Electrochemical potential

In electrochemistry, the electrochemical potential, $$\bar{\mu}$$, sometimes confusingly abbreviated to ECP, is a thermodynamic measure that combines the concepts of energy stored in the form of chemical potential and electrostatics. It 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 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, 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


 * $$\bar{\mu}_i=\mu_i + z_iF\Phi$$,

where $$\mu_i$$ is the chemical potential, $$z_i$$ is the valency of the ion, $$F$$ is Faraday's constant, and $$\Phi$$ is electrostatic potential.

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 in the meaning of electrode potential (either of a corroding electrode, an electrode with a non-zero net reaction, or an electrode at equilibrium). Such a usage can lead to confusion. The measured electrode potential does not equal the change of the electrochemical potential (see Galvani potential). Therefore, the recent literature usually expands the abbreviation ECP as "electrochemical corrosion potential". For electrode at equilibrium, the phrase of equilibrium or reversible potential of the electrode is used.