Performance Degradation of a Double-Perovskite PrBaCo₂O_5+δ Cathode Operating under a CO₂/H₂O-Containing Atmosphere

The electrochemical activity and stability of the PBCO electrode are investigated under the annealing processes in an atmosphere containing CO₂/H₂O for solid oxide fuel cells (SOFCs). The electrochemical impedance spectrum results unequivocally confirm the significant deterioration in PBCO cathode performance upon annealing under ambient air conditions, particularly when exposed to CO₂/H₂O atmospheres. Microstructure and surface chemical state analyses reveal the segregation of BaO on the PBCO surface, and the formation of insulating BaCO₃ degraded the electrochemical performance. CO₂ and H₂O exhibit a significant induced effect on the segregation of Ba in PBCO to the surfaces, thereby causing a rapid decline in electrode performance. Additionally, the analysis of volume relaxation reveals that the presence of oxygen in the electrode environment can also influence the deposition process occurring on the surface of the electrode. However, this phenomenon is not observed in N₂. This study emphasizes the impact of various gases present in the working atmosphere on surface-separated BaO, which consequently plays a pivotal role in the activity and long-term stability of PBCO electrodes.