Diffusion Impedance in a Thin Layer Cell

In electrochemistry, a thin layer cell is a device used to perform analytical microanalysis within a thin electrolyte layer. This Demonstration shows the electrochemical diffusion impedance in a thin layer cell. On the left, the configuration of a thin layer cell is shown; the blue plate is the large working electrode, separated from the insulating substrate (green plate) by a distance (m). On the right, the electrochemical impedance is shown in a Nyquist diagram.


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For a thin layer cell of thickness and the insulating substrate (a boundary impermeable to the diffusing species at the substrate), the diffusion impedance is given [1]:
is the frequency of the impedance perturbation,
is the scaling factor,
is the electrolyte film thickness,
is the diffusion coefficient,
is the imaginary unit.
This Demonstration shows that when the electrolyte film thickness is larger than about 100 m, the diffusional impedance behaves like a Warburg impedance (Snapshot 4). For smaller , however, the impedance at high frequency maintains Warburg behavior, but at low frequencies, it changes to resemble a capacitive impedance (Snapshots 1–3).
[1] T. Jacobsen and K. West, "Diffusion Impedance in Planar, Cylindrical and Spherical Symmetry," Electrochimica Acta, 40, 1995 pp. 255–262.
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