Surface studies electrode

Matsumoto H, Inukai J and Ito M 1994 Structures of copper and halides on Pt(111), Pt(IOO) and Au(111) electrode surfaces studied by in situ scanning tunneling microscopy J. Eiectroanai. Chem. 379 223-31... 

T. Arakawa, A. Saito, and J. Shiokawa, Surface study of a Ag electrode on a solid electrolyte used as oxygen sensor, Applications of Surface Science 16, 365-372 (1983). 

De Marco R, Pejcic B, Prince K, van Riessen A (2003) A multi-technique surface study of the mercury(ll) chalcogenide ion-selective electrode in saline media. Analyst 128 742-749 Pejcic B, De Marco R (2004) Characterization of an AgBr-Ag2S-As2S3-Hgl2ion-selective electrode membrane a X-ray photoelectron and impedance spectroscopy approach. Appl Surf Sci 228 378-400... 

A third way to increase both the active surface area and the number of oxygenated species at the electrode surface is to prepare alloy particles or deposits and then to dissolve the non-noble metal component. This technique, which is similar to that used to prepare Raney-type catalysts, yields very high surface area electrodes and hence some improvements in the electrocatalytic activities compared with those of pure platinum. However, it is always difficult to be sure whether the mechanism of enhancment of the activities is due to this effect or the possible presence of remaining traces of the dissolved metal. Results with PtyCr and PtSFe were encouraging, although the effect of iron is still under discussion. From studies in a recent work on the behavior of R-Fe particles for methanol electrooxidation, it was concluded that the electrocatalytic effect is due to the Fe alloyed to platinum. ... 

Surface studies are difficult in the case of many metal electrodes since their regions of ideal or perfect polarizability are very narrow that is, the potentials of anodic dissolution (or oxidation) of the metal and of cathodic hydrogen evolution are close... 

Until the advent of modem physical methods for surface studies and computer control of experiments, our knowledge of electrode processes was derived mostly from electrochemical measurements (Chapter 12). By clever use of these measurements, together with electrocapillary studies, it was possible to derive considerable information on processes in the inner Helmholtz plane. Other important tools were the use of radioactive isotopes to study adsorption processes and the derivation of mechanisms for hydrogen evolution from isotope separation factors. Early on, extensive use was made of optical microscopy and X-ray diffraction (XRD) in the study of electrocrystallization of metals. In the past 30 years enormous progress has been made in the development and application of new physical methods for study of electrode processes at the molecular and atomic level. 

SHG has been used to study electrode surface symmetry and order using an approach known as SH rotational anisotropy. A single-crystal electrode is rotated about its surface normal and the modulation of the SH intensity is measured as the angle (9) between the plane of incidence and a given crystal axis or direction. Figure 27.34 shows in situ SHG results for an Au(ll 1) electrode in 0.1 M NaC104 + 0.002 M NaBr, using a p-polarized beam. The results indicate the presence of two distinct onefold... 

Watanabe, S., Inukai, J. and Ito, M. (1993) Coverage and potential dependent CO adsorption on Pt(llll), (711) and (100) electrode surfaces studied by infrared reflection absorption spectroscopy. Surf. Sci., 293, 1-9. 

Bhzanac BB, Arenz M, Ross PN, Markovic NM. 2004b. Surface electrochemistry of CO on reconstructed gold single crystal surfaces studied by infrared reflection absorption spectroscopy and rotating disk electrode. J Am Chem Soc 126 10130-10141. 

KitamuraF, Takahashi M, Ito M. 1989. Carbon monoxide adsorption on platinum (111) singlecrystal electrode surface studied by infrared reflection - absorption spectroscoy. Surf Sci 223 493-508. 

Oda I, Inukai J, Ito M. 1993. Compression structures of carbon monoxide on a Pt(lll) electrode surface studied by in situ scanning tunnehng microscopy. Chem Phys Lett 203 99 103. 

As mentioned above, the methods based on detection of electrons or ions or probing the electrode surface by these particles are generally handicapped by the necessity to move the studied electrode into vacuum, i.e. to work ex-situ. There are, however, two important exceptions to this rule electrochemical mass spectrometry and electrochemical scanning tunnelling microscopy. 

In the frequency region where the i/(0H) vibrations of interfacial H20 are observed, the normal Raman scattering from the bulk solution can obscure the SERS of interfacial H20 if appropriate precautions are not taken. In the studies reported here, the SERS of interfacial H20 was acquired with the electrode surface positioned as close to the electrochemical cell window as possible to minimize contributions from the bulk solution. When altering the electrode potential to deposit Pb onto the Ag electrode surface, the electrode was pulled away from the window several mm, the surface allowed to equilibrate at the new conditions, and the electrode repositioned near the cell window for spectral acquisition. 

In a PEMFC, the power density and efficiency are limited by three major factors (1) the ohmic overpotential mainly due to the membrane resistance, (2) the activation overpotential due to slow oxygen reduchon reaction at the electrode/membrane interface, and (3) the concentration overpotential due to mass-transport limitations of oxygen to the electrode surfaced Studies of the solubility and concentration of oxygen in different perfluorinated membrane materials show that the oxygen solubility is enhanced in the fluorocarbon (hydrophobic)-rich zones and hence increases with the hydrophobicity of the membrane. The diffusion coefficient is directly related to the water content of the membrane and is thereby enhanced in membranes containing high water content the result indicates that the aqueous phase is predominantly involved in the diffusion pathway. ... 

