Mono-metallic electrodes

Figure 5-11 shows a simple model of the compact double layer on metal electrodes. The electrode interface adsorbs water molecules to form the first mono-molecular adsorption layer about 0.2 nm thick next, the second adsorption layer is formed consisting of water molecules and hydrated ions these two layers constitute a compact electric double layer about 0.3 to 0.5 nm thick. Since adsorbed water molecules in the compact layer are partially bound with the electrode interface, the permittivity of the compact layer becomes smaller than that of free water molecules in aqueous solution, being in the range from 5 to 6 compared with 80 of bulk water in the relative scale of dielectric constant. In general, water molecules are adsorbed as monomers on the surface of metals on which the affinity for adsorption of water is great (e.g. d-metals) whereas, water molecules are adsorbed as clusters in addition to monomers on the surface of metals on which the affinity for adsorption of water is relatively small (e.g. sp-metals). 

Gold and mercury electrodes display ideally polarizable behavior in a broad range of electrode potentials. Under these conditions, the metal solution interface behaves as a capacitor. The capacity of the electrode decreases when organic molecules are present at the interface [28,29]. The measurement of the electrode capacity provides a convenient tool to study the spreading of an insoluble mono-layer onto a metal electrode surface. The capacity may be measured by applying a linear voltage sweep to the electrode and recording the voltammetric current (CV-cyclic... 

The modifleation of a metal electrode surface by the controlled deposition of a mono-layer of a second metal at potentials positive to the bulk deposition potential is known as underpotential deposition (upd) [22]. This area of research has proved to be especially... 

There are other evidences indicating that the quenching of PL is dominated by the dipole interactions due to the presence of the metal electrode and that the doping phenomenon only affects the first few mono layers of the polymer at the interface... 

Cmcentration Cell, which has mono-metaUic electrodes, but the anode is immersed in a concentrated region of the electrol) as shown in Figure 2.2c. This cell has the electrodes made of the same metal and it is similar to a galvartic with respect to the electrode polarity and current flow direction. The electrodes are immersed in a nonhomogeneous electrolyte, but the anode is within the concentrated portion of the electrolyte where the concentration of species j is Cj(anode) > Cj cathode). 

A hydrogen fuel cell known as a mono-skeleton catalyst (MSK) has demonstrated optimum cell performance. The cell was designed and developed by Brown, Bovary and Company of Switzerland around 1959. Swiss scientists have selected the best materials and technology for electrodes. The metal electrodes were selected to obtain an adequate storage capacity in case the cells were subjected to overloading for a long time. The materials selected for the electrodes offered optimum electrochemical properties. 

The micro structured platelets, hold in a non-conducting housing, were realized by etching of metal foils and laser cutting techniques [69]. Owing to the small Nemst diffusion layer thickness, fast mass transfer between the electrodes is achievable. The electrode surface area normalized by cell volume amounts to 40 000 m m". This value clearly exceeds the specific surface areas of conventional mono- and bipolar cells of 10-100 m m. ... 

Among MC lattice models of the double layer, it is also worth mentioning the work of Nazmutdinov et al. (1988), who used a lattice model involving two mono-layers of water molecules on the surface of an electrode, forming a hexagonal close-packed array. The interaction of each water molecule in contact with the metal surface (assumed to be Hg) was taken from quantum-mechanical calculations. Information was obtained concerning the relative numbers of molecules with different numbers of hydrogen bonds, and it was concluded that the hypothesis of an icelike state of water in a monolayer on Hg is rather unlikely. 

Electrochemical template-controlled sjmthesis of metallic nanoparticles consists of two steps (i) preparation of template and (ii) electrochemical reduction of metals. The template is prepared as a nano structured insulating mono-layer with homogeneously distributed planar molecules. This is a crucial step in the whole technology. The insulating monolayer has to possess perfect insulating properties while the template has to provide electron transfer between electrode and solution. Probably, the mixed nano-structured monolayer consisting of alkylthiol with cavities which are stabilized by the spreader-bar approach [19] is the only known system which meets these requirements. 

Mono- or single-crystal materials are undoubtedly the most straightforward to handle conceptually, however, and we start our consideration of electrochemistry by examining some simple substances to show how the surface structure follows immediately from the bulk structure we will need this information in chapter 2, since modern single-crystal studies have shed considerable light on the mechanism of many prototypical electrochemical reactions. The great majority of electrode materials are either elemental metals or metal alloys, most of which have a face-centred or body-centred cubic structure, or one based on a hexagonal close-packed array of atoms. 

A special case is when the electrochem-ically active components are attached to the metal or carbon (electrode) surface in the form of mono- or multilayers, for example, oxides, hydroxides, insoluble salts, metalloorganic compounds, transition-metal hexacyanides, clays, zeolites containing polyoxianions or cations, intercalative systems. The submonolayers of adatoms formed by underpotential deposition are neglected, since in this case, the peak potentials are determined by the substrate-adatom interactions (compound formation). From the ideal surface cyclic voltammetric responses, E° can also be calculated as... 

If the surface of a metal or carbon electrode is covered with a layer of some functional material, the electrode often shows characteristics that are completely different from those of the bare electrode. Electrodes of this sort are generally called modified electrodes [9] and various types have been developed. Some have a mono-molecular layer that is prepared by chemical bonding (chemical modification). Some have a polymer coat that is prepared either by dipping the bare electrode in a solution of the polymer, by evaporating the solvent (ethanol, acetone, etc.) of the polymer solution placed on the electrode surface, or by electrolytic polymerization of the monomer in solution. The polymers of the polymer-modified electrodes are either conducting polymers, redox polymers, or ion-exchange polymers, and can perform various functions. The applications of modified electrodes are really limit-... 

Finally, electrochemical pre-treatment is performed to obtain a reproducible surface. This is done mainly by cycling the applied potential over the entire potential window limited by the hydrogen and oxygen evolution reaction. Such a treatment has two functions first, removal of adsorbed species and, second, altering the microstructure of the electrode, the latter being caused by the repetitive dissolution and deposition of a metal mono-layer in the scanning procedure. 

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