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Q & AJune 30, 2008Penn State's Craig Grimes Energy
Research News Editor Eric Smalley carried out an email conversation
with Craig
Grimes, a Professor of electrical engineering at Pennsylvania
State University.Grime's research is in hydrogen generation, solar cells, materials for controlling electromagnetic energy, and environmental sensors. His lab has developed a method of producing dense arrays of titanium dioxide nanotubes of the optimal sizes and shapes for turning light into electricity. His team has used the nanotubes to extract hydrogen from water, generate useful amounts of electricity, and study fundamental aspects of light harvesting, charge separation and charge transport. Grimes has written more than 250 journal articles, a dozen book chapters, and twenty patents. He is founder or co-founder of four companies. He is co-author of The Electromagnetic Origin of Quantum Theory and Light, editor of The Encyclopedia of Sensors, and co-author of Light, Water, Hydrogen: The Solar Generation of Hydrogen by Water Photoelectrolysis. Grimes was born and raised in Ann Arbor Michigan. He received B.S. degrees in electrical engineering and physics from Pennsylvania State University in 1984, and a Ph.D. degree in electrical and computer engineering from the University of Texas at Austin in 1990. In 1990 he joined the Lockheed Palo Alto Research Laboratories where he worked on artificial dielectric structures. From 1994 to 2001 Grimes was a faculty member of the Electrical and Computer Engineering Department at the University of Kentucky. ERN: What are the important or significant trends you see in energy research? CG: The trends I see are: (1) People are becoming aware that we have a problem. (2) Much effort and resources expended in the wrong direction, i.e. food into SUV fuel. (3) The beginnings of significant (larger scale) solar energy conversion research, but unfortunately not in the United States. ERN: What would you like to see happen? Is this different from today's national and global energy research priorities? CG: A clear look at the numbers indicates that beyond a miracle, e.g. nuclear fusion somehow made to work, the only way out of the energy/global warming end game are means of economically (i.e. using earth-plentiful resources) converting sunlight into electricity and/or chemical fuel. ERN: What is the general focus of your research, and how does it relate to energy? CG: My research group is working towards material architectures for efficiently converting sunlight into electricity or chemical energy -- notably hydrogen by water splitting, using materials that are still relatively plentiful in the earth's crust. The 'plentiful in the earth's crust' is a key point. The world population is so huge that we are rapidly burning through many of the known reserves of certain elements. So if you come up with a great solar cell but it requires indium or platinum, you have a problem. ERN: Your work with titanium dioxide nanotubes has applications in both hydrogen generation and photovoltaics. How is nanotechnology significant for energy research? CG: Conversion of sunlight into photogenerated charge, and then useful collection of that charge, is an interface problem. That is to say, we need to understand and be able to control material properties at their interface, i.e. boundaries with other materials. Our work on the nanotube arrays is one approach to that. It's a controlled interface of specific, large surface area geometry. The ordered array gives rise to facile charge transport. The nanoscale features of the geometry facilitates charge separation. ERN: Solar water splitting -- using the sun's energy and a catalyst to break the bonds in water molecules -- promises to be a very clean method of generating hydrogen for fuel. What's the state of solar water splitting research, and what are the hurdles and milestones ahead? CG: It's a tough problem. One needs materials of the correct bandgap (like iron oxide) so they capture a large fraction of the incident solar spectrum energy. The materials need to have excellent charge transport properties, like TiO2 [titanium dioxide], so the photogenerated charge can be collected to do useful work (as opposed to having the photogenerated charge not separate and hence simply recombine). Then you need material to be resistant to photocorrosion, like SrTiO3 [strontium titanate]. The desired properties can work against each other in a circular manner. For example photogenerated holes, rather than oxidize water, which is what we would like them to do, tend to attack materials having 'low' bandgaps (i.e. the very same materials that are suitable for capturing a significant fraction of the solar spectrum energy). Materials having 'large' band gaps, e.g. TiO2, are almost impervious to photocorrosion but capture only a small fraction of the incident solar spectrum light (about 4%). ERN: What are some of the strategies you and other researchers are investigating? CG: Well, basically tricking materials with suitable band gaps into behaving, with respect to photocorrosion, like they have a large bandgap. Different geometries to minimize unwanted recombination, e.g. the nanotube arrays with wall thickness less than the minority carrier diffusion length. And, like mother nature's photosynthesis, coming up with device architectures where two low energy photons are coupled together to split water. single page | 1 2 3 next > Back to ERN June 30, 2008 |
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