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Electrochemical characterization of solid acid fuel cell electrodes

Citation

Sasaki, Kenji Alexander (2010) Electrochemical characterization of solid acid fuel cell electrodes. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:05102010-184207288

Abstract

The quest for high-efficiency, high-power output fuel cells can be largely equated to the quest for high-performance components (anode, cathode, electrolyte). Solid Acid electrolytes, notably CsH2PO4, have been demonstrated to be affordable, stable, excellent ion conductors, and impermeable to parasitic fuel cross-over. Moreover, they operate at a temperature `sweet-spot' high enough to promote electrode kinetics and low enough to enable low-cost infrastructure. Fuel cell devices based on these materials are known to be limited, however, by electrode losses - even with high platinum loading. Improving the performance and lowering the cost of these components is necessary if such devices are to be considered viable alternatives. In this work, the primary focus was the development of electrochemical characterization approaches. In doing so, we investigated electrode losses through steady-state and time-dependent electrochemical characterization and identified the primary rate limiting process and mechanism as oxygen reduction at the cathode. To characterize anode kinetics, new testing approaches were implemented which employed robust, asymmetric electrode geometries to isolate electrode kinetics without the inclusion of a reference electrode. These geometries' isolation efficacy was assessed by numerical computation - the results of which were leveraged into an explicitly defined, material-agnostic tool to evaluate asymmetric electrode geometries. While for platinum, the cathode mechanism was shown to be insensitive to the microstructures tested, the mechanism of hydrogen reduction/oxidation was seen to vary between nanoscale powder and microscale defined electrodes - reconfirming the importance of rigorous testing approaches. Asymmetric electrode geometries with defined microstructures allowed direct characterization and comparative evaluation of non-platinum candidates for both the anode and the cathode. On the anode, palladium was over an order of magnitude more active than platinum and nickel, which exhibited a comparable activity. Palladium and silver were shown to be stable cathode materials, though less active than platinum. As a demonstration of the developed methodology's flexibility, a palladium-silver alloy was synthesized and tested. The tools and methodologies developed in this work enable the rapid and flexible screening of electrodes for solid acid fuel cells.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Solid Acid Fuel Cells, asymmetric electrode geometry, point electrode, microelectrode
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:
  • Giapis, Konstantinos P.
  • Ahn, Channing C.
  • Johnson, William Lewis
  • Haile, Sossina M. (chair)
Defense Date:26 August 2009
Author Email:kenji.sasaki (AT) gmail.com
Funders:
Funding AgencyGrant Number
Superprotonic, Inc.UNSPECIFIED
Record Number:CaltechTHESIS:05102010-184207288
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:05102010-184207288
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:5793
Collection:CaltechTHESIS
Deposited By: Kenji Sasaki
Deposited On:21 May 2010 16:16
Last Modified:26 Dec 2012 03:25

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