Effect of Electrical Double Layer on Transport Limited Currents at Microelectrodes
Abstract
An analysis of transport of charged and uncharged species associated with a steady-state faradaic process at a spherical microelectrode is reported. Systems comprising various relative concentrations of a redox species are examined and, if charged, its counter ion, and an inert electrolyte. Of particular interest is the behavior of these systems when the thickness of the diffuse double layer (characterized by the Debye length, 1/kappa) and the radius of the electrode (r sub 0) are comparable. Transport of each species is assumed to be governed by the Nernst-Planck equation. A generalized solution obtained using finite-difference simulations demonstrates that significant enhancement or inhibition of the steady-state flux can occur and will depend upon the dimensionless parameter r sub 0 kappa, upon the relationship between the applied potential, the formal redox potential (Eo'), and the potential of zero charge, and upon the charges and relative concentrations of the species in solution. Analytic solutions for several limiting cases are discussed and serve as simple expositions of the phenomena as well as a verification of the simulations. In infinitely dilute ionic solutions, the limiting flux of ionic species may be computed directly from the Smoluchowski-Debye theory for ionic bimolecular reaction rates. Computation of theoretical voltammograms in the limit of infinite dilution reveals the surprising results that under certain reaction conditions the steady-state current-voltage curve will be peaked rather than sigmoidal giving the appearance that electrochemical activity occurs only within a small (several hundred millivolt) potential window.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 1989
- Accession Number
- ADA211586
Entities
People
- H. S. White
- J. D. Norton
- S. W. Feldberg
Organizations
- University of Minnesota