on the firing temperature and oxygen pressure.