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Sustainable energy has emerged as the most pressing challenge facing humanity in the 21st century. Fuel cells, because of their high efficiencies and benign emissions, will likely play an important role in a sustainable energy future. In this work we hope to leverage new materials discovery against tailored architectures in order to obtain unprecented fuel cell power outputs.
Solid acids are a fascinating class of materials built upon hydrogen bonded oxyanion groups. In contrast to polymeric proton conductors, these compounds conduct protons without the assistance of mobile water molecules, opening new technological possibilities and scientific avenues. Our success in fabricating and demonstrating fuel cells based on these electrolytes has lead to the spin-off company, Superprotonic Inc.
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Here's a "popular press" article on our solid acid fuel cells which appeared in the Caltech publication ENGenious.
- And here's a video put together by Science and Technology News Network.
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Several oxides of the perovskite structure, notably BaCeO3, BaZrO3, SrCeO3 etc., can, after appropriate doping so as to contain oxygen vacancies, adsorb significant quantities of water into their bulk structures. The protons associated with the incorporated water are present in the form of hydroxyl groups and can easily migrate from one oxygen ion to the next. This easy migration results in a high conductivity and materials that are useful for a range of devices, from fuel cells to hydrolysis cells to hydrogen separation membranes.
- Solid
Oxide Fuel Cells
Solid oxide fuel cells (SOFCs) operate at high temperatures, and, as a consequence, they can utilize hydrocarbon fuels, they provide for efficient catalysis, and they exhaust 'high quality' waste heat that can be used for additional power generation. High temperature operation, however, has generally been responsible for the high cost of SOFCs and for their undesirability for portable applications. Our efforts in solid oxide fuel cells span a number of activities. These include the use of ceria as an electrolyte for reduced temperature operation, the incorporation of ceria in fuel cell anodes for enhanced electrooxidation activity for complex hydrocarbon fuels, the development of alternative perovskite cathodes for high activity oxygen electroreduction, and the operation of fuel cells in so-called single chamber mode for portable power.
- Thermoelectric
Materials and Devices
Thermoelectric materials are useful for converting heat into electricity (power generation), or, conversely, for extracting heat using electricity (cooling). Such materials must combine low thermal conductivity, high electronic conductivity and high Seebeck coefficient, where Seebeck coefficient is the ratio of the voltage generated across a material in response to an applied temperature gradient. The strategy we employ to achieve this somewhat contradictory set of properties incorporates both semiconductor materials with complex crystal structures and microstructural manipulation by rapid quenching. For a general overview of thermoelectrics and some fun demos, visit the JPL TE page.
- Ferroelectric Materials and Actuators (leaving this site)
Over the past several years, ceramic actuators have been developed based on Pb(Ti,Zr)O3, or PZT, because of its high piezoelectric coefficients. In this work we use structural much simpler compounds, BaTiO3 and PbTiO3 and intermediates, to develop microactuators. The strategy is to take advantage of the domain reorientation that occurs in these tetragonal, ferroelectric materials upon application of an electric or mechanical field. Strains of 1 to 6 % can, in principle, be obtained. The success of this approach relies on the preparation of highly oriented thin films. Our synthetic strategy is based on the sol-gel technique of oxide synthesis.
People and AgenciesMany silicates are relatively good conductors of alkali ions. Such materials serve as excellent model systems for study because a wide variety of crystal structures can be obtained. Moreover, the structures are typically anisotropic, and thus the impact of subtle differences in structural features can be probed via measurements along different directions.
- Research Group Members - the people who make it work!
No post-doctoral positions are currently open.
SURF projects for 2009 - All positions are now filled.
- Synthesis and Characterization of Proton Conducting Solid Electrolytes:
Cs5H3(SO4)4 and (Cs1-xRbx)5H3(SO4)4Junior or sophomore Caltech students with prior research experience preferred, and in some cases only Caltech students will be considered. See individual project descriptions for course requirements and recommended prior experience.
In addition to applying through the SURF program, Interested candidates should send a CV, transcript and at least one letter of recommedation to Prof. Sossina Haile and the direct laboratory mentor specified in the project description, before requesting further information. Please do not rely on the SURF office to forward this information.
You may also be able to pursue research in the Haile laboratory via the National Science Foundation summer research program in solid state and materials chemisitry, run by the University of Oregon. This program is primarily for non-Caltech students with US citizenship or permanent residency. Please visit
to apply. While the Haile group laboratory may not be specifically listed as one of the host laboratories, if you are interested in that program and in one of the projects listed here, it is possible that arrangements can be made.
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Last modified:
February 10, 2009