Effect of H₂O and CO₂ on LSCF-GDC Composite Cathodes

Abstract

Polarization losses associated with the cathode oxygen reduction reaction (ORR) and degradation of cathode materials remain as hurdles for widespread implementation of solid oxide fuel cells (SOFC). Rates of degradation depend significantly on the operating temperature and gas conditions, such as the presence of unwanted oxygen-containing compounds, namely H2O and CO2. In this study, we explore H2O and CO2 degradation mechanisms for a common composite cathode material, La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) - Ce0.90Gd0.10O1.95 (GDC) using electrochemical impedance spectroscopy (EIS) under various temperatures, oxygen partial pressure, and contaminant conditions to determine the effect of H2O and CO2 on LSCF-GDC. Our results suggest that CO2 and H2O compete with the ORR, and a strong correlation between blocking, degradation, and sintering effects caused by CO2 and H2O is directly observed. The interactions of CO2 and H2O with the cathode surface changes as a function of operating temperature, resulting in different short-term or long-term degradation mechanisms.

Experimental Analysis of the Effect of Cathodic CO2 Supply to Industrial Solid Oxide Fuel Cells

“…As reported in Table IV, the Arrhenius plot for the LSCF-GDC cathode reveals that the activation energy is nearly unchanged when N 2 is substituted with CO 2 : this suggests a blocking of the active sites upon adsorption of CO 2 , and therefore an increase in the polarization resistance, which is not dependent on temperature. This kind of inhibiting effect of carbon dioxide agrees well with previous literature findings (2). For LSC-GDC, the ASR strongly increases, with a weak dependence on the CO 2 molar fraction.…”

“…In this application, the SOFC anode is fed with a reformate mixture, while the cathode is supplied with a mixture of O 2 and CO 2 with more than 50% CO 2 on molar basis. Hence, the SOS-CO 2 cycle encourages the investigation of the behavior of cathodic SOFC materials exposed to remarkably high concentrations of CO 2 , if compared to previous literature works (2)(3)(4)(5).…”

Overview of Approaches to Increase the Electrochemical Activity of Conventional Perovskite Air Electrodes

“…In addition, due to the presence of CO 2 in the air, the SrCO 3 carbonate phase was formed on the surfaces of the LSM- [91][92][93] and LSCF- [94][95][96] electrodes. The formation of the same insulating phases limits the oxygen exchange at the electrode-electrolyte interface and reduces the electrocatalytic activity of the LSM [97][98][99][100] and LSCF [79,[100][101][102][103][104][105] air electrodes for the ORR, followed by an increase in both the electrode ohmic and polarization resistances. Similar long-term operation tests have shown that the degradation of cells based on LSM [81] or LSCF [106,107] operating in electrolysis mode was higher than that in fuel cell mode, and when comparing two perovskite electrodes, the long-term durability of LSCF was one step ahead of that of LSM [106,108].…”

Correlating Oxygen Electrode Degradation to Cr Vaporization from Metallic Interconnects in Solid Oxide Cell Stacks

“…19,71,72 While this mechanism is a likely explanation for the poorer performance in humidified air, it does not explain the increase in degradation rate. It has been suggested that an increased degradation rate during exposure to water vapor could be related to electrode sintering (coarsening) 73 or an increased volatilization of impurities such as Si that deposit on the electrode. 70 We have recently found that purging the oxygen electrode with 40%H 2 O-O 2 during SOEC operation leads to loss of Co and Sr from the LSCF electrode due to evaporation.…”