Cell voltage measurement

We would like to measure the contribution each half-reaction makes to the voltage of a cell. Yet every cell involves two half-reactions and every cell voltage measures a difference between their half-cell potentials. We can never isolate one half-reaction to measure its E°. An easy escape is to assign an arbitrary value to the potential of some selected half-reaction. Then we can combine all other half-reactions in turn with this reference half-reaction and find values for them relative to our reference. The handiest arbitrary value to assign is zero and chemists have decided to give it to the half-reaction... 

The cell voltage measurement in itself represents a point of decisive significance, where factors such as temperature of the measurement, and Nemstian behaviour and asymmetry of the electrode play a role together with the reliability and flexibility of the pH/mV meter. Such a meter consists of a null-point or a direct-reading meter. 

Fig. 3 Electrochemical cell for the definition of cell voltage measurement according to the IUPAC convention [51].

Such a cell voltage measured with respect to a reference electrode is called the electrode potential and is symbolized in the following text by the term Ue- Accordingly, the reference potential f/ ef (H2/H ) is actually set to zero. A scale and data for various systems are given in Appendix G. It should be mentioned here, that the symbol E rather than is generally used in the classical electrochemical literature. We prefer to use t/g for electrode potential because the symbol E is used for electron energies (see also ref. [7]). 

A cell voltage measured using an SCE reference electrode is —0.774 V. (The indicating electrode is the more negative half-cell.) What would the cell voltage be with a silver/silver chloride reference electrode (1 M KCI E = 0.228 V) or with anNHE ... 

E is the cell voltage measured and corresponds to flAg = 1. that is, equilibrium Ag/Ag2S [31]. The conclusion is that the strong change of the chemical potential of /iAg is caused by its electronic part ... 

We mentioned in Sect. 23.2 that galvanic cells can make the energy released by a chemical reaction usable, but they can also be utilized as a measuring instrument for the differences of redox potentials and therefore the electron potentials of various redox pairs. Moreover, because the electron potential itself is determined by the chemical potentials of the substances making up the redox pair, it is also possible to find the fi values as well as the drive A of the underlying total reaction with the help of galvanic cells. Reversible cell voltages measured with zero current can be used to determine these quantities and derived ones such as equilibrium constants. 

The cell voltage measured in (with or without the presence of I the stationary iodide concentration at the membrane/ solution interface. This concentration in turn is determined by the rate of dissolution of Agl and the rate of I transport from the electrode surface to the solution bulk. Thus, the cell voltage (which is not an... 

A. k-Factor. A popular diagnostic parameter that is measured and used in the chlor-alkali industry to monitor the performance of mercury and membrane electrolyzers and to control (manually or automatically) the anode-cathode in the mercury cells is the / -factor. The -factor is the slope of the current density-voltage curve, plotted from the cell voltages measured at dififerent loads. 

Cell voltage measurement at low current density 1. Fast 2. Locates damaged membranes 3. Detects large holes 1. Only possible during startup 2. Only possible with bipolar electrolyzers... 

Figure 4.5.72. Cell voltage (measured and calculated) and calculated voltage losses at the SOFC (Ni-cermet/YSZ/(La,Sr)Mn03) measured at 950°C at different current densities.

The most important factor, regardless of conditioning procedure, is that the cell voltage is considered stable before the actual measurement step starts. A stability criterion can be defined based on the deviation of the fuel-cell voltage measured... 

Before and after sample measurements, the potentiometric measuring cell is calibrated with standard solutions in the range of 3 x 10 -0.1 M. The slope of the response curve should be about 54 5 mV/decade at 25 °C. Between measurements, the sample half-cell must be carefully washed and dried to avoid cross contamination. The cell voltage measured in the sample solution must be in the voltage range obtained for calibrating standards. 

Such a cell voltage measured with respect to a reference electrode is called the electrode potential and is symbolized in the following text by the term U. Accordingly, the reference potential is actually set to zero. A scale and... 

Electromotive force (emf) The potential difference between the two electrodes in a cell. The cell emf is the cell voltage measured when no current is flowing through the cell. It can be measured by means of a pH meter with high input impedance. 

Fig. 10 Cell voltage measured during CO2 electrolysis (850 °C, —0.25 A cm , 70 % CO2-3O % CO) in the Ni/YSZ-based SOC when applying the inlet gases to the Ni/YSZ electrode as received and when applying cleaned gases [60]. Reproduced here with kind permission from The Electrochemical Society 2010...

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