Potential, chemical electrode

Figure 7.14. Schematic representation of the spatial variation of electrode potential, chemical potential of oxygen and electrochemical potential of O2 for the cell 02, M1YSZ1M, 02 (=1 atm).

Ant Antelman, M.S., Harris jr., F.J. The Encyclopedia of Chemical Electrode Potentials, New York Plenum Press, 1982. 

Antelman, M. S., and F. J. Harris, Jr., The Encyclopedia of Chemical Electrode Potentials, Plenum Press, New York, 1982. 

The wide applicability of the electrochemical processes in the chemical processing industry (CPI) derives from the fact that the electron is a versatile reagent. Thus the electron can - unlike standard chemical reagents - be readily removed (oxidation) or added (reduction). Depending on its potential, the electrode can either oxidize or reduce various chemical species to convert them into profitably salable products without the undesirable byproducts. 

In contrast to acidic electrolytes, chemical dissolution of a silicon electrode proceeds already at OCP in alkaline electrolytes. For cathodic potentials chemical dissolution competes with cathodic reactions, this commonly leads to a reduced dissolution rate and the formation of a slush layer under certain conditions [Pa2]. For potentials slightly anodic of OCP, electrochemical dissolution accompanies the chemical one and the dissolution rate is thereby enhanced [Pa6]. For anodic potentials above the passivation potential (PP), the formation of an anodic oxide, as in the case of acidic electrolytes, is observed. Such oxides show a much lower dissolution rate in alkaline solutions than the silicon substrate. As a result the electrode surface becomes passivated and the current density decreases to small values that correspond to the oxide etch rate. That the current density peaks at PP in Fig. 3.4 are in fact connected with the growth of a passivating oxide is proved using in situ ellipsometry [Pa2]. Passivation is independent of the type of cation. Organic compounds like hydrazin [Sul], for example, show a behavior similar to inorganic ones, like KOH [Pa8]. Because of the presence of a passivating oxide the current peak at PP is not observed for a reverse potential scan. 

An alternative, but equivalent, approach to the problem of the effect of changes of potential on electrode kinetics is the formal separation of the free energy of activation into chemical and electrochemical components [32a, b]. This treatment will be followed in Sect. 4.2 for the analysis of multiple charge transfer at electrodes. 

Developers of thick-film sensors have removed the interference from the sample by chemical oxidation [12,13], by-passed it by selection of applied potentials and electrode materials, including the use of redox mediators [14,15], and kept it from electrode surfaces by inner and outer membranes [16-19]. 

The equilibrium situation in an electrochemical cell is obtained, if the electrical current is interrupted, if all local actions (e.g. transport in the electrode) have come to an end and no internal short circuits occur. Then, as mentioned (Figure 3.5.10), the cell voltage is determined by the difference in the lithium potential (chemical potential of lithium) between the left-hand side (Ihs) and right-hand side (rhs) of the electrochemical cell (E - open cell voltage, F - Faraday constant) ... 

Refs. [i] Latimer WM (1952) Oxidation potentials. Prentice-Hall, Englewood Cliffs [ii] Parsons R (1985) Redox potentials in aqueous solutions a selective and critical source book. Marcel Dekker, New York [Hi] Bard AJ, Parsons R, Jordan J (1985) Standard potentials in aqueous solutions. Marcel Dekker, New York [iv] Antelman MS, Harris FJ (eds) (1982) The encyclopedia of chemical electrode potentials. Plenum Press, New York [v] Pourhaix M (1963) Atlas d equilibres electrochemiques. Gauthier-Villars, Paris [vi] Bratsch SG (1989) J Phys Chem Ref Data 18 1 [vii] InzeltG (2006) Standard potentials. In Bard AJ, Stratmann M, Scholz F, Pickett CJ (eds) Inorganic electrochemistry. Encyclopedia of electrochemistry, vol. 7a. Wiley-VCH, Weinheim, chap 1 [viii] Stanbury DM (1989) In Sykes AG (ed) Advances in inorganic chemistry, vol. 33. Academic Press, New York, p 69 [ix] Wayner D, Parker VD (1993) Acc Chem Res 26 287... 

The DPET is designed to hold 1720 L (10.8 bbl) and operates safely at pressures up to 517 kPa (75 psi) and temperatures up to 150 C (300 T). The application of a high-voltage, dual-polarity electric potential to electrodes inside the vessel is used to coalesce and remove small droplets of water in the oil emulsion. The oil should be degassed and have a water content less than 15% before entering the vessel however, the treater does have the capability for free-water knockout. Preheated emulsion is pumped into the bottom portion of the vessel, below the electrodes, where free water generated by heating or chemical treatment may drop out. As more emulsion is... 

Comprehensive sources for standard electrode potentials include Standard Potentials in Aqueous Solution, A. J. Bard, R. Parsons, and J. Jordan, Eds. New York Marcel Dekker, 1985 G. Milazzo and S. Caroli, Tables of Standard Electrode Potentials. New York Wiley-Interscience, 1977 M. S. Antelman with F. J. Harris. Jr., The Encyclopedia of Chemical Electrode Potentials. New York Plenum Press, 1982. Some compilations are arranged alphabetically by element others are tabulated according to the numerical value oiEf. 

Equivalence-point potential The electrode potential of the system in an oxidation/reduction titration when the amount of titrant that has been added is chemically equivalent to the amount of analyte in the sample. 

Formality, F The number of formula masses of solute contained in each liter of solution synonymous with analytical molarity. Formal potential, The electrode potential for a couple when the analytical concentrations of all participants are unity and the concentrations of other species in the solution are defined. Formula weight The summation of atomic masses in the chemical formula of a substance synonymous with gram formula weight and molar ma.ss. 

On the other hand, well engineered manufacturing operations depend on the availability of manipulated variables for real-time feedback control. These variables usually operate at macroscopic length scales (e.g. the power to heat lamps above a wafer, the fractional opening of valves on flows into and out of a chemical reactor, the applied potential across electrodes in an electrochemical process). The combination of a need for product quality at the molecular scale with the economic necessity that feedback control systems utilize macroscopic manipulated variables motivates the creation of methods for the simulation, design and control of multiscale systems. 

Finally, a brief overview was presented of important experimental approaches, including GITT, EMF-temperature measurement, EIS and PCT, for investigating lithium intercalation/deintercalation. In this way, it is possible to determine - on an experimental basis - thermodynamic properties such as electrode potential, chemical potential, enthalpy and entropy, as well as kinetic parameters such as the diffusion coefficients of lithium ion in the solid electrode. The PCT technique, when aided by computational methods, represents the most powerful tool for determining the kinetics of lithium intercalation/deintercalation when lithium transport cannot be simply explained based on a conventional, diffusion-controlled model. 

By measuring the cell potential at various concentrations of Cu ", we can determine < cu2+/cu = 0cu2+/cu- This standard potential is tabulated along with the standard potentials of other half-cells in Table 17.1. Such a table of half-cell potentials, or electrode potentials, is equivalent to a table of standard Gibbs energies f rom which we can calculate values of equilibrium constants for chemical reactions in solution. Note that the standard potential is the potential of the electrode when all of the reactive species are present with unit activity, a = 1. 

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