Nucleation underpotential deposition

When underpotential deposition adsorption/desorption takes place randomly at any substrate site M, the following random adsorptioncontrolling treatment is to be employed, and when the process is controlled by a two-dimensional nucleation-growth mechanism, the process analysis should be carried out according to Section ni.l.(b). 

A kinetic study of Cu underpotential deposition was carried out to determine if it is best described by adsorption processes or by nucleation processes. The nucleation growth process is classified into two categories instantaneous nucleation growth and progressive nucleation growth. In the case of instantaneous nucleation growth, where nucleation site formation is so fast that no other following nucleation sites are created, the number of nucleation sites N(t) is expressed as... 

The overpotential three-dimensional nucleation process is affected by the change of prepolarization potential in the underpotential deposition region of Pb on Ag. When A is low (potential is close to feq), the rate of the... 

So-called underpotential deposited species arise when an electrochemical reaction produces first, on a suitable substrate adsorbent metal, a two-dimensional array or in some cases two-dimensional domain structures (cf. Ref 100) at potentials lower than that for the thermodynamically reversible process of bulk crystal or gas formation of the same element. The latter often requires an overpotential for initial nucleation of the bulk phase. The thermodynamic condition for underpotential deposition is that the Gibbs energy for two-dimensional adatom chemisorption on an appropriate substrate must be more negative than that for the corresponding three-dimensional bulk-phase formation. Underpotential electrochemisorption processes commonly involve deposition of adatoms of metals, adatoms of H, and adspecies of OH and O. 

The first electrodeposition of aluminum from an ionic liquid was reported in 1994 by Carlin etal. [157], Two years later, Zhao et al. [158] smdied the aluminum deposition processes on tungsten electrodes in trimethylphenylanunonium chlo-ride/aluminum chloride with mole ratio 1 2. It was shown that the deposition of aluminum was instantaneous as a result of three-dimensional nucleation with hemispherical diffusion-controlled growth, underpotential deposition of aluminum, corresponding to several monolayers. Liao et al. investigated the constant current electrodeposition of bulk aluminum on copper substrates was in 1-methyl-... 

Mendoza-Huizar LH, Robles J, Palomar-Pardave M (2002) Nucleation and growth of cobalt onto different substrates Part I. Underpotential deposition onto a gold electrode. J Electroanal Chem 521 95-106. doi 10.1016/S0022-0728(02)00659-9... 

In deposition of a metal on another substrate, nucleation of the new crystal is the first step. If the interaction of the new phase with the substrate is weak, as is usual on semiconductors or metals covered by oxide layers, nucleation requires relatively large overvoltages. There are, however, cases in which the interaction of the deposited metal atoms with the substrate surface is stronger than with a surface of their own material. In such cases, deposition in the form of submonolayers and full monolayers occurs already at potentials more positive than the equilibrium potential for the ion exchange on their own solid phase. This is the so-called underpotential deposition. ... 

Many ordered surface phases were found on electrodes by electrolytic metal deposition at underpotentials, often having different stractures than those observed by deposition from the gas phase. The reason is that the interactions of the substrate and the deposits with components of the electrolyte influence the forces of interaction between deposited atoms. This is demonstrated particularly well by the influence of anion adsorption on the potential and structure of underpotentially deposited metals. The stracture of the full monolayer is in some cases different from the bulk phase of the deposited metal. The monolayer stracture can be controlled by the stracture of the substrate, and such differences can extend even to the second layer. Three-dimensional nucleation, however, seems to play a minor role in the growth of the bulk phase on foreign substrates when imderpotential deposition takes place. ... 

There are not many experiments at open cells with small T variations which are directed to determination of fundamental kinetic quantities like transfer coefficients of homogeneous redox couples [67], heterogeneous rate constant of the charge transfer [68], or nucleation at solid electrodes [21] system described in [21, 69], deposition of lead at the boron-doped diammid electrode, is a good example for a possible new role of thermoelectrochemistry which could provide important information about the nucleation process at non-metaUic electrodes without underpotential deposition. The temperature dependence of this t)q)e of nucleation has been studied, yet only scarcely. 

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