Nernst potential-dependent

As noted in Equation 3.61, ksT je is 25.7 mV at 25°C. The value of the Nernst potential depends on the valency of the ion and the ratio of the ion concentrations in the outside and inside chambers. The Nernst equation in the form of Equation 8.15 is one of the fundamental formulas used in understanding ionic transport in neurons (Kandel et al. 1991,Weiss 1996, Hille 2001). 

Building on initial work [47], the main focus of SECM in the study of ET at ITIES has been to identify and understand the potential-dependence of ET rates. In these studies, the potential drop across an ITIES has been controlled by varying the concentration of potential-determining ions in the two phases. The potential drop across an ITIES follows the Nernst-Donnan equation [74,75],... 

Since the absolute and the conventional electrode potentials differ only by an additive constant, the absolute potential depends on the concentration of the reactants through the familiar Nernst s equation. This dependence is implicitly contained in Eq. (2.6) the real Gibbs energies of solvation contain an entropic term, which depends on the concentration of the species in the solution. 

The Nernst equation defining the potential of the silver-silver chloride electrode is Equation (14.9). Since the [CF] in such an electrode is a constant, the potential also must be a constant (the requirement of a reference electrode) because [CF] is the only variable on which the potential depends. 

Unlike anions that specifically adsorb at electrodes, cations normally do not lose their solvation shell due to their smaller size and are electrostatically adsorbed at electrodes at potentials negative to the pzc. However, depending on the affinity with the foreign substrate, cations can be reduced to a lower oxidation state or even discharged completely to the corresponding metal atom at the sub-monolayer or monolayer level at potentials positive to the equilibrium Nernst potential for bulk deposition. This deposition of metal atoms on foreign metal electrodes at potential positive to that predicted by the Nernst equation for bulk deposition has been called underpotential deposition and has been extensively investigated in recent years. Detailed discussion of the... 

RadSigma=5.6686e-6 %watt/m2-K4 Stefan-Boltzmann for radiation calculation %Define Thermodynamic Nernst Potential Temperature Dependent Parameters (this is for a specific fuel)... 

Open-circuit potential (OCP) — This is the - potential of the - working electrode relative to the - reference electrode when no potential or - current is being applied to the - cell [i]. In case of a reversible electrode system (- reversibility) the OCP is also referred to as the - equilibrium potential. Otherwise it is called the - rest potential, or the - corrosion potential, depending on the studied system. The OCP is measured using high-input - impedance voltmeters, or potentiometers, as in - potentiometry. OCP s of - electrodes of the first, the second, and the third kind, of - redox electrodes and of - ion-selective membrane electrodes are defined by the - Nernst equation. The - corrosion po-... 

If the semipermeable membrane is selective for a particular ion (i), a potential gradient will develop across the membrane. The gradient, described by the Nernst equation, depends on the ratio of the activity of the ion on either side of the membrane ... 

The exchange current density of adatoms is a thermodynamically well defined quantity. It depends on the Nernst potential or on the respective ion activity, and is, in general, as long as M ee N holds, independent of the surface topography. 

The deposition begins at potentials more positive than values where deposition of R occurs on bulk R. Consider, for example, the deposition of Ag on a 1-cm Pt electrode from a 0.01-L solution containing 10 M Ag". Let A = 1.6 X 10 cm and yo = yR. The potential for deposition of one-half of the silver (which forms about 0.05 monolayer) is = 0.35 V, compared to E = 0.43 V required for the same amount of deposition on a silver electrode. Deposition at potentials before that predicted by the Nernst equation with R = 1 is called underpotential deposition. The situation is much more complicated than the above treatment suggests, since the deposition potential depends on the nature of the substrate (material and pretreatment) and on adsorption of O. Also, the treatment assumes that formation of a second layer does not start until the first is complete. However, this is frequently not the case atoms of metal will often aggregate, rather than deposit on a foreign surface, and dendrites will form. Reviews on the nature of underpotential deposition and the deposition of solids in general are available (6-10). 

The acid-hase characteristics of the surface groups (relative speciation of surface groups as a function of pH in upper figure) determine the pH of zero potential (point of zero proton condition MeOHt = =MeO ). The Nernst equation—a surface potential dependence on pH of (RT/Fj In 10 (= 59 mvolt at 25°C)—is not fulfilled. The lines in the lower figure were calculated from alkalimetric and acidimetric titration curves using... 

A metal coating can inhibit or catalyze these reactions. Depending on the Nernst potential of the coating metal, the base metal will act as an anode or cathode. 

For the electrode plane ( = 0), two separate boundary conditions are required as the plane is composed of two different materials the electroactive microdisc and the insulating supporting surface. As the microdisc surface is electroactive, a potential-dependent boundary condition is applied the Nernst equation, Butler-Volmer or Marcus-Hush models may be used as appropriate. 

The term co(0, t) depends on the electrode potential (overpotential). For a reversible system (see below), the potential dependence of the concentrations can be described by the Nernst equation substituting the respective surface concentrations, but Eq. (1.3.39) and the following expressions are valid regardless of the actual kinetic properties of the system. 

The interface in question is not in thermodynamic equilibrium. For this to occur at least two different redox couples must be responsible for the value of the open-circuit potential. The overall zero current then corresponds to a chemical balance which is not null. This is the case for instance in corrosion. The open-circuit condition is not in equilibrium and the system changes with time. The open-circuit potential, which is not given by the Nernst law, depends on the properties of at least two redox couples in this instance one often refers to the term mixed potential. ... 

It can be seen that the corrosion current and potential depend on both the equilibrium potentials for the hydrogen evolution reaction and metal dissolution calculated from the Nernst equation, and the kinetic parameters, the exchange currents and the Tafel slopes. Table 9.1 shows the corrosion currents calculated for some typical values of these parameters it is also important to note that even a... 

This equation system is solved using damped Newton iterations. The Newton solver normally converges within 3 to 4 iterations. However, calculation of residual requires the evaluation of Nernst potential and the exchange current densities which are dependent on the partial pressures of Ha, HaO, and Oa at the three-phase boundary. 

The exchange current density depends on the component concentrations, as stipulated both by the mass action law and by the equilibrium (Nernst) potential [Eq. (58)] being a function of these concentrations. Substituting the latter relationship into Eq. (57), we obtain... 

Combining the Nernst equation for the preceding reaction with the dissociation of water shows that the reaction potential depends on pH as follows ... 

At this point, the Nernst potential is mainly a sodium potential, and it depends upon the distribution of the sodium ions on both sides of the membrane. 

Potential difference at the electrolyte layer Temperature-dependent Nernst potential difference of reactionj... 

Nernst points (5) out that, according to eq. (4a), liquid junction potentials depend only on the ratio of the two osmotic pressures pj and p and not on their absolute values. So if one makes a cell such that in one all the solutions are n times more concentrated than in the other, both must give the same liquid junction potential. Nernst called this the superposition principle and prefaced many of his discussions with it its validity (only approximate, in that osmotic coefficients are ignored) is ix)werful evidence for the complete dissociation of strong electrolytes. 

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