Electrohydrodynamic impedance in the presence of nonuniform transport properties

A numerical model is described for electrohydrodynamic impedance spectrosco py (EHDIS) in the presence of viscosity and diffusivity gradients near the electrode. The viscosity is assumed to depend on the concentration of a dif fusion-limited reaction product raised to a power. An effective diffusion c oefficient measured from a Levich analysis is shown to approach the near-su rface value of the diffusion coefficient when the near-surface kinematic vi scosity is greater than in the bulk. Similarly, EHDIS measurements can lead to quick estimates of near-surface viscosity. The model is applied to inte rpret experimental data for the steady-state limiting current and electrohy drodynamic impedance of the zinc-KOH system. (C) 2001 The Electrochemical S ociety. All rights reserved.