Air electrodes and related degradation mechanisms in solid oxide electrolysis and reversible solid oxide cells

This paper reviews the existing literature on the degradation behaviour of different air electrodes used for solid oxide electrolysis cells (SOECs) and reversible solid oxide cells (RSOCs). It begins with a brief introduction to solid oxide cells (SOCs). An overview and degradation behaviour of different fuel electrodes and electrolyte materials during the SOEC operation are then provided briefly. The major focus of the current review is to understand air electrode degradation in detail. Therefore, the existing proposed mechanisms for air electrode delamination, and various studies reporting the delamination issue during SOEC operation are intensively reviewed. An introduction to RSOCs and the degradation issues for different air electrodes during RSOC tests are then discussed. Finally, mitigation strategies for delamination; recommendations for future degradation studies and some suggestions to develop more active and stable air electrodes for future SOEC and RSOC applications are presented.