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SURF 2009: Electrochemical study of the solid-oxide fuel-cell cathode material (Ba0.5Sr0.5)(Co0.8Fe0.2)O3-d
Direct Mentor: Dr. Yong Hao <haoyong@caltech.edu>
Course Requirements:
Chemistry or Physics lab course; Introductory Materials Science course (MS 115a); Solid State Electrochemistry (MS 143)Academic Standing:
Caltech students only, sophomore or more advanced students preferred.
Background
The cathode material (Ba0.5Sr0.5)(Co0.8Fe0.2)O3-d, or BSCF for short, has the highest activity known of any material for the electrochemical reduction of oxygen gas into oxygen ions at conditions relevant to solid oxide fuel cells. As a consequence, fuel cells utilizing this material as the cathode have remarkably high power outputs. Our understanding to date is that oxygen ion flux through the bulk of BSCF is extremely high and that for typical geometries the surface reaction step is rate-limiting for the electrochemical reduction. To better quantity the reaction rate the student would study the electrochemical properties of BSCF in thin-film form.
Description
The student will fabricate thin films by pulsed laser deposition (PLD) which in turn requires preparation of a target that is used as the source material for the deposition. Powders of BSCF will be synthesized by chemical solution methods and from these the target will be prepared by standard ceramics processing methods (pressing and firing). The student will explore deposition conditions (substrate temperature, oxygen pressure, gas flow rates, etc.) to ensure that that the film composition is the same as the target and to obtain films with different crystallographic orientations. The physical characteristics of the films will be determined by x-ray diffraction (phase confirmation and evaluation of orientation) and scanning electron microscopy (film quality, thickness, and chemical composition). Electrochemical characterization will be performed by A.C. impedance spectroscopy after deposition of metallic (Au) current collectors. It is anticipated that different crystallographic orientations will have different electrochemical reaction rates.
Evaluation of the performance of solid oxide fuel cell incorporating BSCF electrodes is considered beyond the scope of this ten week SURF project.
Additional Information
Interested students should review the following references prior to contacting either Prof. Haile or the research mentor, Dr. Yong Hao. These papers will also be relevant for preparing the SURF research proposal.
H. M. Christen and G. Erez, "Recent Advances in Pulsed-Laser Deposition of Complex Oxides," J. Phys: Condens. Matter 20, 264005 (16pp) (2008).
A. Infortuna, A. S. Harvey, and L. J. Gauckler, "Microstructures of CGO and YSZ Thin Films by Pulsed Laser Deposition," Adv. Funct. Mater. 18, 127-135 (2008).
S. M. Haile, "Fuel Cell Materials and Components," Acta. Met. 51, 5981-6000 (2003).
Z. Shao and S. M. Haile, "A High Performance Cathode for the Next Generation Solid-Oxide Fuel Cells," Nature 431, 170-173 (2004).
Additional papers may be posted.
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Last modified:
February 3, 2009