Nano‐Scale Characterization of Impurities Segregation in Solid Oxide Electrolysis Cells

ABSTRACT Solid oxide electrolysis cells (SOECs) offer high‐efficiency conversion of renewable electricity into chemical fuels, but their long‐term durability is limited by impurity poisoning of the Ni‐YSZ fuel electrodes. To understand the impact of polarization on impurity poisoning and microstructural degradation, we employed a novel Pt‐SiO 2 ‐Ni/YSZ/Pt model cell. For direct comparison, the Pt‐SiO 2 ‐Ni electrode was investigated under both cathodic polarization (SOEC operation) and anodic polarization for solid oxide fuel cell (SOFC) operating conditions. Post‐mortem STEM‐EDS and HRTEM analyses firstly reveal Na‐Al‐Si‐O segregation as an amorphous phase instead of crystalline along Ni grain boundaries near gas‐exposed surfaces, accompanied by Zr/Y extraction from the YSZ electrolyte and reprecipitation as fluorite phases near the Ni/YSZ interface. These phenomena are suppressed in the SOFC reference despite identical thermal exposure. The results demonstrate that ultralow oxygen partial pressures generated by cathodic polarization promote reductive dissolution of Si, Na, Al, Y, and Zr into metallic Ni, followed by rapid migration and reoxidation at sites of higher oxygen activity. The polarization‐dependent impurity transport explains accelerated degradation in high‐current SOECs. This work provides direct nanoscale evidence of the dominant degradation mechanism and offers guidance for mitigation strategies toward robust, long‐duration SOEC systems for renewable energy conversion and storage.