Reference underpotential

Fig. 31. Work function change, referred to the clean Pt electrode surface, as a function of electrode potential for Ag underpotential deposition onto Pt. The work function of bulk Cu would correspond... 

Surface limited reactions are well known in electrochemistry, and are generally referred to as underpotential deposits (UPD) [83-88], That is, in the deposition of one element on a second, frequently the first element will form an atomic layer at a potential under, or prior to, that needed to deposit the element on itself. One way of looking at UPD is that a surface compound, or alloy, is formed, and the shift in potential results from the free energy of formation of the surface compound. 

When a metal is in contact with its metal ion in solution, an equilibrium potential is established commonly referred to as Nernst potential (Er). Metal deposition occurs at potentials negative of Er, and dissolution for E > Er. However, when a metal is deposited onto a foreign metal substrate, which will always be the case for the initial stages of deposition, it is frequently observed that the first monolayer on the metal is deposited at potentials which are positive of the respective Nernst potential [37, 38]. This apparent violation for Nernst s law simply arises from the fact that the interaction between deposit metal and substrate is stronger than that between the atoms of the deposit. This effect has been termed underpotential deposition (upd), to contrast deposition processes at overpotentials. (One should keep in mind, however, that despite the symmetrical technical terms the physical origins of both effects are quite different. While the reason for an overpotential is solely due to kinetic hindrance of the deposition process, is that for underpotential deposition found in the energetics of the adatom-substrate interaction.)... 

Since a well-defined condition of the underpotential deposition metal at a definite coverage is better for studying its modified surface at a definite coverage, an irreversibly adsorbed underpotential deposition metal is desirable Sb on Pt(lll) for CO oxidation,Bi and Te on Pt(lOO) for formic acid oxidation, " Sb + Bi on Pt(lOO) for formic acid oxidation, and others found in these references. 

Scanning tunneling microscopy (STM), 787. 1157 bioelectrochemistry and, 1159 electrochemistry and. 1158 electrodeposition and. 1310 nanotechnology, 1345 piezoelectric crystal, 1158 tunneling current. 1157 underpotential deposition, 1313, 1315 Scavanger electrolysis, electrodeposition, 1343 Schlieren method, diffusion layer. 1235 Schmickler, 1495,1510 Schrodinger equation, 1456, 1490 Schultze 923,1497.1510 Screw dislocation, 1303, 1316, 1321, 1326 Secondary reference electrode, 815, 1109 Self-consumed electrode, 1040 Semiconductors... 

In this review, I have discussed some recent applications of computational ab initio quantum chemistry to electrochemistry. My selection of examples and references is incomplete and to some extent based on my personal involvement. For instance, 1 did not touch upon ab initio quantum-chemical calculations associated with the metal contribution to the double layer capacity,underpotential deposition phenomena,and the adsorption of fuel cell relevant molecules such as... 

All potentials references vs SCE. Underpotentials stated are vs the standard potential of —0.52 V... 

This chapter concerns the state of development of electrochemical atomic layer epitaxy (EC-ALE), the electrochemical analog of atomic layer epitaxy (ALE). EC-ALE is being developed as a methodology for the electrodeposition of compound semiconductors with nanoscale control. ALE is based on the formation of compounds, one monolayer (ML) at a time, using surface-limited reactions. An atomic layer of one element can be electrodeposited at a potential under that needed to deposit the element on itself, and this process is referred to as underpotential deposition (UPD). EC-ALE is the use of UPD for the surface-limited reactions in an ALE cycle. 

The major areas of application of reflectance spectroscopy have been the elucidation of reaction mechanisms, double layer studies, investigations of underpotential deposition (UPD), and studies of the electroreflectance effect (ER). This range is too large for an in depth discussion to be given here. Instead, two examples of the type of information that can be obtained will be described (a third system, hydrogen adsorption on platinum, has been discussed in Chapter 7). Those readers interested in more details are referred to a recent review [1], and the literature cited therein. 

Electrochemical SLRs are referred to as underpotential deposition (UPD) [4], where an atomic layer of a first element deposits on a second, at a potential prior to (under) that needed to deposit the first element on itself. The term atomic layer refers to a deposit no more than one atom thick, with a coverage less than a monolayer (ML). A ML corresponds to the deposition of one atom for each surface atom. UPD results from a larger interaction energy between two elements than between the element and itself, resulting in a surface compound or alloy. 

Underpotential deposition (UPD) of foreign metal adatoms on platinum single crystals in different acid electrolytes occupies a special position in interfacial electrochemistry. Of various systems examined the underpotential deposition of Cu on a Pt(lll) surface has been of particular interest since the interpretation of the nature of the Pt(lll)-Cu-Anion structure have been the subject of considerable controversy. Overviews with some different perspectives can be find in the References. [J-I3]. 

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