Date: Monday, October 26th

Time: 2 pm to 4 pm

Location: MRDC 3515, Hightower Conference Room

Committee:

Dr. Faisal Alamgir, co-advisor, MSE

Dr. Meilin Liu, co-advisor, MSE

Dr. Gleb Yushin, MSE

Dr. Preet Singh, MSE

Dr. Thomas Orlando, Chemistry

Title:
Perspectives on Degradation in Solid Oxide Fuel Cells Using X-ray Spectroscopies and Scattering

Abstract:
Solid oxide fuel cells (SOFCs) represent a major piece of a next-generation, renewable, clean energy economy and contribute to combating anthropogenic climate change by efficiently converting chemical energy into electrical energy through electrochemical reactions. However, despite adding significant chemical, mechanical, and microstructural complexity to push SOFC performance ever higher, cost and durability remain significant barriers to SOFC commercialization. Two of the issues are cathode stability in atmospheres containing carbon dioxide and water vapor and anode stability in fuel containing hydrogen sulfide.

In this work, powerful in situ and operando x-ray spectroscopy and scattering experiments provide deep insight into the physiochemical phenomena that define the behavior of SOFC electrode materials. For example, in situ x-ray absorption spectroscopy has been successfully used to tracked the charge-compensation behavior (or change in oxidation states) of both Mn and Co metal cations in a state-of-the-art LSM-infiltrated LSCF composite cathode as oxygen vacancies were introduced or removed by controlling the chemical environment and thermal annealing. To gain insight into the degradation mechanism of SOFC cathodes, operando x-ray absorption spectroscopy experiment is used to probe the evolution in surface chemistry and structure of an LSCF thin film cathode exposed to contaminants commonly encountered under practical fuel cell operating conditions. Combining in situ x-ray absorption spectroscopy and in situ pair distribution function provides evidence that sulfur exchanges with oxygen and bonds to specific metallic cations in the anode, from which the sulfur tolerance property may originate. Also, tracking transient crystalline phases with in situ x-ray diffraction indicates that water vapor may be reacting with anode byproducts to confer sulfur tolerance. Thus, the case can be made that the unique information from these experiments, partially owed to the powerful intensity and capabilities of synchrotron x-rays, can be combined for new perspectives and to better understand data where a single perspective may only lead to ambiguous conclusions. Such a multi-pronged characterization approach should ultimately lead to a better fundamental understanding of complex SOFC materials and ideally, the rational design of next-generation SOFC electrode materials.