Notions of Magnetoelectrocatalysis

Greater efficiency in reactions important to energy generation and storage has broad consequences beyond chemistry.  Means to enhance reaction rates are typically by chemical manipulation of catalyst materials, but physical manipulation of reactions, as by temperature and pressure, is also effective.  Here, means to increase reaction rates with magnetic fields and based on the magnetic properties of substrates and materials is considered.

For a wide range of reactions and device relevant to electrochemical energy and power, introduction of magnetic microparticles onto or into an electrode structure has been found to increase rates and to reduce the tax of overpotential^1-18. This includes batteries^3-6, fuel cells^7-11, photoelectrochemical cells¹, dye sensitized solar cells¹³, asymmetric supercapacitors¹³, hydride storage¹⁵, and alcohol electrolysis^13,14. Relevant reactions include hydrogen evolution reaction (HER)¹, hydride storage¹⁵, and CO oxidation⁸.

The basic notion is that electrons have properties of mass, charge, and spin. Spin interacts with the applied magnetic fields. To transfer an electron, it is necessary to transfer the spin and the charge. Application of a magnetic field should impact the rates of electron transfer. Experiments^1-17 have shown that the rate of the reaction depends on the magnetic properties of the reactants and products as well as the strength of the applied magnetic field H or intensity B. Measured rates are highly correlated² with the Zeeman energies in the system, Z = gSBb.

Detailed temperature studies for academically interested redox probes has allowed development of a model for magnetic effects on self exchange reactions¹. The model modifies Marcus theory to allow split of the energy levels by the applied field, which has several impacts on rate. The only specific chemical information in Marcus theory is the size and charge of the redox probe and the dielectric constant of the medium.  Consideration of the magnetic effects introduces additional magnetic properties into the model.

Here, several important energy relevant reactions are considered in light of the model. This includes the HER on several electrodes¹, hydride storage in Pd¹⁵, and diffusion limited CO oxidation on Pt⁸.   The impacts of the magnetic properties of the reactants and environment are discussed.

References

1. Lee, H. C. Magnetic Field Effects on Photoelectrochemical Hydrogen Evolution, Heterogeneous and Self Exchange Reactions. Ph.D., University of Iowa (2011).
2. Minteer, S. D. Magnetic Field Effects on Electron Transfer Reactions. Ph.D., University of Iowa (2000).
3. Zou, P. & Leddy, J. Electrochemical and Solid-State Letters 9, A43-A45 (2006).
4. Zou, P. Magnetic Field Effects on Nickel Electrodes for Nickel Metal Hydride Batteries. M.S., University of Iowa (2002).
5. Tesene, J. P. Magnetically-Treated Electrolytic Manganese Dioxide in Alkaline Electrolyte. M.S., University of Iowa (2005).
6. Motsegood, P. N. Improved Performance of Alkaline Batteries via Magnetic Modification and Voltammetric Detection of Breath Acetone at Platinum Electrodes. Ph.D., University of Iowa (2012).
7. Dunwoody, D. C., Ünlü, M., Wolf, A. K. H., Gellett, W.L. & Leddy, J. Electroanalysis 17, 1487-1494 (2005).
8. Gellett, W. L. Magnetic Microparticles on Electrodes: Polymer Electrolyte Membrane Fuel Cells, Carbon Monoxide Oxidation, and Transition Metal Complex Electrochemistry. Ph.D., University of Iowa (2004).
9. Dunwoody, D. C. Magnetically Modified Polymer Electrolyte Fuel Cells and Low Temperature Effects on Polymer Electrolyte Nafion. Ph.D., University of Iowa (2003).
10. Haverhals, L. Fuel Cells as Power Source and Sensors. Ph.D., University of Iowa (2008).
11. Ünlü, M. Coated Magnetic Particles in Electrochemical Systems: Synthesis, Modified Electrodes, Alkaline Batteries and Paste Electrodes. Ph.D., University of Iowa (2008).
12. Spolar, C. Electrochemical Studies of Ethanol and Related Compounds at Magnetically Modified Electrodes. M.S., University of Iowa (1999).
13. Lee, G. G., Leddy, J. & Minteer, S. D. Chem. Comm. 48, 11972-11974 (2012).
14. Lee, G. G. Magnetoelectrocatalysis: Enhanced Heterogeneous Electron Transfer Rates, Gratzel Cells, and MnO2 Electrodes. Ph.D., University of Iowa (2012).
15. Reed, J. J. Magnetic Effects on Hydride Storage in Palladium. M.S., University of Iowa (2012).
16. Zook, L. A. Morphological Modification of Nafion for Improved Electrochemical Flux. Ph.D., University of Iowa (1996).
17. Leddy, J., Amarasinghe, S., Zook, L. A. & Tinoco, F. in Proceedings of the 37th Power Sources Conference 93–95 (1996).
18. Leddy, J. & Coworkers, U.S. Patents (22) on Magnetically Modified Electrochemical Systems: 8,231,988 B, 8,227,134 B2, 7,842,178 B2, 7,709,115, 7,691,638, 7,585,543 B2, 7,041,401 B2, 6,949,179 B2, 6,890,670 B2, 6,514,575, 6,375,885 B1, 6,355,166 B1, 6,322,676 B1, 6,207,313 B1, 6,001,248, 5,981,095, 5,928,804, 5,871,625, 5,817,221, and 5,786,040.