ON ,’" redox couple

In this review, after a brief overview of the structural and electronic properties of metal adlayers, there are six sections describing catalytic effects on redox couples, oxidation of organic molecules, carbon monoxide, organic electrosynthesis reactions, hydrogen evolution, oxygen reduction, and metal electrodeposition. Outside the scope of this review are other UPD processes that play a role in determining the catalytic properties of electrode surfaces such as the UPD of H and OH. 

In the three following sections, we focus on redox couples following the E mechanism (with Vox = VRed = 1). 

From an analytical viewpoint, the operativity of Eq. (20.7) means that high faradic currents can be achieved on redox couples with very reversible behavior. In cyclic voltammetry (CV) in fact, the reversibility of a redox system depends on the k° value and on the scan rate (v). Using conventional electrodes, reversible patterns are obtained when ... 

Calomel Electrodes Calomel reference electrodes are based on the redox couple between Hg2Cl2 and Hg (calomel is a common name for Hg2Cl2). 

Silvcr/Silvcr Chloride Electrodes Another common reference electrode is the silver/silver chloride electrode, which is based on the redox couple between AgCl and Ag. 

Metal-induced reductive dimerization of carbonyl compounds is a useful synthetic method for the formation of vicinally functionalized carbon-carbon bonds. For stoichiometric reductive dimerizations, low-valent metals such as aluminum amalgam, titanium, vanadium, zinc, and samarium have been employed. Alternatively, ternary systems consisting of catalytic amounts of a metal salt or metal complex, a chlorosilane, and a stoichiometric co-reductant provide a catalytic method for the formation of pinacols based on reversible redox couples.2 The homocoupling of aldehydes is effected by vanadium or titanium catalysts in the presence of Me3SiCl and Zn or A1 to give the 1,2-diol derivatives high selectivity for the /-isomer is observed in the case of secondary aliphatic or aromatic aldehydes. 

The sensitizers display a crucial role in harvesting of sunlight. To trap solar radiation efficiently in the visible and the near IR region of the solar spectrum requires engineering of sensitizers at a molecular level (see Section 9.16.3).26 The electrochemical and photophysical properties of the ground and the excited states of the sensitizer have a significant influence on the charge transfer (CT) dynamics at the semiconductor interface (see Section 9.16.4). The open-circuit potential of the cell depends on the redox couple, which shuttles between the sensitizer and the counter electrode (for details see Section 9.16.5). 

Although all potentiometric measurements (except those involving membrane electrodes) ultimately are based on a redox couple, the method can be applied to oxidation-reduction processes, acid-base processes, precipitation processes, and metal ion complexation processes. Measurements that involve a component of a redox couple require that either the oxidized or reduced conjugate of the species to be measured be maintained at a constant and known activity at the electrode. If the goal is to measure the activity of silver ion in a solution, then a silver wire coupled to the appropriate reference electrodes makes an ideal potentiometric system. Likewise, if the goal is to monitor iron(UI) concentrations with a platinum electrode, a known concentration of... 

Organic radical battery — Group of rechargeable - batteries based on a redox couple with one organic radical, e.g., the poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) radical. 

Redox potential and pH are closely related. The change in Eh per pH unit may range from 59 to 200 mV, depending on the redox couples and kinetics of reduction. Since Eh values represent mixed potentials, a simple correction of 59 mV per pH unit may not be adequate. 

Several groups have performed high-quality theoretical calculations on organic redox couples such as quinones and anilines. These calculations provide a calibration of the level of... 

Lithium insertion into titanium oxides plays on the redox couple Ti /TP at a potential of between 1.3 and 1.9 V versus Li/LL, depending on the polymorph. This potential window means that (1) safety risks linked to metallic lithium deposits can be avoided (intervening at 0 V) and (2) the copper collector can be replaced by less costly aluminum. 

The compounds Li3Cr2(P04)3 and Li3Fe2(P04)3 both show the same sequence of structural transitions as Li3Sc2(P04)3. These compounds form orthorhombic fast lithium ion conducting phases above 265 °C and 312 °C respectively and show conductivities ca 10 S cm at these temperatures. These compounds contain trivalent chromium and iron and so are susceptible to reduction. Whilst this is associated with an increase in the electronic conductivity that would render these materials unsuitable for use as an electrolyte in lithium batteries it does offer potential for use as an electrode material for lithium storage. The related compound Li3V2(P04)3 has been studied as a possible intercalation host for lithium cations based on the redox couple and transforma-... 

Organosulfides have been studied as cathode materials based on the redox couple of the S-S bonds in organodisulfides or thiolates [82, 83] ... 

Just as in the case of fluorination, the oxygenation of the surface, due to the presence of the strong dipoles mentioned already, leads to a variety of effects on different redox couples. ET... 

The active site on the surface of selective propylene ammoxidation catalyst contains three critical functionalities associated with the specific metal components of the catalyst (37—39) an a-H abstraction component such as Sb ", or Te" " an olefin chemisorption and oxygen or nitrogen insertion component such as Mo " or and a redox couple such as Fe " /Fe " or Ce " /Ce" " to enhance transfer of lattice oxygen between the bulk and surface... 

Potentiometric Titrations. If one wishes to analyze electroactive analytes that are not ions or for which ion-selective electrodes are not available, two problems arise. First, the working electrodes, such as silver, platinum, mercury, etc, are not selective. Second, metallic electrodes may exhibit mixed potentials, which may arise from a variety of causes. For example, silver may exchange electrons with redox couples in solution, sense Ag" via electron exchange with the external circuit, or tarnish to produce pH-sensitive oxide sites or Ag2S sites that are sensitive to sulfide and haUde. On the other... 

A closer analysis of die equilibrium products of the 1 1 mixture of methane and steam shows the presence of hydrocarbons as minor constituents. Experimental results for die coupling reaction show that the yield of hydrocarbons is dependent on the redox properties of the oxide catalyst, and the oxygen potential of the gas phase, as well as die temperamre and total pressure. In any substantial oxygen mole fraction in the gas, the predominant reaction is the formation of CO and the coupling reaction is a minor one. 

This method involves very simple and inexpensive equipment that could be set up m any laboratory [9, 10] The equipment consists of a 250-mL beaker (used as an external half-cell), two platinum foil electrodes, a glass tube with asbestos fiber sealed m the bottom (used as an internal half-cell), a microburet, a stirrer, and a portable potentiometer The asbestos fiber may be substituted with a membrane This method has been used to determine the fluoride ion concentration in many binary and complex fluondes and has been applied to unbuffered solutions from Willard-Winter distillation, to lon-exchange eluant, and to pyrohydrolysis distil lates obtained from oxygen-flask or tube combustions The solution concentrations range from 0 1 to 5 X 10 M This method is based on complexing by fluonde ions of one of the oxidation states of the redox couple, and the potential difference measured is that between the two half-cells Initially, each cell contains the same ratio of cerium(IV) and cerium(tll) ions... 

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