Underpotential deposition
Encyclopedia
Underpotential deposition (UPD) is a phenomenon of electrodeposition
of a species
(typically reduction of a metal
cation to a solid metal) at a potential
less negative than the equilibrium
(Nernst
) potential for the reduction of this metal.
The occurrence of underpotential deposition is often interpreted as a result of a strong interaction between the electrodepositing
metal M with the substrate S (of which the electrode
is built). The M-S interaction needs to be energetically favoured to the M-M interaction in the crystal lattice of the pure metal M. This mechanism is deduced from the observation that UPD typically occurs only up to a monolayer
of M (sometimes up to two monolayers). The electrodeposition of a metal on a substrate of the same metal occurs at an equilibrium potential, thus defining the reference point for the underpotential deposition. Underpotential deposition is much sharper on monocrystals than on polycrystalline
materials.
Electrodeposition
Electrodeposition may refer to:*Electroplating*Electrophoretic deposition*Underpotential deposition...
of a species
Chemical species
Chemical species are atoms, molecules, molecular fragments, ions, etc., being subjected to a chemical process or to a measurement. Generally, a chemical species can be defined as an ensemble of chemically identical molecular entities that can explore the same set of molecular energy levels on a...
(typically reduction of a metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
cation to a solid metal) at a potential
Potential
*In linguistics, the potential mood*The mathematical study of potentials is known as potential theory; it is the study of harmonic functions on manifolds...
less negative than the equilibrium
Equilibrium
Equilibrium is the condition of a system in which competing influences are balanced. The word may refer to:-Biology:* Equilibrioception, the sense of a balance present in human beings and other animals...
(Nernst
Nernst equation
In electrochemistry, the Nernst equation is an equation that can be used to determine the equilibrium reduction potential of a half-cell in an electrochemical cell. It can also be used to determine the total voltage for a full electrochemical cell...
) potential for the reduction of this metal.
The occurrence of underpotential deposition is often interpreted as a result of a strong interaction between the electrodepositing
Electrodeposition
Electrodeposition may refer to:*Electroplating*Electrophoretic deposition*Underpotential deposition...
metal M with the substrate S (of which the electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
is built). The M-S interaction needs to be energetically favoured to the M-M interaction in the crystal lattice of the pure metal M. This mechanism is deduced from the observation that UPD typically occurs only up to a monolayer
Monolayer
- Chemistry :A Langmuir monolayer or insoluble monolayer is a one-molecule thick layer of an insoluble organic material spread onto an aqueous subphase. Traditional compounds used to prepare Langmuir monolayers are amphiphilic materials that possess a hydrophilic headgroup and a hydrophobic tail...
of M (sometimes up to two monolayers). The electrodeposition of a metal on a substrate of the same metal occurs at an equilibrium potential, thus defining the reference point for the underpotential deposition. Underpotential deposition is much sharper on monocrystals than on polycrystalline
Polycrystalline
Polycrystalline materials are solids that are composed of many crystallites of varying size and orientation. The variation in direction can be random or directed, possibly due to growth and processing conditions. Fiber texture is an example of the latter.Almost all common metals, and many ceramics...
materials.