Steady-state voltammetry with stationary disk millielectrodes in magnetic fields: Nonlinear dependence of the mass-transfer limited current on the electron balance of the faradaic process

Generally, faradaic current passing through an electrolytic cell placed in a magnetic field causes stirring of the electrolytic solution and current-v oltage characteristics similar to those obtained with rotating disk electro des. It is reported herein that the intensity of the hydrodynamic convectio n generated by conventional disk millielectrodes in magnetic fields is inti mately related to the nature of the faradaic process, and that the mass-tra nsfer limited current, i(1), is proportional to n(3/2) where n is the numbe r of electrons involved in the heterogeneous electron transfer. That findin g has been justified on the basis of a feedback mechanism that relies on th e dependence of the faradaic current on the hydrodynamic velocity profile w ithin the electrolytic conductor, and of the hydrodynamic velocity profile on the current. The implications of the nonlinear dependence of i(1) on n h ave been discussed in terms of a moving-boundnry diffusion-layer model whic h is introduced into digital simulations and reproduces the main features o f magnetic field voltammograms. Combination of the new findings with our pr evious results lends to the following expression for disk millielectrodes i n transverse magnetic fields at room temperature: i(1) = 4.31 x 10(2) n(3/2 ) F A(3/4) \B\(1/3) D v(-1/4) C-bulk(4/3), where A is the electrode area, F the Faraday constant, \B\ the magnetic field strength, D the diffusion coe fficient, C-bulk the bulk concentration of the redox-active species, v the kinematic viscosity of the electrolyte, and when the numerical constant has units of cm T-1/3 s(-1/4) mol(-1/3).