| Abstract
| - Mass transport at cylindrical and spherical microelectrodes involving diffusion and migration is analyzed bymeans of numerical simulation under transient conditions. The origin of the intrinsic difficulties encounteredduring the numerical solution of the diffusion−migrationequations using implicit finite differences are outlined,especially for the particular case when the number ofelectrons transferred equals the charge number of theelectroactive species. The numerical results for transientconditions have been compared to the general analyticalsolutions for the current enhancement or diminishmentdue to migration under steady- and quasi-steady-stateconditions at 1D geometry microelectrodes (Amatore, C.;Fosset, B.; Bartelt, J.; Deakin, M. R.; Wightman, R. M.J. Electroanal. Chem.1988, 256, 255−268). Thisyields that the analytical limiting currents are applicable,within experimental error, to the analysis of transientdiffusion−migration current responses at microelectrodesof cylindrical and spherical geometries except extremelyshort times after the application of the potential step, i.e.,when current measurements are anyway already corrupted by ohmic drop when the supporting electrolyteconcentration is low. Also, this confirms that the currentenhancements or diminishments due to migration areidentical for both electrode geometries when steady- orquasi-steady states are approached and do not drasticallydiffer even under transient regimes.
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