THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

GEORGIA INSTITUTE OF TECHNOLOGY

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Thursday, March 8, 2018

1:00 PM
in MoSE 3201A

will be held the

DISSERTATION PROPOSAL DEFENSE

for

Ryan Murphy

"Improving the Stability and Performance of Barium Perovskites for Solid Oxide Fuel Cells"

Committee Members:

Prof. Meilin Liu, Advisor, MSE

Prof. Hamid Garmestani, MSE

Prof. Preet Singh, MSE

Prof. Mark Losego, MSE

Prof. Angus Wilkinson, CHEM

Abstract:

Barium based perovskites have been studied as proton conductors for several decades.  In recent years, their success as proton conductors has allowed them to become the state of the art electrolyte materials for solid oxide fuel cells (SOFCs) and solid oxide electrolyte cells (SOECs).  However, their instability against carbon dioxide and water has limited their ability to be widely adopted.  Often barium is blamed for their instability because the degradation products are typically barium carbonate or barium hydroxide.  However, attempts to replace or reduce barium have resulted in conductivities too low to be viable.

This study will focus on the fabrication and study of novel BaMO3 systems in an effort to reduce degradation and/or increase conductivity.  Several potential systems will be outlined but are subject to changes through the efforts of DFT work currently in progress in the research group.  The current state of the art system for SOFC electrolytes is BaZr0.1Ce0.7Y0.1Yb0.1O3.  The first effort to improve stability is the replacement of zirconium with hafnium.  BaHfO3 is more thermodynamically stable than BaZrO3 indicating less hafnium will be needed to achieve the same  stability as zirconium.  The second system is BaCeO3 with alkali metals doped into the barium site.  This would have the dual effect of improving conductivity and increasing stability by reducing the barium content of the system.  The final system will combine the best performers from both earlier systems with novel trivalent dopants into the cerium site in order to further improve the conductivity by increasing charge carriers either through increased oxygen vacancies or increased water absorption.  Finally, the best overall chemical systems will be used to create full fuel cells and electrolysis cells in order to test their performance and stability in real operation conditions.