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Position: Assistant Professor, Metallurgical and Materials Engineering, Education: B.S. Colorado School of Mines; M.S. Stanford University; Ph.D. Stanford University Research Interests: Alternative energy conversion technologies: fuel cells, solar cells, photo-electrochemistry. Micro and nano-scale electrochemical characterization, electocatalysis. Scanning probe microscopy. Impedance spectroscopy. Solid ion conductors, oxide thin-films. Research Web Page: materials.mines.edu/rc/aeml Phone: 303-273-3952 E-mail: rohayre@mines.edu |
My research focuses on using nanostructured materials to improve energy conversion technologies. In short, I hope to help solve big energy problems by thinking small. Why does thinking small provide such promise? The answer comes from a deeper understanding of the fundamental principles involved in energy conversion. Devices such as fuel cells, solar cells, and thermoelectrics produce electricity by converting a primary energy source (a fuel, light, or heat) into a flow of electrons. This conversion necessarily involves an energy transfer step, where energy from the source is passed along to the electrons constituting the electric current. This transfer has a finite rate and must occur at an interface or reaction surface. Thus, the amount of electricity produced scales with the interfacial area available for the energy transfer. Unsurprisingly, then, the desire for large surface areas has led to the use of nanomaterials.
Despite the successes brought about by the incorporation of nanostructured materials in fuel cells, solar cells, and other devices, we are still far away from possessing a solid understanding of what is really going on at the nanoscale. Many critical questions remain. For example:
What are the dimensions over which energy transfer or charge transfer reactions can effectively occur?
Is there such a thing as too small? If the periodicity of a nanostructured materials interface is smaller than the characteristic energy transfer dimension, the answer may be yes.
How do kinetic properties scale at small dimensions—is there more than simple surface area scaling at work?
As part of my Ph.D. research at Stanford University, I investigated several of these questions as they relate to fuel cells. For example, by constructing reproducible, geometrically simple, well-defined fuel cell electrocatalyst microstructures of various sizes, I explored the relationship between electrocatalyst geometry and electrochemical behavior. These experiments validated the triple phase boundary theory for polymer electrolyte membrane fuel cells. (The triple phase boundary theory recognizes that fuel cell electrochemical reactions can only occur at confined spatial regions, called “triple phase boundaries” (TPB’s) where the where the electrolyte, reactant gas, and electrically connected catalyst particles contact.)
In ongoing work, I have developed a nanoscale AFM impedance imaging technique that allows localized measurements of frequency dependent transport properties to be acquired at the sub-micron length scale. Nanometer scale visualization and measurement of impedance has proven valuable for a wide variety of fuel cell kinetic investigations— but even more intriguing potential applications exist in the study of other energy conversion systems such as solar cells, thermoelectric generators, and batteries. As an NSF International Fellow at TU Delft, I began applying these techniques to nanostructured solar cells.
This intersection between materials science and nanotechnology for energy conversion applications will likely prove to be one of the most scientifically interesting, socially valuable, and technologically fruitful areas of research over the coming decades. As identified by a U.S. Government report on basic research needs for a hydrogen economy, nanoscience introduces powerful and virtually untapped new dimensions to energy research. Current research initiatives from NSF, DOE, DOD, and DARPA reflect this belief. As a starting professor, I am targeting the following specific areas for future research:
Nanoscale characterization. I am leveraging my expertise in scanning probe microscopy to explore, characterize, and understand fundamental properties of nanoscale materials and devices. In particular, I am extending my AFM-based nanoimpedance technique into new materials domains. Also, I envision developing an AFM-based intensity modulated photocurrent spectroscopy technique for nanoscale characterization of optoelectronic devices.
Kinetic scaling effects in energy conversion. Sometimes, kinetic benefits increase non-linearly with decreasing scale. For example, recent data suggest that the performance of ultra-thin electrolyte fuel cells is often better than predicted by a simple geometric scaling relationship applied to the electrolyte thickness. Catalysis at the nanoscale also provides surprises, such as size-dependent activation/deactivation, and increasing contributions from substrate-catalyst interactions. I am studying the fundamentals of these kinetic scaling effects in geometrically well-defined thin-film systems and applying them to intermediate temperature protonic ceramic fuel cells and direct methanol catalysis.
