Tafelplots

Tafelplots are semi-log plots used in electrochemistry to analyze the kinetics of electrode reactions. They typically plot the overpotential η against the logarithm of the current density i (or current). In the kinetic region, where charge-transfer steps limit the rate rather than mass transport, the plot shows an approximate straight line, making it useful to extract kinetic parameters and compare catalysts or electrode processes.

The Tafel equation describes the relationship between overpotential and current in this region. It can be written as η = a + b log10(i), where a is an intercept that depends on the exchange current density i0, and b is the Tafel slope. The slope b is given by b = (2.303 RT)/(α n F) for a single-electron transfer with transfer coefficient α and n electrons involved in the rate-determining step. At a fixed temperature, this yields a typical value of about 0.0591 V per decade divided by αn. The intercept a relates to i0 through η = (2.303 RT)/(α n F) log10(i/i0).

Applications of Tafelplots include evaluating electrochemical kinetics, determining rate-determining steps, comparing catalytic activities, and assessing corrosion rates or fuel-cell/electrolysis performance. They are most reliable in the kinetic (activation-controlled) regime; deviations occur at high currents due to mass transport, concentration polarization, surface adsorption, or changes in mechanism. Temperature, electrode roughness, and solution conditions also affect the slope and intercept.