Surface Modification and the Long-Term Performance Stability of Ca Doped LaCoO3 SOFC Electrodes

Abstract

Development of solid oxide fuel cells highly depends on the improvement of the long-term performance stability of cathode components. In our recent study, impressive activity was detected for thin film La0.6Ca0.4CoO3 (LCC) electrodes, which were fabricated by cost-effective polymeric precursor methods (1). However, significant performance degradation, i.e., 26 times increase in area specific resistance (ASR), upon long-term exposure to 700 °C, originating from changes in surface chemistry, such as; CaO + La2O3 segregation, was observed. In the present study, to enhance the performance stability of LCC cathode, the electrode surface was modified by the oxides of its A or B-site cations, i.e., La, Ca and Co. This way, reduction of the driving force for surface segregation was aimed. Electrochemical impedance spectroscopy (EIS) measurements performed on symmetrical half-cells at 700 °C revealed that the application of the CaO overlayer did not significantly affect ASR, while CoOx or La2O3 deposition caused slight improvements. Upon prolonged exposure to 700 ° for 100 hours, the ASR increased by factors of 3.3, 2.5, and 2 in the cases of La-, Co- and Ca-oxides, respectively, corresponding to significant enhancement of the long-term stability (Figure 1). The mechanisms through which the long-term performance stability enhancements were attained was studied via X-ray photoelectron spectroscopy (XPS) measurements. Preliminary results suggest that surface modification, especially by the oxides of Ca and Co stabilizes the surface composition, which leads to a significant enhancement of long-term performance stability Figure 1. Changes in normalized area specific resistances of LCC04 and La, Ca and Co-oxide modified LCC04 electrodes upon long-term exposure to stagnant air, at 700 °C. Figure 1