| Abstract
| - Electrochemically generated magnetic forces at a disk-shaped ultramicroelectrode have beeninvestigated in large, nonuniform magnetic fields. Two sources of magnetic force are simultaneously operativein the electrochemical experiment, both having a significant influence on molecular transport of theelectrochemical reactants and products. First, the magnetohydrodynamic (MHD) force, FMHD, described bythe Lorentz equation, arises from the diffusionofelectrogeneratedions in the magnetic field. The magnitudeof FMHD is dependent upon the strength and orientation of the magnetic field. Second, the gradient magneticforce, F∇B, which is proportional to the gradient of the magnetic field, arises from electrogenerationofparamagneticmolecules in a nonuniform magnetic field. F∇B is dependent on the magnetic field strength, itsspatial gradient, and the magnetic properties of the redox-active molecules. F∇B and FMHD may be experimentallydecoupled and investigated by variation of the field homogeneity and the electrode orientation. Specifically,FMHD is negligibly small when the surface of the ultramicroelectrode is oriented perpendicular to the magneticfield, thus allowing F∇B to be investigated without interference from magnetohydrodynamic flows. Order-of-magnitude theoretical estimates of FMHD and F∇B are correlated with voltammetric data for the electrochemicalreduction of nitrobenzene at a 25-μm-radius Pt microdisk electrode in a superconducting cryomagnet.Enhancements in the voltammetric limiting current as large as ∼400% (B = 9.4 T, ∇B = 0 T/m) and ∼100%(B = 6 T, ∇B ∼ 75 T/m) are associated with FMHD and F∇B, respectively.
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