Long-term electrochemical performance of polymeric precursor-derived films of LaCoO 3 doped with Ca 2+ (LCC), instead of the larger Sr 2+ which segregates at the electrode surface forming oxides/hydroxides, was investigated in the present study. It was determined that pre-calcination at 800 °C (LCC02-800) resulted in a higher electrochemical performance but a poorer long-term stability than those pre-calcined at 700 °C (LCC02-700) or 900 °C (LCC02-900). Increasing Ca 2+ content (LCC04-800) enhanced the initial electrochemical performance slightly, while causing a much poorer long-term stability. Microstructural evolution analyses revealed that, although it had some impact on the initial and long-term performance of LCC electrodes, it was not the strongest influence. It was determined via XPS analyses that formation of CaO and CaO + La 2 O 3 layers at the LCC02-800 and LCC04-800 surfaces, respectively, accompanied by a decrease in the relative amounts of adsorbed oxygen species (corresponding to surface oxygen vacancies) caused a faster performance degradation in these samples than those pre-calcined at 700 or 900 °C. Eventually, only the surface cation ratio of LCC02-700 became close to the theoretical one after long-term operation.

Development of solid oxide fuel cells strongly 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, fabricated by cost-effective polymeric precursor methods. 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 and 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.

It is now established in porous (La,Sr)­CoO3 (LSC) solid oxide cell electrodes that Sr2+ dopant, employed mainly to generate oxygen vacancies, tends to form an insulating SrO/SrCO3/Sr­(OH)2 phase at the electrode surface, diminishing its oxygen exchange ability. Replacing Sr2+ with Ca2+ (switching from LSC to LCC) is likely a viable approach to the mitigation of surface segregation due to the closer match of cation radius of the latter to that of La3+. In order to determine the effect of dopant replacement on the phase and surface chemistry evolution alone, the influence of microstructure evolution on the performance degradation rate must be eliminated. Therefore, here, we compared the surface chemistry and phase evolutions of LSC and LCC on bulk, dense ceramics, which did not undergo notable changes in active surface area. To track electrochemical performance evolution, we determined the changes in the oxygen surface exchange (k chem) and oxygen diffusion coefficients (D chem) via electrical conductivity relaxation (ECR) measurements performed prior to and after 100 h exposure to 700 °C. LCC had higher k chem than did LSC, but D chem values were similar. Similar performance degradation behaviors, but via different mechanisms, were observed. Obtained information is useful for both solid oxide cell and separation membrane applications.