Absolute electrode potential

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Absolute electrode potential, in electrochemistry, is the difference in electronic energy between a point inside the metal (Fermi level) of an electrode and a point outside the electrolyte in which the electrode is submerged.^[1]

According to an IUPAC definition, the absolute electrode potential is the electrode potential of a metal measured with respect to a universal reference system (without any additional metal-solution interface).^[2]

This potential is difficult to determine accurately. For this reason, standard hydrogen electrode is typically used for reference potential. The absolute potential of the SHE is 4.44 ± 0.02 V at 25 °C. Therefore, for any electrode

E M (a b s) = E M (S H E) + 4.44

where:

E is electrode potential, V

M denotes the electrode made of metal M

(abs) denotes the absolute potential

(SHE) denotes the electrode potential relative to the standard hydrogen electrode.

[edit] Determination

The basis for determination of the absolute electrode potential is given by the equation:

$E^M(abs) = \phi^M + \Delta ^M_S \psi$

where:

E^M(abs) is the absolute potential of the electrode made of metal M, V

φ M

is the electron work function of metal M, V

$\Delta ^M_S \psi$ is the contact (Volta) potential difference at the metal(M)-solution(S) interface, V.

For practical purposes, the value of the absolute electrode potential of the standard hydrogen electrode is best determined with the utility of data for an ideally-polarizable mercury (Hg) electrode:

$E^\ominus (H^+/H_2)(abs) = \phi^{Hg} + \Delta ^{Hg} _S \psi^\ominus_{\sigma=0} - E^{Hg}_{\sigma=0}(SHE)$

where:

$E^\ominus (H^+/H_2)(abs)$ is the absolute standard potential of the hydrogen electrode

σ=0 denotes the condition of the point of zero charge at the interface.

[edit] See also

[edit] References

^ Sergio Trasatti, "The Absolute Electrode Potential: an Explanatory Note (Recommendations 1986)", International Union of Pure and Applied Chemistry, Pure & AppL Chem., Vol. 58, No.7, pp. 955—966, 1986. http://www.iupac.org/publications/pac/1986/pdf/5807x0955.pdf (pdf)
^ IUPAC Gold Book - absolute electrode potential