Cyclic Voltammetry

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Cyclic Voltammetry
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Current-Potential-Time Space
Time
Reversible System
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A New Waveform
Potential waveform
E?
Ei
0 ?
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Diffusion Condition
For the reversible case have the standard
Semi-infinite diffusion conditions plus
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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).
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Problem
There is no analytical solution to Ficks 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)
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Reversible CV Continued
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Dont Miss this Table
Myth A reversible wave will have a 60mV peak to
peak separation.
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NS Diagnostics
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Two KEY Points

1. Should use all three diagnostics
2. MUST go over three orders in magnitude in scan
   rate to reliably use a diagnostic!

Implication A single CV scan doesnt tell you
much, dont over interpret it!
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The Baseline Issue

• Three solutions
• Guess
• Record i-t over i-V
• Nicholson

Nicholson, Anal. Chem. 38, 1406 (1966)
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More On Baselines
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Hydrazine (N2H4)Oxidation
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eg(s)
Bpy p
t2g
e
eg(s)
Bpy p
t2g
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An EC Mechanism
ClRe(CO)3phen in acetonitrile (CH3CN)
tetrabutylammonium perchlorate
Luong, Nadjo and Wrighton, JACS, 100, 5790 (1978)
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Charge Transfer Communication
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