Selected Publications (total publications ~ 20):
Book/Book Chapters:
1) Ryan O’Hayre, Suk-Won Cha, Whitney Colella, Fritz B. Prinz, (2006). Fuel Cell Fundamentals. New York, New York: John Wiley and Sons, Inc.
2) Ryan O’Hayre, Minhwan Lee, Fritz B. Prinz, Sergei Kalinin, (2007). “Frequency Dependent Transport Imaging by Scanning Probe Microscopy”. In Scanning Probe Microscopy: Electrical and Electromechanical Phenomena at the Nanoscale, Volume 1. A. Gruverman and S. V. Kalinin (Eds.), Springer Verlag, New York, New York.
Fuel Cells:
1) R. O’Hayre, T. Fabian, S. Litster, F. B. Prinz, J. G. Santiago, “Engineering Model of a Passive Planar Air Breathing Fuel Cell Cathode”, Journal of Power Sources, 167(1), 118-129, (2007)
2) T. Fabian, J. D. Posner, R. O’Hayre, S. W. Cha, J. K. Eaton, F. B. Prinz, J. G. Santiago, “The Role of Ambient Conditions on the Performance of a Planar, Air Breathing Hydrogen PEM Fuel Cell”, Journal of Power Sources, 161, 168-182, (2006)
3) R. O’Hayre, D. Braithwaite, W. Herman, S.J. Lee, T. Fabian, S.W. Cha, Y. Saito, F.B. Prinz “Development of Portable Fuel Cell Arrays with Printed-circuit Technology”, Journal of Power Sources, 124, 459, (2003)
4) R. O’Hayre, S.J. Lee, S.W. Cha, F.B. Prinz, “A Sharp Peak in the Performance of Sputtered Platinum Fuel Cells at Ultra-Low Platinum Loading”, Journal of Power Sources, 109, 483 (2002).
5) S.J. Lee, A. Chang-Chien, S.W. Cha, R. O’Hayre, Y.I. Park, Y. Saito, F.B. Prinz “Design and Fabrication of a Micro Fuel Cell Array with ‘Flip-Flop’ Interconnection”, Journal of Power Sources, 111, 410 (2002).
Solar Cells:
1) R. O’Hayre, Marian Nanu, Joop Schoonman, Albert Goosens, “Mott-Schottky and Charge Transport Analysis of Nanoporous Titanium Dioxide Films In Air”, Journal of Physical Chemistry C., 111(12), 4809-4814 (2007)
2) R. O’Hayre, Marian Nanu, Joop Schoonman, Albert Goosens, Qing Wang, Michael Grtzel, “The Influence of TiO2 Particle Size in TiO2/CuInS2 Nanocomposite Solar Cells”, Advanced Functional Materials, 16, 1566-1576, (2006)
3) R. O’Hayre, Marian Nanu, Joop Schoonman, Albert Goosens, Qing Wang, Michael Grtzel, “A Parametric Study of TiO2/CuInS2 Nanocomposite Solar Cells: How Cell Thickness, Buffer Layer Thickness, and TiO2 Particle Size Affect Performance”, Nanotechnology, 18 (5), (2007)
Microscale/Nanoscale Electrochemistry:
1) R. O’Hayre, G, Feng, W.D. Nix, F.B. Prinz, “Quantitative Impedance Measurement Using Atomic Force Microscopy”, Journal of Applied Physics, 96 (6), 3540, (2004)
2) R. O’Hayre, M. Lee, F.B. Prinz, “Ionic and Electronic Impedance Imaging Using Atomic Force Microscopy”, Journal of Applied Physics, 95 (12), 8382, (2004)
3) R. O’Hayre, F.B. Prinz, “The Air/Platinum/Nafion Triple Phase Boundary: Characteristics, Scaling, and Implications for Fuel Cells”, Journal of The Electrochemical Society, 151 (5), A756, (2004)
4) M. Lee, R. O’Hayre, T.M. Gur, F.B. Prinz, “Electrochemical Nanopatterning of Ag on Solid-State Ionic Conductor RbAg4I5 Using Atomic Force Microscopy”, Applied Physics Letters, 85 (16), 3552, (2004)
5) S.W. Cha, R. O’Hayre, S. J. Lee, Y. Saito, F. B. Prinz, “The scaling behavior of flow patterns: a model investigation”, Journal of Power Sources, 134 (1), 57, (2004)