Effect of temperature on the chromium deposition and poisoning of La0.6Sr0.4Co0.2Fe0.8O3-δ cathodes of solid oxide fuel cells

In this study, the effect of the temperature on the surface segregation and Cr deposition on La0.6Sr0.4Co0.2Fe0.8O3-a (LSCF) cathodes is investigated using confocal laser Raman spectroscopy and electrical conductivity relaxation (ECR) method. The results show that the segregation of SrO phase on the LSCF surface decreases with the decreasing of temperature. Cr deposition takes place on the LSCF surface after the heat-treatment in the presence of Cr2O3 at temperature range of 700 to 900 degrees C for 48 h, forming SrCrO4 phase. As the temperature decreases, less SrCrO4 phase is detected. The surface exchange coefficient of LSCF measured at 900, 800 and 700 degrees C after the heat-treatment in the presence of Cr2O3 for 48 h is 1.5 x 10(-4), 1 x 10(-4) and 4 x 10(-5) cm s(-1), respectively, which is much lower than that measured on the sample tested in the absence of Cr deposition. Chromium poisoning deteriorates the surface exchange and diffusion processes for the O-2 reduction reaction on LSCF electrodes. Cr deposition decreases significantly with the decrease of temperature, most likely due to the reduced Sr segregation as well as the decrease of the partial pressure of gaseous Cr species at reduced temperatures. (C) 2014 Elsevier Ltd. All rights reserved.