Yewon Shin

Defect study of thermodynamics in BZY20 and BCZYYb7111 and kinetics in BCFZY4411

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:

BaC0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY4411) has been appreciated as a protonic ceramic fuel cell (PCFC) cathode material, exhibiting the triple-conduction. Also, the low activation energy for proton migration lowers the operating temperature, and heavily doped transition metal cations improve the electrical conduction.[1] For developing the application of this material, kinetic studies on surface reaction and bulk diﬀusion are essential. Thus, 18O/16O line-scnning analysis was performed by labeled time of ﬂight-secondary ion mass spectrometer (ToF-SIMS) to determine the oxygen tracer diffusion coefficient and surface exchange behavior of BCFZY4411. This will provide the knowledge of surface kinetics and bulk diﬀusion of oxygen ions in BCFZY4411, which will enable further optimization of the PCFC application.

BaZr0.8Y0.2O3-δ (BZY20) and BaCe0.7Zr0.1Y0.1Yb0.1O3-δ (BCZYYb7111) have been investigated as proton-conducting electrolyte materials due to their high performance with excellent stability and sinterability. However, the thermodynamic study of them is still rare due to the complexity of defect chemistry involving three charge carriers (proton, oxygen ion vacancy, and electron-hole). Zhu et al. ﬁtted the measured conductivity of them determined the thermodynamic properties of these two materials.[2,3] However, their studies are limited to high temperatures (600 – 900°C), and the validity of the ﬁttings is unclear yet. Thus, the defect study of BZY20 vs, BCZYYb7111 with thermogravimetric analysis (TGA) in dry atmosphere was performed to obtain defect concentrations for calculating the thermodynamic parameters. Also, a comparative study of defect modelling with the published modellings has been conducted to validate the model based defect thermodynamic and transport properties.

The intent of these studies is 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 and providing valuable fundamental data to guide the further design and modeling of these materials and resulting devices will be available.

[1] Duan, Chuancheng, et al. “Readily processed protonic ceramic fuel cells with high performance at low temperatures.” Science 349.6254 (2015): 1321-1326. [2] Zhu, Huayang, et al. “Defect Chemistry and Transport within Dense BaCe0.7Zr0.1Y0.1Yb0.1O3−δ (BCZYYb) Proton-Conducting Membranes.” Journal of The Electrochemical Society 165.10 (2018): F845-F853.
[3] Zhu, Huayang, et al. “Defect Incorporation and Transport within Dense BaZr0.8Y0.2O3−δ (BZY20) Proton-Conducting Membranes.” Journal of The Electrochemical Society 165.9 (2018): F581-F588.