Electrochemistry with Stationary Disk and Ring−Disk Millielectrodes in Magnetic Fields

The most well-known effect of the magnetic field on electrochemical systems is hydrodynamic convection (stirring) of the electrolytic solution. The basic hydrodynamic equations governing mass transport under the magnetic force are well-understood. However, owing to the nonlinear character of those equations and the fact that neither the velocity nor the concentration profile near the electrode is known a priori, rigorous analytical solutions are not available. Retreating to a semiempirical treatment of mass transport, we took the approach of letting the rigorous hydrodynamic equations guide us to the system parameters that should control the steady-state mass-transport-limited current, and subsequently to vary all those parameters systematically using conventional millimeter-sized disk electrodes, and a range of compounds and solvents. To our knowledge, this study comprises the first of its kind, and we concluded that the limiting current i l = 4.31 × 10 3 n f +1 F A 3/4 B 1/3 D ν -1/4 C bulk 4/3, where n is the number of electrons involved in the redox process, F is the Faraday constant, A is the electrode area, B is the magnetic field strength, D is the diffusion coefficient, C bulk is the bulk concentration of the redox-active species, ν is the kinematic viscosity of the electrolyte, and f > 0. The angular flow profile near the electrode surface was mapped using an electrochemical generation/collection method.