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Cyclic Voltammetry. Current-Potential-Time Space Reversible System Time.

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Presentation on theme: "Cyclic Voltammetry. Current-Potential-Time Space Reversible System Time."— Presentation transcript:

1 Cyclic Voltammetry

2 Current-Potential-Time Space Reversible System Time

3 Potential waveform: 0 EiEi E A New Waveform

4 For the reversible case have the standard Semi-infinite diffusion conditions plus: Diffusion Condition

5 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).

6 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)

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10 Reversible CV Continued

11 Myth: A reversible wave will have a 60mV peak to peak separation. Don’t Miss this Table

12 N&S Diagnostics

13 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 doesn’t tell you much, don’t over interpret it!

14 The Baseline Issue Nicholson, Anal. Chem. 38, 1406 (1966) Three solutions Guess Record i-t over i-V Nicholson:

15 More On Baselines

16 Hydrazine (N 2 H 4 )Oxidation

17 Bpy  * t 2g eg(*)eg(*) e–e– Bpy  * t 2g e g (  *)

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19 An EC Mechanism ClRe(CO) 3 phen in acetonitrile (CH 3 CN) + tetrabutylammonium perchlorate Luong, Nadjo and Wrighton, JACS, 100, 5790 (1978)

20 Charge Transfer Communication

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