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Chronoamperometry

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Chronoamperometry

Chronoamperometry is an electrochemical technique in which the potential of the working electrode is stepped and the resulting current from faradaic processes occurring at the electrode (caused by the potential step) is monitored as a function of time. Limited information about the identity of the electrolyzed species can be obtained from the ratio of the peak oxidation current versus the peak reduction current. However, as with all pulsed techniques, chronoamperometry generates high charging currents, which decay exponentially with time as any RC circuit. The Faradaic current--which is due to electron transfer events and is most often the current component of interest--decays as described in the Cottrell equation. In most electrochemical cells this decay is much slower than the charging decay--cells with no supporting electrolyte are notable exceptions. Most commonly investigated with a three electrode system. Since the current is integrated over relatively longer time intervals, chronoamperometry gives a better signal to noise ratio in comparison to other amperometric technique.

Example

Anthracene in deoxygenated dimethylformamide (DMF) will be reduced (An + e -> An) at the electrode surface that is at a certain negative potential. The reduction will be diffusion-limited, thereby causing the current to drop in time (proportional to the diffusion gradient that is formed by diffusion).

You can do this experiment several times increasing electrode potentials from low to high. (In between the experiments, the solution should be stirred.) When you measure the current i(t) at a certain fixed time point τ after applying the voltage, you will see that at a certain moment the current i(τ) does not rise anymore; you have reached the mass-transfer-limited region. This means that anthracene arrives as fast as diffusion can bring it to the electrode.

References

Chronoamperometry Wikipedia


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