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Sossina M. Haile, California Institute of Technology, DMR 0604004

A careful study of hydrogen electrocatalysis on doped ceria anodes shows that the oxide surface is exceptionally active for the fuel electro-oxidation. In fact, platinum current collectors introduce no additional activity, despite the widely held expectation that catalysis in such a structure should be localized to the triple-phase boundaries at which the oxide, the metal, and the gas phase are in simultaneous contact. With this insight, then graduate student William Chueh created ceria electrodes of high specific surface area by pulsed laser deposition. Characterization of these structures by post-doctoral scholar WooChul Jung reveals the structures to have extremely low polarization resistance, below that of most metal-ceramic composite electrodes. Introduction of a small amount of dispersed Pt catalyst particles achieves another factor of three increase in activity.

Electrochemical reaction impedance of ceria structures (T = 650 oC, pH2 = 0.4 atm, pH2O = 0.005 atm, balance Ar). Smaller arcs correspond to higher activity.

0 2 4 6 80

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Dense and flat Porous and columnar Columnar with Pt catalyst

0.3 cm2

2.4 cm2

7.2 cm2

1 mm

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Sossina M. Haile, California Institute of Technology, DMR 0604004“Solid State Electrochemistry for Energy Storage and Conversion” is a new course developed by Sossina Haile co-listed in Materials Science and in the new Caltech subject area, Energy Science and Technology. Each lecture is video recorded and notes captured electronically. The entire course content is available on-line for unrestricted worldwide access. Catalog description: Thermodynamics and kinetics of ion and electron transport in solids, with emphasis on processes in electrolyte and electrode materials used in energy storage and conversion. Treatment of electroanalytical characterization techniques including a.c. impedance spectroscopy, voltametry, and d.c. polarization methods. Application areas include fuel cells, electrochemical gas separation membranes, batteries, supercapacitors, and hydrogen storage materials.

http://win-dms-ms1.caltech.edu/five/Catalog/pages/catalog.aspx?catalogId=62a106e4-616b-48c0-834a-c640e502ae83

MS/EST 143 Lecture 4/22/2011