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MSE PhD Prospectus Defense: Haoxiang Yu

TITLE: Intermediate-Temperature Solid Oxide Electrolysis Cells (IT-SOECs): A Modeling and Experimental Study of Electrochemical Performance and Degradation

ADVISOR: Srikanth Gopalan ME, MSE

COMMITTEE: Soumendra Basu ME, MSE, Uday Pal ME, MSE, Reversible solid oxide cells (RSOCs) have shown great potential for storing and releasing renewable energy by operating in solid oxide electrolysis (SOEC) and solid oxide fuel cell (SOFC) modes of operation. However, operating in SOEC mode increases the risk of material degradation, electrode delamination, cell stability, and ultimately limits system life. All the degradation modes are accelerated at higher operating temperatures and current densities. Therefore, reducing the operating temperature while maintaining acceptable cell performance is crucial for practical implementation. To understand the key constraints limiting low-temperature performance, a polarization model tailored for SOECs has been developed. This model incorporates the major polarization losses—ohmic, activation, and concentration polarization. By fitting experimental data obtained at 700 °C and 800 °C to this model, the temperature-dependent variation of each polarization contribution can be quantified and visualized. In addition to assessing temperature-related limitations, the effects of different fuel composition on cell performance have also been simulated. The potential degradation risks associated with various current densities are similarly evaluated. Besides the operating temperature, the role of materials interfaces in SOEC mode remains a major factor affecting degradation. Two types of full cells featuring oxygen electrode fabricated from Ruddlesden Popper phases Nd2NiO4+ and perovskite Lanthanum Strontium Manganite (La₀.₈Sr₀.₂MnO₃-)–were operated under harsh SOEC conditions. Post-test examination of cells was conducted using scanning electron microscopy (SEM) and Raman spectroscopy. These studies reveal that different materials exhibit distinct degradation pathways: cells featuring a barrier layer experience degradation at the electrolyte/electrode interface, while cells that directly contact the electrolyte primarily degrade within the electrode. Improving the barrier layer adherence to solid electrolyte can mitigate the interface degradation and enable operation at higher current densities.