Single-crystal metal electrodes

Adsorption studies of hydrogen on single-crystal metal electrode surfaces using advanced instrumental techniques... 

The macroscopic electrochemical experiments as well as the structural studies with molecular adlayers were performed on single crystal metal electrodes, such as Au hkl), Ag(hkl) and Cu(hkl). To describe our experimen-... 

Numerous studies employing both polycrystalline and single crystal metal electrodes and semiconductor surfaces have been reported for an overview, see [772]. The possible advantages of a simultaneous (double beam) application of electroreflectance spectroscopy and second harmonic generation have been pointed out [769]. 

Fig. 230 Schematic diagram of a set-up of optics for doublebeam UV-visible reflectance measurement at the two spots on a single facet of a small single crystal metal electrode.

Infrared spectroscopy is frequently applied to investigate CO adsorption on electrodes, because CO is important as an intermediate and surface poison in many electrocatalytic reactions and the C-O stretching vibrational modes of the adlayer are sensitive to the chemical environment at the metal/solution interface. Infrared spectra of CO adsorbed on low-index surface planes of Pt single-crystal electrodes have become a benchmark for use in understanding the behavior of CO on other surfaces. Related approaches have been extended to bulk single-crystal metal electrodes that include Pd [66, 67], Ir [68-71], Rh [13, 70], Ru [72-74], Ni [75, 76] and Au [77]. 

The following chapter is focused on the structure and phase behavior of specifically adsorbed anion adlayers on solid single-crystal metal electrodes. On the... 

Another important result from in situ STM imaging of adsorbed sulfate on M(lll), single-crystal metal electrodes is the observation of the adsorbate structure. It is found for Au(lll) [42], Pt(lll) [52], Rh(lll) [53], Ir(lll) [54], andCu(lll) [43] a /3 X V7 structure. This kind of information can be used in determining lateral... 

The adsorption of aliphatic alcohols, which adsorb on metals with the hydrocarbon tail facing the electrode surface, shows different patterns on real Ag crystal faces440,441 with respect to quasi-perfect single-crystal face electrodes.442-444 This specific point will be discussed in detail in Section III. 

The technology for making single crystal ball electrodes is inexpensive and well developed [223, 224], Wire of the noble metals Au and Pt can be melted in a hydrogen oxygen flame. By careful manipulation of the flame on the ball, it can be recrystallized repeatedly to form a perfect single crystal. The crystals have a set of flat spots, [111] planes, which develop on the surface. These facets feature some of the... 

Surface and Double-layer Properties Valette [19] has analyzed earlier experimental data on the inner-layer capacity at PZC for Ag(lll), Ag(lOO), and Ag(llO) surfaces in order to estimate the surface area and capacitance contributions of superficial defects for real electrodes, as compared to ideal faces. Considering the application of surface spectroscopy techniques to single-crystal Ag electrodes, one should note that anisotropy of the SHG response for metal electrode allows one to analyze and correlate its pattern with interfacial symmetries and its variations by changing nonlinear susceptibility and the surface structure. Early studies on Ag(lll) single-crystal electrodes have... 

Waszczuk et al. [329] have carried out radiometric studies of UPD of thallium on single-crystal Ag electrode from perchloric acid solutions. Deposition of Tl on Ag(lOO) to obtain monolayer, bilayer, and bulk crystallites has been studied by Wang et al. [330]. These studies have shown that apart from the substrate geometry, the nature of the substrate-adatom interactions also influence the structure of the UPD metal adlayers. This is because of the fact that, contrary to Au and Pt electrodes, Tl forms a well-ordered bilayer phase before bulk deposition on Ag(lOO) surface occurs. 

One should add that Abruna and coworkers have described UPD of Hg on various Au(h,k,l) electrodes in a review paper [28]. They have also studied UPD of other metals at various single-crystal metal surfaces. 

By running a potentiometric precipitation titration, we can determine both the compositions of the precipitate and its solubility product. Various cation- and anion-selective electrodes as well as metal (or metal amalgam) electrodes work as indicator electrodes. For example, Coetzee and Martin [23] determined the solubility products of metal fluorides in AN, using a fluoride ion-selective LaF3 single-crystal membrane electrode. Nakamura et al. [2] also determined the solubility product of sodium fluoride in AN and PC, using a fluoride ion-sensitive polymer membrane electrode, which was prepared by chemically bonding the phthalocyanin cobalt complex to polyacrylamide (PAA). The polymer membrane electrode was durable and responded in Nernstian ways to F and CN in solvents like AN and PC. 

The applications of inelastic tunneling presented in Sec. V point up both the strong and weak points of this spectroscopy. Inelastic electron tunneling is sensitive, has good resolution, does not require large capital investment, has a wide spectral range, is sensitive to all surface vibrations, and can be used on oxide and supported metal catalysts. However, a counter-electrode must be used, single crystal metal surfaces cannot be used, and spectra must be run at low temperatures. 

Activation (of noble metal electrodes) — Noble metal electrodes never work well without appropriate pretreatment. Polycrystalline electrodes are polished with diamond or alumina particles of size from 10 pm to a fraction of 1 pm to obtain the mirror-like surface. The suspensions of polishing microparticles are available in aqueous and oil media. The medium employed determines the final hydrophobicity of the electrode. The mechanical treatment is often followed by electrochemical cleaning. There is no common electrochemical procedure and hundreds of papers on the electrochemical activation of -> gold and platinum (- electrode materials) aimed at a particular problem have been published in the literature. Most often, -> cyclic and - square-wave voltammetry and a sequence of potential - pulses are used. For platinum electrodes, it is important that during this prepolarization step the electrode is covered consecutively by a layer of platinum oxide and a layer of adsorbed hydrogen. In the work with single-crystal (- monocrystal) electrodes the preliminary polishing of the surface can not be done. 

Spontaneous deposition of other metal nanoislands on Pt and Au single crystal substrates has also been reported. For instance, Os deposition on single crystal platinum electrodes was studied by both ex situ6,7,18 and in situ STM.19,20 In addition, in situ STM studies of the spontaneous depositions of Os,21,22 Pt23,24 and Sn25 on Au(lll) single crystal as well as Pt on Ru(0001)26 and Pb on Ru(0001)27 were also carried out. 

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