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Surface Activity and Bulk Defect Chemistry of Solid Oxide Fuel Cell Cathodes

Citation

Usiskin, Robert Ezra (2015) Surface Activity and Bulk Defect Chemistry of Solid Oxide Fuel Cell Cathodes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z91N7Z3N. http://resolver.caltech.edu/CaltechTHESIS:10032014-161017442

Abstract

In the first half of this thesis, a new robotic instrument called a scanning impedance probe is presented that can acquire electrochemical impedance spectra in automated fashion from hundreds of thin film microelectrodes with systematically varied properties. Results from this instrument are presented for three catalyst compositions that are commonly considered for use in state-of-the-art solid oxide fuel cell cathodes. For (La0.8Sr0.2)0.95MnO3+δ (LSM), the impedance spectra are well fit by a through-the-film reaction pathway. Transport rates are extracted, and the surface activity towards oxygen reduction is found to be correlated with the number of exposed grain boundary sites, suggesting that grain boundaries are more surface-active than grains. For La0.5Sr0.5CoO3-δ (LSC), the surface activity degrades ~50x initially and then stabilizes at a comparable activity to that of previously measured Ba0.5Sr0.5Co0.8Fe0.2O3-δ films. For Sr0.06Nb0.06Bi1.87O3 (SNB), an example of a doped bismuth oxide, the activity of the metal-SNB boundary is measured.

In the second half of this thesis, SrCo0.9Nb0.1O3-δ is selected as a case study of perovskites containing Sr and Co, which are the most active oxygen reduction catalysts known. Several bulk properties are measured, and synchrotron data are presented that provide strong evidence of substantial cobalt-oxygen covalency at high temperatures. This covalent bonding may be the underlying source of the high surface activity.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Fuel Cells; Electrochemistry; Oxides; Catalysts; Impedance Spectroscopy; Microelectrodes
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Haile, Sossina M.
Group:Resnick Sustainability Institute
Thesis Committee:
  • Haile, Sossina M. (chair)
  • Fultz, Brent T.
  • Faber, Katherine T.
  • Rossman, George Robert
Defense Date:24 July 2014
Funders:
Funding AgencyGrant Number
Resnick Sustainability Institute fellowshipUNSPECIFIED
NSFUNSPECIFIED
SURFUNSPECIFIED
National Central University of TaiwanUNSPECIFIED
Record Number:CaltechTHESIS:10032014-161017442
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:10032014-161017442
DOI:10.7907/Z91N7Z3N
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8667
Collection:CaltechTHESIS
Deposited By: Robert Usiskin
Deposited On:17 Aug 2016 16:11
Last Modified:05 Apr 2017 20:04

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