Question 1

What is overpotential in electrochemistry?

Accepted Answer

Overpotential (η) is the extra voltage applied beyond the thermodynamic equilibrium potential needed to drive a net electrochemical reaction. A positive overpotential drives oxidation (anodic current); a negative overpotential drives reduction (cathodic current). Overpotential accounts for kinetic barriers and is a major source of energy loss in batteries and electrolyzers.

Question 2

What does the exchange current density represent?

Accepted Answer

Exchange current density i₀ is the magnitude of the anodic and cathodic currents flowing at equilibrium, where they exactly cancel. A high i₀ means the electrode reaction is fast and reversible—small overpotentials produce large currents. A low i₀ indicates a sluggish reaction requiring larger overpotentials to drive significant current.

Question 3

What is a Tafel slope and why does it matter?

Accepted Answer

At large overpotentials, the Butler-Volmer equation simplifies so that log(current) varies linearly with overpotential—this is the Tafel region. The slope of this line (Tafel slope) equals 2.303RT/(αF) and reveals the transfer coefficient α and reaction mechanism. Experimentally measured Tafel slopes are used to identify rate-determining steps in multi-step electrode reactions.

⚡ Electrode Kinetics

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