In electrochemistry, the electrochemical potential, 
, sometimes abbreviated to ECP, is a thermodynamic measure that combines the concepts of energy stored in the form of chemical potential and electrostatics.
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Conflicting terminologies
It is common in both solid-state physics and electrochemistry to discuss the chemical potential and electrochemical potential of an electron. However, in the two fields, the definitions of these two terms are swapped. In solid-state physics, the chemical potential of an electron is a synonym of Fermi level, and is constant across a device in equilibrium; while the electrochemical potential is equal to the chemical potential minus the local electric potential energy of an electron.[1] In electrochemistry, the electrochemical potential of an electron is a synonym of "Fermi level", and is constant across a device in equilibrium, while the chemical potential is equal to the electrochemical potential minus the local electric potential energy of an electron.[2]
Definition and usage
In generic terms, electrochemical potential is the mechanical work done in bringing 1 mole of an ion from a standard state to a specified concentration and electrical potential. By an IUPAC definition[3], it is the partial molar Gibbs energy of the substance at the specified electric potential, where the substance is in a specified phase. Electrochemical potential can be expressed as
,
where μi is the chemical potential, zi is the valency (charge) of the ion, F is Faraday's Constant, and Φ is electrostatic potential. In the special case of an uncharged atom, zi = 0 and so 
.
Electrochemical potential is important in biological processes that involve molecular diffusion across membranes, in electroanalytical chemistry, and industrial applications such as batteries and fuel cells. It represents one of the many interchangeable forms of potential energy through which energy may be conserved. Electrochemical potential is expressed in the unit of J/mol.
In cell membranes, the electrochemical potential is the sum of the chemical potential and the membrane potential.
Incorrect usage
The term electrochemical potential is sometimes used to mean an electrode potential (either of a corroding electrode, an electrode with a non-zero net reaction or current, or an electrode at equilibrium). This particular usage can lead to confusion. A measured electrode potential does not equal the change of the electrochemical potential (see Galvani potential). Therefore, the recent literature usually explains the abbreviation ECP as "electrochemical corrosion potential". For an electrode at equilibrium, the phrase equilibrium or reversible potential of the electrode is used.
See also
References
- ^ See, for example, Solid State Physics by Ashcroft and Mermin, page 593.
- ^ See, for example, Electrochemical Methods by Bard and Faulkner, 2nd edition, Section 2.2.4(a),4-5.
- ^ IUPAC Gold Book, http://goldbook.iupac.org/E01945.html
External links
Electrochemical potential - lecture notes from University of Illinois at Urbana-Champaign
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