Yewon Shin

Defect study of kinetics in BCFZY0.1(Cathode) and thermodynamics in BZY20 and BCZYYb (Electrolyte)

BIO:

Yewon Shin is a second year Ph.D. student in Materials Science at Colorado School of Mines. She received the CoorsTek fellowship in 2017 and her doctoral research investigates thermodynamic and kinetic properties of protonic ceramic fuel cell (PCFC) materials. She studies the defect transport of the two popular PCFC electrolyte materials BaZr0.8Y0.2O3−δ (BZY20) and BaCe0.7Zr0.1Y0.1Yb0.1O3−δ (BCZYYb). Additionally, she is collaborating with the National Renewable Energy Laboratory (NREL) to understand the isotope exchange depth profile of PCFC cathode material, BaCo0.4Fe0.4Zr0.1Y0.1O3−δ (BCFZY0.1). She obtained a bachelor’s degree in electronic materials science engineering from Kyungpook National University in South Korea. During her undergraduate school, she did an internship at Korea Institute of Ceramic Engineering and Technology (KICET) by studying Bi2Te3. She co-authored the article “The synthesis and the pressureless sintering of Bi2Te3 for thermoelectric application” that earned a patent of processing Bi2Te3.

ABSTRACT:

Owing to the generally lower activation energy for proton conduction compared to oxygen ion conduction, protonic ceramic fuel cells (PCFCs) have demonstrated high performance at intermediate temperatures (350-600°C). Despite their promise, however, fundamental understanding of PCFC electrode and electrolyte materials remains limited. In this work, the defect transport of the new PCFC cathode material BaCo0.4Fe0.4Zr0.1Y0.1O3−δ (BCFZY0.1) developed by Duan et al. [1] and the defect thermodynamics of two of the most popular PCFC electrolyte materials, BaZr0.8Y0.2O3−δ (BZY20) and BaCe0.7Zr0.1Y0.1Yb0.1O3−δ (BCZYYb), are investigated.

18O/16O isotope exchange depth profiling (IDEP) analysis was performed by Secondary Ion Mass Spectrometry (SIMS) to determine the oxygen tracer diffusion coefficient and surface exchange behavior of BCFZY0.1. In addition to conventional diamond polished SIMS samples, we also used surface-roughened samples to simulate a porous PCFC cathode and thereby better investigate the surface reaction limited kinetics on BCFZY0.1. Improved understanding of the kinetic and transport behavior of this new cathode material will enable further optimization for PCFC application.

A comparative study of the defect thermodynamics of BZY20 vs. BCZYYb was performed using thermogravimetric analysis (TGA) by investigating the weight changes of calcined powders upon changes in pO2 between 500 – 900°C in dry and wet atmospheres. The resulting thermodynamic information is used to validate the model-based defect thermodynamic and transport properties studied by Zhu et al. [2,3]. It is our intent that a more concrete understanding of these properties for both PCFC cathode and electrolyte materials will allow the most important thermodynamic and kinetic limitations to current PCFC performance to be identified, thereby suggesting pathway to further advance PCFC development.