Potential Nernst

In many epithelia Cl is transported transcellularly. Cl is taken up by secondary or tertiary active processes such as Na 2Cl K -cotransport, Na Cl -cotransport, HCOJ-Cl -exchange and other systems across one cell membrane and leaves the epithelial cell across the other membrane via Cl -channels. The driving force for Cl -exit is provided by the Cl -uptake mechanism. The Cl -activity, unlike that in excitable cells, is clearly above the Nernst potential [15,16], and the driving force for Cl -exit amounts to some 2(f-40mV. 

The equilibrium partition of ions present in the system gives rise to the equilibrium Galvani potential difference A (p = y (w) — (o) between the phases w and o (Nernst potential) [7,8]... 

The procedure described in the preceding section can form a basis for unambiguous determination of the Galvani potential difference between two immiscible electrolyte solutions (the Nernst potential) considering Eqs (3.1.22) and (1.4.34), e.g. for univalent ions,... 

The membrane potential expressed by Eqs (6.1.3) and (6.1.4) is termed the Nernst membrane potential as it originates from the analogous ideas as the Nernst equation of the electrode potential (p. 165) and the equation of the Nernst potential at ITIES (Eq. (3.3.50)). 

Fig. 6.24 A hypothetic scheme of the time behaviour of the spike linked to the opening and closing of sodium and potassium channels. After longer time intervals a temporary hyperpolarization of the membrane is induced by reversed transport of potassium ions inside the nerve cell. Nernst potentials for Na+ and K+ are also indicated in the figure. 

The concentration overpotential i/c is the component of the overpotential due to concentration gradients in the electrolyte solution near the electrode, not including the electric double layer. The concentration overpotential is usually identified with the Nernst potential of the working electrode with respect to the reference electrode that is, the thermodynamic electromotive force (emf) of a concentration cell formed between the working electrode (immersed in electrolyte depleted of reacting species) and the reference electrode (of the same kind but immersed in bulk electrolyte solution) ... 

The high stability of the metal clusters allows one to hold the sample potential slightly positive of the Nernst potential, typically at +10 mV versus Cu/Cu2 + in the case of copper. Thus, normal electrodeposition onto the sample directly from solution is prevented, whereas the tip-generated Cu clusters remain on the surface [96]. 

When a metal is in contact with its metal ion in solution, an equilibrium potential is established commonly referred to as Nernst potential (Er). Metal deposition occurs at potentials negative of Er, and dissolution for E > Er. However, when a metal is deposited onto a foreign metal substrate, which will always be the case for the initial stages of deposition, it is frequently observed that the first monolayer on the metal is deposited at potentials which are positive of the respective Nernst potential [37, 38]. This apparent violation for Nernst s law simply arises from the fact that the interaction between deposit metal and substrate is stronger than that between the atoms of the deposit. This effect has been termed underpotential deposition (upd), to contrast deposition processes at overpotentials. (One should keep in mind, however, that despite the symmetrical technical terms the physical origins of both effects are quite different. While the reason for an overpotential is solely due to kinetic hindrance of the deposition process, is that for underpotential deposition found in the energetics of the adatom-substrate interaction.)... 

The membrane potential reached in a system with only one permeant ion and no perturbing forces is called the equilibrium, or Nernst, potential for that ion thus, the final membrane potential for the system in Figure 6-2 is... 

The program reports in its output the resulting redox potential for each redox couple, as calculated from the Nernst equation. The Nernst potentials, arranged in decreasing order, are... 

Figure 9. Formation of Stern plane and diffuse layer on particle surface ( I 0 = surface or Nernst potential, = potential of inner Flelmholtz plane, I 5 = Stern potential, l = thickness of Stern plane, ZP = zeta potential at surface of shear, d = distance from particle surface).

To determine actual cell performance, three losses must be deducted from the Nernst potential activation polarization, ohmic polarization, and concentration polarization. Definition of the ohmic polarization is simply the product of cell current and cell resistance. Both activation polarization and concentration polarization required additional description for basic understanding. 

If reversibility is assumed at the outlet of each stack, no voltage losses are deducted from the Nernst potential. Therefore, each shaded area represents the maximum power, which each cell could generate. 

---