Double-layer properties in aqueous, propylene carbonate and formamide solutions have been studied at room temperature for liquid Ga-Pb alloy (0.06 atom % of Pb) [15], as a model of Pb electrode with renewable surface. The electrode behaves as an ideally polarizable electrode in a wide potential range, and its capacitance is intermediate between that of Ga and Hg electrodes and is independent of the solvent. This electrode is much less lipophilic than Ga. Adsorption of anions on this electrode increases in the sequence -BP4 = S042 < Gl < Br < r. 

Bare Ag electrodes. It is noteworthy that the recently studied electrode processes of organic compounds at pc-Ag electrodes involve mainly biochemically important species. For example, Zeng et al. [278] have investigated the voltammetric behavior of 2-mercaptopyrimidine (MPD) and have found that at appropriate potentials, MPD adsorbs on and interacts with the electrode to form an insoluble silver salt at the surface. The first of two cathodic... 

Uozumi, lizuka, and coauthors have published several studies on the electrochemical behavior of Pu at liquid cadmium cathodes in LiCl—KCl eutectic melts [128-130]. In one account [130] the authors studied the reduction of Pu " " to Pu° at the LiCl— KCl melt and liquid Cd interface and compared the results to those obtained at a solid Mo cathode surface. The electrode reaction at liquid Cd was found to be close to fully reversible with rapid. 

The ILs interact with surfaces and electrodes [23-25], and many more studies have been done that what we can cite. As one example, in situ Fourier-transform infrared reflection absorption spectroscopy (FT-IRAS) has been utilized to study the molecular structure of the electrified interphase between a l-ethyl-3-methylimidazolium tetrafluoroborate [C2Qlm][BF4] liquid and gold substrates [26]. Similar results have been obtained by surface-enhanced Raman scattering (SERS) for [C4Cilm][PFg] adsorbed on silver [24,27] and quartz [28]. 

The ultimate case of a changing surface in electrode kinetics is that of the deposition of one metal on another where the surface changes intrinsically. The study of such systems involves processes described under the title of underpotential deposition (Section 7.12.11). 

While considering trends in further investigations, one has to pay special attention to the effect of electroreflection. So far, this effect has been used to obtain information on the structure of the near-the-surface region of a semiconductor, but the electroreflection method makes it possible, in principle, to study electrode reactions, adsorption, and the properties of thin surface layers. Let us note in this respect an important role of objects with semiconducting properties for electrochemistry and photoelectrochemistry as a whole. Here we mean oxide and other films, polylayers of adsorbed organic substances, and other materials on the surface of metallic electrodes. Anomalies in the electrochemical behavior of such systems are frequently explained by their semiconductor nature. Yet, there is a barrier between electrochemistry and photoelectrochemistry of crystalline semiconductors with electronic conductivity, on the one hand, and electrochemistry of oxide films, which usually are amorphous and have appreciable ionic conductivity, on the other hand. To overcome this barrier is the task of further investigations. 

A rotating disk electrode (RDE) [7] is used to study electrode reactions, because the mass transfer to and from the electrode can be treated theoretically by hydrodynamics. At the RDE, the solution flows toward the electrode surface as shown in Fig. 5.22, bringing the substances dissolved in it. The current-potential curve at the RDE is S-shaped and has a potential-independent limiting current region, as in Fig. 5.6. The limiting current (A) is expressed by Eq. (5.33), if it is controlled by mass transfer ... 

It should be noticed that, in studying electrode kinetics, it is desirable to have a microscopic homogeneous current distribution (spatial distribution) at the electrode surface which is not always experimentally possible as will be discussed in Chap. 2. 

Spectroelectrochemical measurements can be made at conventional nontransparent electrodes by specular reflectance [23-25]. The optical beam is passed through the electrolyte and reflected from the electrode surface as shown in Figure 3.7C. This technique has been used effectively to study electrode mechanisms and to observe changes in the electrode surface itself. 

As shown above, most of the work to date on SH studies of electrode surfaces has been on noble metals. This is not to suggest that the technique is restricted to these surfaces alone. In fact a wide variety of other metals and semiconductors produce measureable SH signals [163]. There have been a number of metallic single crystal surfaces studied in UHV including Ni(lll) [8, 164-166], Pt(lll) [8, 165], Rh(lll) [167-169], and, Al(lll) and (110) [170]. A few of these studies have involved rotation of the crystal surface about the surface normal [166]. Of pertinence to electrochemical studies, two recent papers have appeared, one on Pt (111) [171] and the other on Fe(l 10) [172]. Both have involved measuring the rotational anisotropy from the metal surface. 

Liquid-solid mass transfer has also been studied, on a limited basis. Application to systems with catalytic surfaces or electrodes would benefit from such studies. The theoretical equations have been proposed based on film-flow theory (32) and surface-renewal theory (39). Using an electrochemical cell with rotating screen disks, liquid-solid mass transfer was shown to increase with rotor speed and increased spacing between disks but to decrease with the addition of more disks (39). Water flow over naphthalene pellets provided 4-6 times higher volumetric mass transfer coefficients compared to gravity flow and similar superficial liquid velocities (17). 

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