Glossary
313
zirconia, which is a oxide ion (O
2–
) conductor, is used to electrochemically
pump oxygen.
Electrode – A system consisting of an electronic conductor (metal, semiconductor,
electrode material) in contact with an electrolyte (aqueous, organic, molten
salt, ceramic, polymer) and that is the site an oxidation-reduction reaction.
An electrode can be at equilibrium or polarized. In the latter case, it carries a
current characterized by the sign in electrochemistry. If the current is positive,
the electrode hosts an oxidation reaction and constitutes the anode. If the
current is negative, it is the cathode and hosts a reduction reaction.
Electrode overpotential (see Polarization) – The potential difference between a polarized
electrode (i.e., one carrying a current) and its equilibrium potential. Contrary
to the polarization, an overpotential concerns a well-defined electrochemical
reaction. Its variation with current gives information about the type of reaction
occurring at the electrode (transfer, adsorption, diffusion, …).
Electrode polarization – Polarizing an electrode consists of imposing a potential E i
different from the equilibrium potential E i=0 . When polarized, the electrode
carries a current of the same sign as the polarization. Thus, a cathode always
carries a negative current whereas an anode always carries a positive current,
by convention. Often the notation Π is used to denote the potential difference
Π = E i − E i=0 . The polarization, unlike the overpotential, is defined independently of the nature and number of reactions at the electrode.
Electrolyte – An electrolyte is a condensed phase (liquid or solid) in which the
electric conductivity is exclusively due to ions (cations, anions). In a solid
electrolyte, the electric current is generally due to a single ionic species. For
example, the current in stabilized zirconia (YSZ) consists of migrating oxide
ions O
2–
.
Electroneutrality equation – Expresses the electric neutrality of a phase. In solid-state
electrochemistry, one must consider the effective charges and the charge of
the electronic species.
Electronic conductivity – This is the conductivity due to the electronic species
(electrons and holes) present in a material. We speak respectively of n-type
or p-type conductivity when the mobile species is the electron or the hole. In
metals, the electronic conductivity is a decreasing function of temperature. In
semiconductors (electrode materials), electronic conductivity is an activated
phenomenon.
Equilibrium exchange current (density of) – Consider an electrode that hosts an equilibrium reaction
Ox + ne m Red
313
zirconia, which is a oxide ion (O
2–
) conductor, is used to electrochemically
pump oxygen.
Electrode – A system consisting of an electronic conductor (metal, semiconductor,
electrode material) in contact with an electrolyte (aqueous, organic, molten
salt, ceramic, polymer) and that is the site an oxidation-reduction reaction.
An electrode can be at equilibrium or polarized. In the latter case, it carries a
current characterized by the sign in electrochemistry. If the current is positive,
the electrode hosts an oxidation reaction and constitutes the anode. If the
current is negative, it is the cathode and hosts a reduction reaction.
Electrode overpotential (see Polarization) – The potential difference between a polarized
electrode (i.e., one carrying a current) and its equilibrium potential. Contrary
to the polarization, an overpotential concerns a well-defined electrochemical
reaction. Its variation with current gives information about the type of reaction
occurring at the electrode (transfer, adsorption, diffusion, …).
Electrode polarization – Polarizing an electrode consists of imposing a potential E i
different from the equilibrium potential E i=0 . When polarized, the electrode
carries a current of the same sign as the polarization. Thus, a cathode always
carries a negative current whereas an anode always carries a positive current,
by convention. Often the notation Π is used to denote the potential difference
Π = E i − E i=0 . The polarization, unlike the overpotential, is defined independently of the nature and number of reactions at the electrode.
Electrolyte – An electrolyte is a condensed phase (liquid or solid) in which the
electric conductivity is exclusively due to ions (cations, anions). In a solid
electrolyte, the electric current is generally due to a single ionic species. For
example, the current in stabilized zirconia (YSZ) consists of migrating oxide
ions O
2–
.
Electroneutrality equation – Expresses the electric neutrality of a phase. In solid-state
electrochemistry, one must consider the effective charges and the charge of
the electronic species.
Electronic conductivity – This is the conductivity due to the electronic species
(electrons and holes) present in a material. We speak respectively of n-type
or p-type conductivity when the mobile species is the electron or the hole. In
metals, the electronic conductivity is a decreasing function of temperature. In
semiconductors (electrode materials), electronic conductivity is an activated
phenomenon.
Equilibrium exchange current (density of) – Consider an electrode that hosts an equilibrium reaction
Ox + ne m Red