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. According to the IUPAC definition,  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:

•  is the electrochemical potential of species i, J/mol
•  is the chemical potential of the species i, J/mol
•  is the valency (charge) of the ion i, dimensionless
•  is Faraday's Constant, C/mol
•  is the local electrostatic potential, V.

In the special case of an uncharged atom,  = 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.

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.