Spatially resolved degradation behavior of a solid oxide electrolysis cell stack under CO2/H2O CO-electrolysis

High-temperature CO2/H2O co-electrolysis using solid oxide electrolysis cells (SOECs) is a promising technology for syngas production and carbon cycle closure. However, the long-term stability of multi-cell stacks remains a critical challenge due to complex internal gradients. This study investigates the degradation mechanisms of a 2-cell SOEC stack subjected to 1250 h of continuous co-electrolysis at 850 °C. The stack demonstrated relatively high stability, with a degradation rate of 4.9%/kh (125 mV/kh) during the long-term operation. A systematic spatially resolved post-mortem analysis was performed to elucidate the microstructural and compositional evolution across different regions (inlet, center, outlet; rib, channel). The results reveal distinct heterogeneous degradation behavior driven by non-uniform temperature and gas concentration distributions. In the fuel electrode, Ni particle coarsening was observed with a pronounced spatial gradient along the gas flow direction, where the maximum cross-sectional area increased from ∼20 μm2 to over ∼250 μm2 at the outlet. Furthermore, Fe-impurity-induced Ni3Fe nanoparticle growth exhibited similar spatial heterogeneity. In the air electrode, severe delamination at the LSC/CGO interface was localized in the gas inlet region. Additionally, impurity poisoning showed spatial partitioning: Mo volatilized from preheating equipment deposited primarily in the inlet and center regions, while Cr volatilized from stainless steel interconnects accumulated in the outlet region. These findings provide critical insights into the interplay between multi-physics fields and local degradation modes. This work offers valuable guidance for electrode material optimization and stack design to enhance the durability of SOEC systems for large-scale energy storage and conversion.