Cyclic Voltammetry

Cyclic voltammetry sweeps the electrode potential linearly back and forth while recording current, producing a characteristic curve that reveals redox potentials, reversibility, and reaction mechanisms.

Definition

A potential-sweep voltammetric technique in which the electrode potential is cycled linearly between two limits while the resulting current is recorded as a function of potential.

Scope

This topic covers the cyclic voltammetry experiment: the triangular potential waveform, the origin and interpretation of anodic and cathodic peaks, peak separation and current ratios as diagnostics of reversibility, the scan-rate dependence described by the Randles–Ševčík relation, and the use of the technique to detect coupled chemical reactions. It is the most widely used method for initial electrochemical characterization.

Core questions

• How does sweeping the potential generate the characteristic peak-shaped current response?
• What do peak separation and the anodic-to-cathodic current ratio reveal about reversibility?
• How does peak current depend on scan rate, and what does this tell us about diffusion versus adsorption?
• How can coupled chemical reactions be diagnosed from changes in the voltammogram?

Key theories

Randles–Ševčík relation

For a diffusion-controlled reversible reaction the peak current is proportional to the square root of the scan rate and to bulk concentration, allowing concentration, diffusion coefficient, or electron count to be extracted.

Reversibility diagnostics

A reversible couple shows a peak separation near 59/n mV independent of scan rate and a near-unity peak-current ratio; deviations indicate slow electron transfer or coupled chemical steps.

Clinical relevance

Cyclic voltammetry is the standard first characterization for redox-active drugs, catalysts, battery materials, and biomolecules, used to determine formal potentials, screen electrocatalysts, evaluate electrode coatings, and study reaction mechanisms across chemistry and materials science.

History

The theory of peak-shaped sweep voltammetry was developed by Randles and Ševčík around 1948 and extended to a comprehensive diagnostic framework by Nicholson and Shain in 1964, after which cyclic voltammetry became the workhorse of mechanistic electrochemistry.

Key figures

• John E. B. Randles
• Augustin Ševčík
• Richard S. Nicholson
• Irving Shain

Seminal works

• nicholson1964
• bard2001
• elgrishi2018

Frequently asked questions

Why does peak current scale with the square root of scan rate?

For a diffusion-controlled reaction, faster sweeps thin the diffusion layer, steepening the concentration gradient and raising the flux; the square-root dependence is the signature distinguishing diffusing species from surface-adsorbed ones, which scale linearly.

What does a large peak separation indicate?

A peak separation well above 59/n mV, especially one that grows with scan rate, signals sluggish (quasi-reversible or irreversible) electron-transfer kinetics or uncompensated solution resistance rather than a fast reversible couple.