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Cyclic Voltammetry. Current-Potential-Time Space. Time. Reversible System. A New Waveform. Potential waveform: . E . E i. 0  . Diffusion Condition. For the reversible case have the standard Semi-infinite diffusion conditions plus:. Solution. 1948

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Presentation Transcript
current potential time space
Current-Potential-Time Space

Time

Reversible System

a new waveform
A New Waveform

Potential waveform:

E

Ei

0 

diffusion condition
Diffusion Condition

For the reversible case have the standard

Semi-infinite diffusion conditions plus:

solution
Solution

1948

Sevick, “Oscillographic Polarography with Periodic Triangular Voltage”, Collection of Czech. Chem. Comm., 13, 349 (1948).

Randles, “A Cathode Ray Polarograph”, Faraday Society, 44, 327 (1948).

problem
Problem

There is no analytical solution to Fick’s second law when the boundary is time dependent. Sevick and Randles solutions was to approximate the integral with a series. While this works for the reversible case, it is not very pragmatic for more complex mechanisms.

New Solution:

Wait for a high speed computer (IBM main frame -1964- University of Wisconsin at Madison)

Nicholson and Shain, “Theory of Stationary Electrode Polarography”, Analytical Chemistry, 36, 706 (1964)

don t miss this table
Don’t Miss this Table

Myth: A reversible wave will have a 60mV peak to peak separation.

two key points
Two KEY Points

Should use all three diagnostics

MUST go over three orders in magnitude in scan rate to reliably use a diagnostic!

Implication: A single CV scan doesn’t tell you much, don’t over interpret it!

the baseline issue
The Baseline Issue
  • Three solutions
  • Guess
  • Record i-t over i-V
  • Nicholson:

Nicholson, Anal. Chem. 38, 1406 (1966)

slide17

eg(s*)

Bpy p*

t2g

e–

eg(s*)

Bpy p*

t2g

an ec mechanism
An EC Mechanism

ClRe(CO)3phen in acetonitrile (CH3CN) + tetrabutylammonium perchlorate

Luong, Nadjo and Wrighton, JACS, 100, 5790 (1978)