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Cyclic Voltammetry: Reading a Voltammogram
What the peaks, currents and potential gaps in a cyclic voltammogram actually tell you about a redox couple.
What is being plotted
A cyclic voltammogram plots current (y-axis) against applied potential (x-axis) as the potential is swept linearly in one direction and then reversed, producing one anodic (oxidation) peak and one cathodic (reduction) peak for a simple reversible redox couple.
The key quantities examiners ask about
| Quantity | What it tells you |
|---|---|
| Epa, Epc (anodic/cathodic peak potentials) | Their average approximates the formal redox potential E°′ for a reversible couple |
| ΔEp (peak separation) | Close to 59/n mV at 25°C for an electrochemically reversible couple; a larger gap signals slower electron-transfer kinetics |
| ipa / ipc ratio | Close to 1 for a simple reversible couple with no follow-up chemistry consuming the product |
Reversible, quasi-reversible and irreversible behaviour
As electron-transfer kinetics slow down relative to the scan rate, the peak separation grows beyond the ideal 59/n mV and the curve becomes less symmetric — this is the quasi-reversible regime, shading into fully irreversible behaviour where only one clear peak may appear at all. For a diffusion-controlled reversible process, peak current follows the Randles-Sevcik relation: peak current is proportional to the square root of scan rate, with concentration, electrode area and the diffusion coefficient as the other factors.
Where this fits a physical chemistry prep plan
Cyclic voltammetry sits within the electrochemistry section of GATE Chemistry (CY) and CSIR-NET Part C, usually alongside Nernst-equation numericals and conductance-based questions.
FAQs
Is cyclic voltammetry tested quantitatively or mostly conceptually?
Both appear. Conceptual questions on reading peaks and reversibility are more common than full numerical Randles-Sevcik calculations, but the relation is still worth knowing qualitatively.
What does a large ΔEp indicate?
Slower electron-transfer kinetics at the electrode surface, moving the system from reversible toward quasi-reversible behaviour.
How does scan rate affect the voltammogram?
Peak current increases with the square root of scan rate for a diffusion-controlled reversible process, and peak separation can increase at higher scan rates for a quasi-reversible system.
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