Open circuit electrode Nernst equation

It is important to note that equation (7.11), and thus (7.12) is valid as long as the effective double layer is present at the metal/gas interfaces. Therefore equation (7.11) is valid not only under open-circuit conditions (which is the case for the Nernst equation) but also under closed-circuit conditions, provided, of course, that the working electrode effective double layer is not destroyed. Consequently the importance of equation (7.11) is by no means trivial. 

The activation overpotentials for both electrodes are high therefore, the electrochemical kinetics of the both electrodes can be approximated by Tafel kinetics. The concentration dependence of exchange current density was given by Costamagna and Honegger.The open-circuit potential of a SOFC is calculated via the Nernst equation.The conductivity of the electrolyte, i.e., YSZ, is a strong function of temperature and increases with temperature. The temperature dependence of the electrolyte conductivity is expressed by the Arrhenius equation. 

Figure 3.37 illustrates the Nernst diffusion layer in terms of concentration-distance profiles for a solution containing species O. As pointed out previously, the concentration of redox species in equilibrium at the electrode-solution interface is determined by the Nernst equation. Figure 3.37A illustrates the concentration-distance profile for O under the condition that its surface concentration has not been perturbed. Either the cell is at open circuit, or a potential has been applied that is sufficiently positive of Eq R not to alter measurably the surface concentrations of the 0,R couple. 

The shape of the potential-time response is determined by the concentration changes of O and R at the electrode surface during electrolysis. The potential is related to Cq/Cr via the Nernst equation for a reversible system. The initial potential before current application is simply the rest potential or open-circuit potential (E ) of the solution, which reflects the initial Cq/C in solution. At the instant of current application, this ratio becomes finite and the potential changes to a value consistent with the Nernst equation. Early in the... 

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-... 

In general, the open-circuit potential measured between two reversible electrodes, which is also called electromotive force, /f 1, is defined by the Nernst equation. A simplified form of this equation for the electrochemical reaction (3) was given by Eq. (15). In general, the Nernst equation relates the activities (and/or fugacities) of the substances or species, a,-, in the cell s electrochemical reactions and the standard open-circuit potential, E°, of the cell as ... 

The equilibrium electrode potential is the electrical potential of an electrode measured against a reference electrode when there is no current flowing through the electrode. It is also called open circuit potential (OCP). The equilibrium potential between a metal and a solution of its ions is given by the Nernst equation as follows ... 

When the UME is moved close to an insulating surface, the current drops to a lower value Ij because the surface and the insulating sheath of the UME block transport of active species O. This effect is sometimes called negative feedback and is further enhanced by the fact that no reoxidation of R can occur at insulating parts of the surface. Approaching a conductive surface kept at an electrode potential where reoxidation of R is possible causes an opposite effect (positive feedback) and Ij is enhanced with a closer distance. Both possibilities are schematically depicted in Fig. 7.11. A similar effect may be observed with an unbiased (not kept at any specific potential, but instead at open circuit) surface. Because the large surface area is in contact with the solution containing a supply of O, the surface electrode potential is essentially controlled by the Nernst equation. At the potential established by the concentration of O, the reduced species R created at the UME will be reoxidized, whereas further O is reduced elsewhere on the surface. 

At zero current, the fuel cell electrodes provide the thermodynamic open circuit voltage Vceii = Voc- Connection of a load induces current I in the system and reduces Vceii by V I). The current drawn from the fuel cell thus costs some potential the thermodynamic voltage Vgc is the capital at our disposal. The value of Voc is given by Nernst equation [1] in this chapter, Voc is assumed to be constant, and we will focus on 6 V f). 

Open Circuit Potential. The potential difference measured between anode and cathode for an SOFC with an open electronic circuit. If the redox reactions occurring at the electrodes are known, the OCP can be predicted using the Nernst equation. 

Table 8.1 contains typical data obtained for one of IPS series. The open-circuit potential of Ag electrode in this IPS series is practically constant. Its average value (-0.376 V) coincides with the theoretical one following from the Nernst equation at the activity coefficient of Ag ions equal to 0.6. 

PCT diagrams of AB2 (electrode alloys)/H systems reflect multiphase or nonideal behavior. This is illustrated in Figure 9.21, which plots both the equilibrium pressure and the open-circuit equilibrium voltage, E, for Zr 5Ti.5V.5Ni11 Fe 2Mn 2-The pressure was calculated from using the Nernst equation [61]. The use... 

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