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Overpotentials on various electrodes table
Table shows overpotential values on selected electrodes.

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Electrodes overpotential [V]

Electrode / secreted substanceAlZnCrFeCdNiSnPbBiCuAgHgPtC
H2 acid environment0.80.70.50.51.20.411.30.80.60.41.20.10.5
H2 alkaline environment0.40.4-0.2-0.40.80.90.5--1.30.1-
O2---0.250.40.1-0.3-0.20.4-0.40.3
Zn-0.2--0.55----0.4--0.5-
Cr--0.6-----------
Fe---0.6----------
Cd----0.2--0.35-0.35--0.35-
Co------------0.3-
Ni-----0.6-----0.6--
Sn------0.20.3-0.3----
Pb-------0.20.120.02----
Bi-------0.20.35-----
Cu--------0.2---0.3-
Ag----------0.2-0.8-

Some facts

  • Overpotential is a difference between the potential of the electrode polarized by the flow of electric current and its potential in the equilibrium state.
    η=EE0\eta = E - E_0
    where:
    • η\eta - overpotential of electrode,
    • EE - potential of the electrode in a polarized state,
    • E0E_0 - electrode potential in the equilibrium state.
  • Overpotential is the polarization measure of the electrode.
  • Overpotential is measured in volts (V).
  • The author of the overpotential concept is W.A. Caspari. This concept appeared for the first time in 1899.
  • The total overvoltage on the electrode consists of partial overvoltages:
    η=ηΩ+ηΩ+ηa+ηc\eta = \eta_\Omega + \eta'_\Omega + \eta_a + \eta_c
    where:
    • ηΩ\eta_\Omega - resistive overvoltage, related to the potential drop across the electrode-solution interface,
    • ηΩ\eta'_\Omega - pseudo-resistance overvoltage, associated with the resistance of the electrolyte layer separating the test electrode and the reference electrode,
    • ηa\eta_a - activation overvoltage, associated with an additional expenditure of electric potential to overcome the activation energy of the electrode reaction,
    • ηc\eta_c - concentration overvoltage, associated with additional electrical work associated with changes in concentrations of electroactive substances in the immediate vicinity of a polarized electrode.
  • Concentration overpotential can be calculated using Nernst equation:
    ηc=RTnFlnaea0\eta_c=\frac{RT}{nF}\ln \frac{a_e}{a_0}
    where:
    • aea_e – depolarizer activity at the surface of a polarized electrode,
    • a0a_0 – the activity of the depolarizer in a state of equilibrium,
    • nn – number of electrons transferred in the transition reaction,
    • RR – gas constant,
    • TT – absolute temperature in kelvins,
    • FF – Faraday's constant.

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