Natural Convection at Microelectrodes

摘要

Steady-state voltammetric currents for Fe(CN)6(-4) oxidation and Fe(CN)6(-3)reduction in 0.2 M KCl solutions are shown to be a function of the orientation of Au and Pt microdisk electrodes (radius = 6.4 to 25 micrometers) with respect to the gravitational field. The observed angular dependencies for the Fe(CN)6(-3/-4) couple are in agreement with theoretical expectations based on electrochemically-generated fluid density gradients within the depletion layer. The results demonstrate that steady-state voltammetric currents measured at microelectrodes are comprised of both diffusional and natural convection mass-transfer fluxes. At 25 micrometers-radius microdisks, natural convection accounts for between 2 and 13% of the total current for redox concentrations between 10 and 500 mM, respectively. The contribution of mass-transfer due to natural convection is shown to rapidly decrease with decreasing electrode size. jg.