Halide underpotential deposition

Michaelis R, Zei MS, Zhai RS, Kolb DM (1992) The effect of halides on the structure of copper underpotential-deposited onto Pt(lll) a low-energy electron diffraction and X-ray photoelectron spectroscopy study. J Electroanal Chem 339 299-310... 

STM images of Ag underpotential deposition on Pt(lll) were observed as (1 X 1) and (VJx V3) structures at the potentials of Ag mono-layer formation and between two underpotential deposition peaks, respectively." The STM image at Pt(lOO) was examined for Cu underpotential deposition in the presence of halide ions in sulfuric acid solution... 

Metal ion and halide impurities are an issue in ionic liquids with discrete anions. As we have demonstrated in Chapter 11.5 Li+ (and K+) are common cationic impurities, especially in the bis(trifluoromethylsulfonyl)amides which typically contain 100 ppm of these ions from the metathesis reaction. Although Li and K are only electrodeposited in the bulk phase at electrode potentials close to the decomposition potential of the pyrrolidinium ions, there is evidence for the underpotential deposition of Li and K on gold and on other rather noble metals. For a technical process to deposit nickel or cobalt from ionic liquids the codeposition of Li and/or K, even in the underpotential deposition regime, has to be expected. 

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-... 

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 ... 

The adsorption of anions such as halides, cyanide, and sulfate/bisulfate on electrode surfaces is currently one of the most important subjects in electrochemistry [1 - 3]. It is well known that various electrochemical surface processes such as underpotential deposition of hydrogen and metal ions are strongly affected by co-adsorbed anions. Particularly, structures of the iodine adlayers on Pt, Rh, Pd, Au, and Ag surfaces have... 

Cathodic stripping analysis can also be carried out for species (usually anions) that deposit in an anodic preelectrolysis. For example, the halides (X ) can be determined at mercury by deposition as Hg2X2- Deposition on solid electrodes is also possible. In this case, surface problems (e.g., oxide films) and underpotential deposition effects often appear. On the other hand, the sensitivity for stripping from a solid electrode is very high, since the deposit can be removed completely, even at high scan rates. Stripping of films has often been used to determine the thickness of coatings (e.g., Sn on Cu) and oxide layers (e.g., CuO on Cu). ... 

Surface X-ray scattering (SXS) The first SXS study of an underpotentially deposited metal monolayer was reported more than ten years ago. In a recent review [132] it is demonstrated that this method is well suited for the study of the structure of metals, halides, and metal-halide adlayers on single-crystal electrodes. As another example, the study of the distribution of water at Ag(lll) surface can be mentioned [133]. 

In addition, the adsorption of halides from solution on metal surfaces can be thought of as UPD Cl [297], Br [298-300], and I [299,301-304], Normally, UPD is considered a precursor to the formation of a bulk deposit of an element. Bulk deposits of the halides are generally soluble, but the first atomic layer is formed at an underpotential. Recent studies have indicated that oxidative UPD of As can be performed as well [252,253]. 

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