In this research supported by the Analytical and Surface Science Chemistry Program, magnetic effects on electron transfer processes are investigated and modeled. Electron transfer processes and magnetic fields are ubiquitous and coupled through the electron spin, but the role of magnetic fields in electron transfer is poorly understood. From our prior work, magnetic modification of electrodes substantially enhances currents for academically interesting redox probes and for technologically important power sources including fuel cells and batteries. In this project, models for magnetically enhanced reaction kinetics will be developed by imposing magnetic field and spin terms on extant models of electron transfer. The models will be tested against existing data and data newly collected in light of the modeling results. The models will advance theoretical and experimental science.

Some broader impacts of facilitating electron transfer rates by magnetic modification are apparent from our prior work: fuel cells with higher power density and carbon monoxide tolerance, platinum catalysts tolerant to carbon monoxide, and alkaline batteries with higher accessible energy density that are also made rechargeable. All are potentially transformative technologies. Appreciation of why magnetic fields facilitate these processes will advance the understanding of electron transfer reactions as well as lead to markedly more efficient development of other technologies. The project is highly multidisciplinary and integrates distinct fields of chemistry, a research matrix that leads to better trained students.

Project Report

Electrochemical reactions occur in bulk phases and at electrodes. Electrochemical reactions transfer of electrons; at electrodes, electron transfer is measured as current. Higher current means higher efficiency. In electron transfer, both electron spin and charge must transfer. Understanding of electron transfer is based largely in electrostatics, where charge interacts with electric fields. Less commonly considered is the spin that characterizes magnetic properties and interacts with magnetic fields. Research at the University of Iowa shows that introduction of micromagnets to electrodes increases current. Increased current corresponds to increased efficiency in electrochemical energy storage and generation systems such as batteries, fuel cells, and solar cells. This NSF grant explored technologically important electrochemical energy systems and fundamentals of magnetic effects on electron transfer. Interplay of technology and science promotes more efficient devices and theory that better designs electrochemical technologies. The technologies advanced under this grant are: Primary (disposable) alkaline manganese dioxide batteries with 25 to 40 % higher efficiency than nonmagnetic batteries A proof of concept system for hydrogen gas generation at magnetically modified p-Si semiconductor electrodes with sunlight. In strong acid, photoconversion efficiencies approach 6 %. Improved hydride storage electrodes Prior NSF funding for magnetically modified electrodes demonstrated improved fuel cells for hydrogen, reformat, and liquid (e.g., methanol and ethanol) fuels as well as electrodes for nickel metal hydride and rechargeable manganese dioxide batteries. Increased efficiency by incorporation of micromagnets on electrodes is demonstrated across numerous electrochemical energy systems. Typically, efficiency is enhanced 25 to 40%. Fundamentally, data for academically interesting redox probes is modeled through modification of classical transition state theory to conclude: Electron transfer rate, characterized as current, increases with incorporation of micromagnets. Higher strength magnetic materials and higher magnet loadings drive larger enhancements. Current increases with magnetic field. Current increases with magnetic properties of electroactive species. Entropy is reduced on incorporation of micromagnets. Theoretical developments enable design of better electrochemical energy storage and generation technologies. This NSF grant has yielded numerous patent applications and contributed to the support of six doctoral dissertations and one master's thesis. These students developed other energy projects. Improved theory and electrochemical energy systems serve societal energy needs because electrochemical energy is renewable with less environmental tax than thermal combustion. Electrochemical reactions occur in bulk phases and at electrodes. Electrochemical reactions occur by transfer of electrons; at electrodes, electron transfer is measured as current. To transfer an electron, both the spin and charge of the electron must transfer. Understanding of electron transfer in electrochemical systems is based largely in electrostatics, where charge interactions with electric fields. Less commonly considered is the spin that characterizes the magnetic properties of the electron and how electrons interact with magnetic fields. Research at the University of Iowa has shown that introduction of micro-magnets to electrode surface increases current substantially. Increased current corresponds to increased efficiency in electrochemical energy storage and generation systems such as batteries, fuel cells, and solar cells. This NSF grant explored both technologically important electrochemical energy systems and fundamental understanding of magnetic effects on electron transfer rates. The interplay of technology and science promotes development of more efficient devices and theory that leads to better design paradigms for electrochemical technologies. The technologies advanced under this grant are: Primary (single use) alkaline manganese dioxide batteries with 25 to 40% higher efficiency than comparable non-magnetic batteries across the range of discharge rates. A proof of concept system for the generation hydrogen gas at p-Si semiconductor electrodes with sunlight. In strong acid, photo conversion efficiencies of hydrogen ion to hydrogen gas approach 6%. An improved hydride storage electrode Prior NSF funding for magnetically modified electrochemical systems has demonstrated improved fuel cells for hydrogen, reformat, and liquid (e.g., methanol and ethanol) fuels as well as electrodes for nickel metal hydride and rechargeable manganese dioxide batteries. The idea of increased efficiency by incorporation of micro-magnets of electrode surfaces is thereby demonstrated across a wide range of electrochemical energy systems. Fundamentally, data collected for academically interesting redox probes has been modeled through modification of classical transition state theory to yield conclusions that include: The rate of electron transfer is characterized as the current. Current increases with incorporation of micro-magnets. Larger current enhancements are observed with higher strength magnets and higher magnet loadings. The current increases in proportion to the strength of the magnetic field generated by the micro- magnets. The current increases in proportion to the magnetic properties of the electroactive species. Entropy is reduced by incorporation of micro-magnets. These observations allow the development of theory and the more efficient design of better technologies for electrochemical energy storage and generation. Funding provided by this grant has yielded numerous patent applications and contributed to support six doctoral dissertations and one master's thesis. Students trained on this grant have evolved other electrochemical projects that have potential to improve power sources and advanced theory electrochemistry.

Agency
National Science Foundation (NSF)
Institute
Division of Chemistry (CHE)
Application #
0809745
Program Officer
Zeev Rosenzweig
Project Start
Project End
Budget Start
2008-07-15
Budget End
2011-06-30
Support Year
Fiscal Year
2008
Total Cost
$480,001
Indirect Cost
Name
University of Iowa
Department
Type
DUNS #
City
Iowa City
State
IA
Country
United States
Zip Code
52242