5. A review of Voltammetry fundamentals#

Much of this section is paraphrased from David Harvey’s Analytical Chemistry 2.1 text which can be accessed via Libre Text.

See also

Be sure to check out section 11.1 of Harvey’s book for a refresher on these topics.

Electrochemical techniques rely on the measurement of potential and current in order to understand chemical phenomena such as reactivity and concentration. Most, but not all, electrochemical techniques involve the study of the movement of electrons in an oxidation-reduction reaction. There are several important concepts in electrochemistry which are worth reviewing:

  1. we cannot control simultaneously current and potential

  2. the electrode’s potential determines the analyte’s form at the electrode’s surface

  3. the concentration of analyte at the electrode’s surface may not be the same as its concentration in bulk solution

  4. current is a measure of the rate of the analyte’s oxidation or reduction

  5. in addition to an oxidation-reduction reaction, the analyte may participate in other chemical reactions

Let’s discuss how these five concepts are incorporated into voltammetry. The first item suggests that we must choose whether to control potential or current. As the name suggests, we measure the current (-ammetry) as a function of potential in a voltammetric measurement. Because we control the potential, we control what is happening at the electrode surface. We can adjust the potential to force a species in solution 1 to become oxidized or reduced by adjusting the potential relative to the reduction potential of the solute. Note that we only have control of what happens at the electrode/electrolyte interface. The bulk of the solution is unaffected unless we have specifically designed the experiment to influence the entire solution. The fact that electrochemical reactions are happening heterogeneously in the solution has a significant impact on the relationships between current and potential that we will observe. The last two points are what make voltammetry interesting. Since current is a measure of the flow of electrons, more electron flow indicates that more oxidation or reduction (collectively, electrolysis) is happening. Therefore, the magnitude of the current informs us about the rate of a reaction. Lastly, we can use voltammetry to explore what - if anything - a molecule does before or after electrolysis.

Footnotes

1

technically, or adsorbed onto the electrode surface, but we won’t deal with adsorbed species here.

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