Researchers from the chemistry department at Case Western Reserve University and Toyota Central R&D Laboratories from Nagakute, Japan, have developed a theory to advance fuel cell and corrosion prevention technologies.
The researchers' work contributes to understanding what happens when platinum and platinum alloys, the most commonly used, are catalysts in fuel cells.
Ryosuke Jinnouchi from Toyota and Alfred B. Anderson, professor of chemistry from Case Western Reserve, report their findings from their two-year research collaboration in the Journal of Physical Chemistry C article, "Aqueous and Surface Redox Potentials from Self-Consistently Determined Gibbs Energies." Their article introduces a way to predict accurate descriptions of electron transfer reactions in both solution and on surfaces and how changing the applied voltage affects those reactions. A second article is being published in http://prb.aps.org/: "Electronic structure calculations of liquid-solid interfaces: a combination of density functional theory and modified Poisson-Boltzmann theory."
The Physical Review B article details the theoretical basis of the approach and introduces the mathematical formulas that were used in the computer program called Interface.
For years researchers have been mystified by the low activity of the platinum cathode. Using Interface, Jinnouchi and Anderson show preliminary evidence in the Physical Review B paper that water molecules, byproducts of the oxygen reduction reaction, bond too strongly to the cathode.
Anderson explained that to release the water, and let oxygen molecules bond to the surface of the electrode, you have to change the amount of positive or negative charge on the surface. In that process, the potential is lowered to release the water, resulting in an inefficient operation. More detailed work on this hypothesis is underway.
"This program is going to allow us to explore these reactions with different types of materials and help us find new catalyst scenarios," said Anderson.
His work is part of a broad effort including experimental works such as those by engineers Thomas Zawodzinski and Robert Savinell and other members of the Ernest B. Yeager Center for Electrochemical Science at Case Western Reserve to advance fuel cell science and technology. The work is one of the research projects of the Multi-University Research Initiative (MURI) program headed by Zawodzinski aimed at developing theoretical tools for developing fuel cells that are easily transported by backpacks for military personnel, for transportation and to power devices such as laptop computers.
Since the late 1990s, Anderson has been working on ways to take a quantum theory approach to studying electrochemistry in search of finding ways to predict the electrode potential dependencies of electrochemical reaction mechanisms and activation energies for electron and proton transfer reactions on the surfaces of electrodes.
Yu Morimoto, an alumnus of Case Western Reserve who earned his Ph.D. in 1995 and a research director at the Toyota research laboratory, sent Jinnouchi to Cleveland to pair the talents of Jinnouchi's computer programming skills with Anderson's knowledge about electrocatalysis to come up with a way to predict electrochemical reaction mechanisms and activation energies—particularly the oxygen reduction reaction on platinum cathode in fuel cells.
"During the past 10 years, my lab has provided some deep understanding of the mechanism of the oxygen reduction reaction over platinum and platinum alloy catalysts in fuel cells using theoretical models," said Anderson. "This new program allows us to rapidly try and find new catalyst scenarios, which is important because there is a desperate need to replace platinum."
Anderson explained how in hydrogen fuel cells about one-third of the voltage is lost with platinum cathodes.
"Instead of the voltage of the fuel cell being 1.2 volts (V), it is actually between 0.7 V or 0.8 V," he said, adding it is inefficient.
Better catalysts than platinum and platinum alloys are needed for the cathode and also for the anode, if fuels such as methanol are ever to replace hydrogen, according to Anderson, who will make the computer program available on request to other researchers to use in their electrochemical analyses.
The research was supported by Toyota Central R&D Laboratories, Inc. and by a Multi-University Research Initiative (MURI) grant from the Army Research Office to Case Western Reserve.
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