Role of phosphorus impurities in decomposition of La2NiO4-La0.5Ce0.5O2-δ oxygen electrode in a solid oxide electrolysis cell

This study explored the decomposition mechanism of a La2NiO4 (LNO) phase in the La2NiO4-La0.5Ce0.5O2-delta (LNO-LDC) oxygen electrode in a solid oxide electrolysis cell (SOEC) after testing at 800 degrees C. Scanning electron microscopy and scanning transmission electron microscopy examinations of the LNO-LDC oxygen electrode before and after testing were undertaken. Other than phosphorus contamination in the form of P-rich grains and P-rich deposits along all grain boundaries (GBs), LNO and LDC phases were intact without degradation in the as-fabricated electrode. However, mild to aggressive LNO phase decomposition triggered by the phosphorus poisoned GBs was observed after testing at 800 degrees C for 900 h. The evolution of the LNO phase decomposition was noted beginning with the exsolution of Ni into the surrounding LNO matrix and GBs, forming La-rich and Ni-rich phases correspondingly, in the LNO. This study illustrates a detailed decomposition progress of the LNO phase at the atomic level under an SOEC operation condition, and sheds light on how to ameliorate the fabrication process of SOECs to enhance their performance and durability.