A fundamental study of chromium deposition and poisoning at (La 0.8Sr 0.2) 0.95(Mn 1− xCo x)O 3 ± δ (0.0≤ x ≤1.0) cathodes of solid oxide fuel cells

Abstract

Fundamental understanding of the chromium deposition and poisoning is very important in the development of intermediate temperature solid oxide fuel cells (IT-SOFCs) based on metallic interconnect. In this paper, chromium deposition and poisoning at the (La 0.8Sr 0.2) 0.95(Mn 1− x Co x )O 3 ± δ (LSMC, 0.0 ≤ x ≤ 1.0) cathodes are systematically studied in the presence of a chromia-forming metallic interconnect under SOFC operation conditions. The results show that as the B-site Mn is substituted by Co, electrochemical activity of the cathodes for the O 2 reduction reaction increases due to the increased oxygen exchange coefficient and oxygen diffusion coefficient as a result of the increased oxygen vacancies of the LSMC perovskite. However, in the presence of a chromia-forming metallic interconnect, chromium deposition on the electrolyte surface in contact with the LSMC electrode decreases while on the electrode surface it increases as Co content in LSMC increases from 0.0 to 1.0. On the other hand, the chromium poisoning effects as measured by the increase in the overpotential and electrode polarization resistance are most pronounced for the LSMC cathode with x = 0.4. The occurrence of the maximum chromium poisoning is most likely due to combined poisoning effect of the Cr deposits at the electrode surface and electrolyte surface on the kinetics of the O 2 reduction reactions. The results clearly indicate that the increase in the electrochemical activity of the cathode does not necessarily lead to the reduction in the chromium deposition. Rather, the changes in the electrochemical activity of the LSMC cathodes simply change the distribution pattern of chromium deposition on the electrode and electrolyte surface. Chromium deposition at LSMC cathode is closely related to the chemical affinity and stability of the manganese and strontium species, which depends significantly on the Co/Mn ratio at the B-site of the LSMC perovskite.