Cell voltage cathode potential

Also called cell voltage, the potential difference between two half-cells, one at which oxidation occurs (anode) and one with reduction (cathode)... 

As the cell is discharged, Zn2+ ions are produced at the anode while Cu2+ ions are used up at the cathode. To maintain electrical neutrality, SO4- ions must migrate through the porous membrane,dd which serves to keep the two solutions from mixing. The result of this migration is a potential difference across the membrane. This junction potential works in opposition to the cell voltage E and affects the value obtained. Junction potentials are usually small, and in some cases, corrections can be made to E if the transference numbers of the ions are known as a function of concentration.ee It is difficult to accurately make these corrections, and, if possible, cells with transference should be avoided when using cell measurements to obtain thermodynamic data. 

Figure 1.5 The slope of E ath versus log /orr through the fuel-cell-relevant potential range has an apparently constant value near RT/F (measured current density, here designated i, is corrected for hydrogen crossover current, designated i and the measured cell voltage is ir-corrected to provide the cathode potential E) [Neyerlin et al., 2006].

The third limitation is concerned with the numerous contributions to the cell voltage Vceii, which, along with the difference in the electrode reversible potentials AEeq, comprises overpotentials at the cathode, tjc, and the anode, as well as the ohmic drop A ohmic ... 

In redox mediation, to have an effective electron exchange, the thermodynamic redox potentials of the enzyme and the mediator have to be accurately matched. For biocatalytic electrodes, efficient mediators must have redox potentials downhill from the redox potential of the enzyme a 50 mV difference is proposed to be optimal [1, 18]. The tuning of these potentials is a compromise between the need to have a high cell voltage and a high catalytic current. Furthermore, an obvious requirement is that the mediator must be stable in the reduced and oxidized states. Finally, for operation of a membraneless miniaturized biocatalytic fuel cell, the mediators for both the anode and the cathode must be immobilized to prevent power dissipation by solution redox reactions between them. 

For HCI electrolysis the cathodic reaction product is water, which is easily drained through the ODC without affecting the membrane water content. Consequently, the ODC can be attached directly to the membrane and pressure compensation is not necessary. The cell concept, which was developed in another co-operation with DeNora, could not be simpler - the basic cell principle is shown in Fig. 4.6. Initial laboratory tests conducted in 1994 at Bayer on the basis of old GE developments [4] demonstrated the feasibility of HCI electrolysis with ODC and the potential for a reduction of the cell voltage to about one-third of present values. 

The difference between the potential energy at the anode and the potential energy at the cathode is the electric potential, E, of a cell. The unit used to measure electric potential is called the volt, with symbol V. Because of the name of this unit, electric potential is more commonly known as cell voltage. Another name for it is cell potential. A cell potential can be measured using an electrical device called a voltmeter. 

La photovoltaic cells, the same redox reaction, OX + e = KED, may be used for both the anode and the cathode. Figure 10-33 shows an eneigy diagram of an operating photovoltaic cell this cell consists of a metallic cathode and a photoexcited n-type semiconductor anode. The electromotive force (the open cell voltage), ph > approximately equals the difference between the flat band potential of... 

From the energy diagram shown in Fig. 10-33, the operating cell voltage, V,, is obtained, as expressed in Eqn. 10-60, by subtracting from the electromotive force AEph the potential barrier of the space charge layer, the cathodic overvoltage t h, and the iR drop in the electrolyte ... 

The net result of current flow in a fuel cell is to increase the anode potential and to decrease the cathode potential, thereby reducing the cell voltage. Figure 2-3 illustrates the contribution to polarization of the two half cells for a PAFC. The reference point (zero polarization) is hydrogen. These shapes of the polarization curves are typical of other types of fuel cells. 

Summing of Cell Voltage The cell voltage includes the contribution of the anode and cathode potentials and ohmic polarization ... 

The cell voltage, E(J), defined as the difference between the cathode potential 2 and the anode potential 1, can thus be expressed as... 

In addition, in a DAFC, the proton exchange membrane is not completely alcohol tight, so that some alcohol leakage to the cathodic compartment will lead to a mixed potential with the oxygen electrode. This mixed potential will decrease further the cell voltage by about 0.1-0.2 V. It turns out that new electrocatalysts insensitive to the presence of alcohols are needed for the DAFC. 

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