Semester

Summer

Date of Graduation

2023

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Xueyan Song

Committee Member

Yun Chen

Committee Member

Hailin Li

Committee Member

Jacky Prucz

Committee Member

Rakesh Gupta

Abstract

Solid Oxide Fuel cells (SOFCs) could convert the chemical energy from a variety of fuels into electricity. It has become a competitive power source due to its advantages, such as high efficiency and flexibility in fuel options. It can be operated under a wide range of operating temperatures, which makes them easy to be applied and developed into applications. To further increase the lifetime and reduce the cost of SOFC systems to make them more competitive and affordable for commercialization, the catalytic activity for oxygen reduction reaction at the cathode needs to be improved. One significant technical opportunity is to minimize the resistance to the cathode, which is the bottleneck of the performance and contributes the most to cell degradation during the operation of current SOFC systems. On the other hand, SOFC cathode materials have suffered drastically from chromium poisoning degradation. Chromium-containing species, sourcing from the stack and interconnect materials, migrate to the SOFC cathode where they can form new phases onto the cathode and even penetrate the cathode through reactions, hence, blocking oxygen pathways and slowing down the oxygen reduction reaction. Therefore, the performance of the cathode decreases, and consequently, the whole cell degrades more rapidly. Significant efforts have been made to understand the mechanism of chromium poisoning and the approach to reduce and eliminate it. In this work, baseline SOFC with cathode consisting of La1-xSrxMnO3 (LSM) is analyzed on cell degradation and change in cathode microstructure upon electrochemical operation. Cathode internal surface modification with the additive layers containing Cobalt (Co) and Manganese (Mn) has been deployed, and improvement in SOFC operation durability and power density has been achieved. A conformal layer of CoOx and dual coating of (Mn1-xCox)Oy were deposited on the porous LSM backbone, boosting the cell peak power density and specific power due to a significant reduction in polarization resistance. The coated layer enlarged the length of the triple phase boundaries (TPB) and added oxygen pathways, accelerating the oxygen reduction reaction (ORR). The electrode surface modification also significantly reduced the degradation resulting from Cr contamination in cell voltage and power density. This work provides insights into understanding the mechanisms of Cr poisoning during cell operation. It obtains critical fundamentals for designing optimal and more efficient infiltration processes and novel cathode microstructures.

Embargo Reason

Patent Pending

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