MSE PhD Prospectus Defense: Emily Ghosh

MSE PhD Prospectus Defense: Emily Ghosh

TITLE: Microstructural Changes in Solid Oxide Cells After Electrolysis and Reversible Operations

ADVISOR: Soumendra Basu Mechanical Engineering, MSE

COMMITTEE: Uday Pal Mechanical Engineering, MSE; Srikanth Gopalan Mechanical Engineering, MSE; Emily Ryan Mechanical Engineering, MSE

ABSTRACT: Renewable energy resources are increasingly being introduced to meet high electrical grid energy demands and minimize global greenhouse emissions caused by widespread use of fossil fuels. However, issues of intermittency and overproduction create mismatches between energy production and grid-scale demand, necessitating long-duration energy storage. Reversible solid oxide cells (RSOCs) offer an environmentally friendly solution for energy storage as well as power redistribution. Several factors remain significant barriers to RSOC commercial viability; an important one being long-term microstructural degradation, particularly the instability of the Ni phase in the porous Ni-YSZ fuel electrodes. Ni forms a connected network across the fuel electrode, providing the electron conducting pathway between electrochemical reaction sites, making Ni connectivity, or percolation, crucial to cell performance. Prolonged high temperature operation leads to Ni coarsening and connectivity loss, resulting in reaction site deactivation and degraded cell performance. This work aims to elucidate the mechanisms of this microstructural degradation through investigation of effects of reversible operation and GDC nano-catalyst infiltration for improved performance and SOEC degradation mitigation. It was found that both chemical (i.e. temperature and humidity conditions) and electrochemical (i.e. chemical conditions plus applied electrical current) exposure during cell operation result in significant degradation via percolated Ni loss in both active layer and the support layer of the fuel electrode after SOEC operation, however RSOC operation showed to mitigate SOEC degradation in all areas of investigation. Infiltration further mitigated degradation. The combined effects of infiltration and reversible operation resulted in only a 2% loss of Ni percolation with respect to untested microstructure in the electrochemical active layer compared to the 24% loss in the same region under uninfiltrated SOEC conditions. Furthermore, greater changes were observed in the support layer as compared to the active layer, suggesting that characterizing microstructural changes in the active layer alone may not present the full picture of microstructural degradation. Low voltage SEM methods are presented to provide a holistic view of the Ni-YSZ 4-phase microstructure (percolated Ni, unpercolated Ni, YSZ, and pore) for future quantitative evaluation of microstructural evolution through various systematic studies.