Magnetic Fields That Enhance the Rates of Multistep Reactions Important in Energy Storage and Conversion

Thursday, October 15, 2015: 11:50
104-B (Phoenix Convention Center)
W. L. Gellett, H. C. Lee, J. J. Reed (University of Iowa), and J. Leddy (University of Iowa)
Reactions at the electrode solution interface are ubiquitous and integral in electrochemical generation and storage systems. As the number of steps in the electron transfer process increases, the probability of reduce energy efficiency increases through undesirable side reactions and slow steps. When the electron transfer step slows the overall reaction rate, electrocatalysts can increase net efficiency.
    Incorporation of magnetic microparticles to the electrode has been shown to increase the efficiency of various electrochemical energy systems that include fuel cells, batteries, photovoltaics, and supercapacitors. It is generally observed that energy and power are increased by 40 % on incorporation of magnetic microparticles.
    Every interfacial electron transfer process is composed of multiple steps. The simplest model is mass transport of the reactant to the electrode surface, the electron transfer, and mass transport of the product into the solution. In multistep processes, additional steps may be important such as adsorption, multiple electron transfers, and chemical reaction on the surface or in the bulk. The electron transfer step is usually envisioned as a simple charge transfer. However, the electron transfer includes transfer of charge and spin. Magnetic properties of the electron and molecular entities arise through the spin. Addition of magnetic microparticles alters the rates of interfacial electron transfers.
    Here, three examples of magnetoelectrocatalysis in reactions important to electrochemical generation and storage are presented. In each of these systems, chemically inert micromagnets are held to the electrode surface in a coating of Nafion (R). In these reactions, there are components of mass transport, adsorption, interfacial spin and charge transfer, and surface reactions.
  • The hydrogen evolution reaction (HER) is facilitated at magnetically modified, single crystal p-Si. Overpotential is reduced >500 mV on magnetic modification.
  • Hydride storage in palladium is improved as the interfacial rates of H∙ transfer are increased by several orders of magnitude and overpotentials reduced by several hundred millivolts.
  • CO oxidation on platinum occurs near the thermodynamic potential at room temperature in water. The overpotential is reduced 600 mV with micromagnets.

    In each of these technologically important reactions, magnetic microparticles increase the rates of inherently slow, interfacial reactions. The effect is a physical interaction wherein magnetoelectrocatalysis effects substantially increased rates of electron transfer.