Underpotential deposition of metals

Huckaby D A and Blum L 1991 A model for sequential first-order phase transitions occuring in the underpotential deposition of metals J. Eiectroanai. Chem. 315 255-61... 

Hydrogen adsorption from solution Oxygen adsorption from solution Underpotential deposition of metals Adsorption of probe molecules from solution ... 

These primary electrochemical steps may take place at values of potential below the eqnilibrinm potential of the basic reaction. Thns, in a solntion not yet satnrated with dissolved hydrogen, hydrogen molecnles can form even at potentials more positive than the eqnilibrinm potential of the hydrogen electrode at 1 atm of hydrogen pressnre. Becanse of their energy of chemical interaction with the snbstrate, metal adatoms can be prodnced cathodically even at potentials more positive than the eqnilibrinm potential of a given metal-electrolyte system. This process is called the underpotential deposition of metals. 

Underpotential Deposition of Metal Atoms Because of the energy of interaction between a foreign substrate and the adsorbed metal atoms formed by discharge, cathodic discharge of a limited amount of metal ions producing adatoms is possible at potentials more positive than the equilibrium potential of the particular system, and also more positive than the potential of steady metal deposition. 

Electrodes modified by underpotential deposition of metal were subjected as electrocatalysts to reduction of oxygen,oxidation of formic acid, and other processes in which polycrystalline metal substrates were used (see review in Ref. 151). Electrocatalysis of single-crystal electrodes modified by underpotential deposition was also investigated, as reviewed by Ad2iC. ... 

SAMs controlling electrochemistry, whereas the reverse holds for the other one, both topics are inseparably intertwined as exemplified by the underpotential deposition of metal on SAM-modified electrodes where patterned SAMs allow localization of metal UPD, which in turn affects the monolayer. 

Underpotential deposition of metal adatoms at foreign metal electrodes shows a strong effect on the kinetics of inner sphere redox reactions such as the reduction of Cr(OH2)sCl2+ [130] due to electrostatic and specific interactions. 

Oxide electrodes have been observed to be almost immune from poisoning effects due to traces of metallic impurities in solution [99]. This is undoubtedly due primarily to the extended surface area. It can be anticipated that the calcination temperature must have a sizable effect. But in addition, a different mechanism of electrodeposition must be operative. Chemisorption on wet oxides is usually weak because metal cations are covered by OH groups [479]. As a consequence, underpotential deposition of metals is not observed on Ru02, although metal electrodeposition does takes place. However, electrodeposited metals give rise to clusters or islands and not to a monomolecular layer like on Pt. Therefore, the oxide active surface remains largely uncovered even if metallic impurities are deposited [168]. Thus, the weak tendency of oxides to adsorb ions, and its dependence on the pH of the solution is linked to their favorable behavior observed as cathodes in the presence of metallic impurities. 

Induced adsorption — Enhancement of the - adsorption of a component induced by another adsorbed species. These phenomena are treated in terms of induced anion and cation adsorption. Interrelation of anionic -> specific adsorption and -> underpotential deposition of metal ions is a typical example for the induced adsorption of anions [i]. 

The high mass sensitivity of ETSM sensors renders them particularly suited for the analysis of monolayer and submonolayer films. In fact, the earliest applications of the ETSM involved studying the electrochemical deposition of monolayers, including the formation of metal oxides [207], electrosorption of halides [208], and the underpotential deposition of metal atoms [209-213]. In some cases, the electrovalency (i.e., the ratio of moles of electrons transferred at the electrode to moles of adsorbate deposited) was found to vary with adsorbing species the adsorption of iodide onto gold, for example, occurs with complete charge transfer from the halide to the electrode, whereas the adsorption of bro-... 

Underpotential deposition of metals is a commonly observed phenomenon, which has been found to occur for dozens of metal couples in both aqueous and nonaqueous media. It is characterized by the distance between the peak potential observed during a slow cathodic sweep, and the reversible potential for deposition of the metal in the same solution. This potential difference has been related to the difference in the electronic work function of the two metals concerned, although this correlation does not always liold strictly. Much research has been devoted to the study of underpotential deposition of metals on single... 

A phenomenon similar to the underpotential deposition of metals is also observed in the study of the anodic oxidation of halides. In Fig. 81 we show the dependence of current on potential during an anodic potential sweep obtained on a platinum electrode in a nonaauenns mpdinm A current peak corresponding to the formation of atomic bromine on the surface is observed, about 0.4 V before the potential for formation of molecular bromine is reached. The two reactions considered ... 

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