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Electrical, electrochemical, and optical characterization of ceria films

Citation

Oh, Tae-Sik (2013) Electrical, electrochemical, and optical characterization of ceria films. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:05202013-113539414

Abstract

Acceptor-doped ceria has been recognized as a promising intermediate temperature solid oxide fuel cell electrode/electrolyte material. For practical implementation of ceria as a fuel cell electrolyte and for designing model experiments for electrochemical activity, it is necessary to fabricate thin films of ceria. Here, metal-organic chemical vapor deposition was carried out in a homemade reactor to grow ceria films for further electrical, electrochemical, and optical characterization. Doped/undoped ceria films are grown on single crystalline oxide wafers with/without Pt line pattern or Pt solid layer. Deposition conditions were varied to see the effect on the resultant film property. Recently, proton conduction in nanograined polycrystalline pellets of ceria drew much interest. Thickness-mode (through-plane, z-direction) electrical measurements were made to confirm the existence of proton conductivity and investigate the nature of the conduction pathway: exposed grain surfaces and parallel grain boundaries. Columnar structure presumably favors proton conduction, and we have found measurable proton conductivity enhancement. Electrochemical property of gas-columnar ceria interface on the hydrogen electrooxidation is studied by AC impedance spectroscopy. Isothermal gas composition dependence of the electrode resistance was studied to elucidate Sm doping level effect and microstructure effect. Significantly, preferred orientation is shown to affect the gas dependence and performance of the fuel cell anode. A hypothesis is proposed to explain the origin of this behavior. Lastly, an optical transmittance based methodology was developed to obtain reference refractive index and microstructural parameters (thickness, roughness, porosity) of ceria films via subsequent fitting procedure.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Conductivity; Fuel cell; Electrochemistry; thin film; refractive index
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.
Thesis Committee:
  • Haile, Sossina M. (chair)
  • Giapis, Konstantinos P.
  • Johnson, William Lewis
  • Rossman, George Robert
Defense Date:5 September 2012
Record Number:CaltechTHESIS:05202013-113539414
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:05202013-113539414
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7727
Collection:CaltechTHESIS
Deposited By: Tae-Sik Oh
Deposited On:28 May 2013 20:51
Last Modified:12 Sep 2013 16:18

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