8YSZ/(La0.8Sr0.2)0.95MnO3–δ cathode performance at 1–3 bar oxygen pressures

Pressurised operation of solid oxide fuel cells (SOFC) has been shown to significantly improve their performance (Singhal, 2000) [1], however little work has been done on the effects of pressure on SOFC cathodes. The effect of pressurised oxygen on the area specific polarisation resistance (ASRp) of (La0.8Sr0.2)0.95MnO3–δ/8YSZ SOFC cathodes was determined by electrochemical impedance spectroscopy (EIS). Pellets of 8YSZ were pressed and sintered at 1350 °C, and screen printed layers of LSM/8YSZ cathode and LSM current collector were applied and sintered at 1300 °C and 1200 °C respectively. EIS was carried out between 1 and 3 bar oxygen at 800–1000 °C. One process dominated the spectra, and was identified as process C, (Jorgensen and Morgensen, 2001) [2] by comparison of measured and reference frequency maxima, the dependence of polarisation resistance on PO2, the capacitance, and the activation energy. It is suggested that this represents the physical process of dissociative adsorption of oxygen at the triple phase boundaries of the electrode. A second process, with a magnitude almost independent of PO2, is observed, which may be process B [2], related to transport of oxygen ions in the YSZ.

Research Highlights
► We test LSM-YSZ SOFC cathode symmetrical half cells by EIS in pressurised oxygen.
► EIS spectra are modeled with an electrical equivalent circuit, showing two arcs.
► EIS arcs are compared to literature, large arc is dissociative adsorption of oxygen.
► The small arc is transport of oxide ions through YSZ.
► Polarisation resistance decreases with increasing oxygen pressure from 1 to 3 bar.