Measured open-circuit voltages

Table 5.2 compares the measured open-circuit voltages with the difference in the work functions (A(p) of the electrodes. The table shows that with the exception of calcium, the open-circuit voltage increases linearly with the work function difference. However there is an additional constant 1 V contribution to the open-circuit voltage that cannot be accounted for by the difference in work functions. Calcium work function is smaller... 

Uniqueness of the Pt Catalyst The high overpotential at the PEFC cathode is the single most important source of loss in the PEFC, as it is in other low-temperature fuel cells. The sluggish nature of the ORR process is immediately reflected by the measured open-circuit voltage of around 1.0 V, to be compared with the thermodynamically expected value of... 

Fig. 14 Experimentally, a linear relationship between the HOMO level of the conjugated polymer (corresponds to onset of oxidation with respect to the Ag/AgCl reference electrode) and the measured open circuit voltage ( oc) has been determined for a large number of donor polymers. (Reproduced from [102] with permission, 2006, Wiley-VCH)...

One of the important advantages of primary batteries eonsists of very simple maintenance procedures. Most such batteries require no servicing. Before a battery is switched on, its appearance and the remaining service life are checked sometimes actual parameters are measured (open-circuit voltage (OCV) and the initial discharge voltage). Correct polarity and reliable contacts must be ensured a violation of polarity correspondence may result in serious disorders and even in the breakdown of load circuitry, especially circuits involving transistors and electrolytic capacitors. 

Figure 19. Comparison of best measured open circuit voltages for MIS and p-n junction devices. Note the departure from simple theory in both cases.

Table 3. Measured open circuit voltages (volts) and short circuit... 

A higher current density of 0.52 amp cm was obtained for the SPTES-50 polymer membrane-based MEA as compared with a current density of 0.24 amps cm for Nafion-117 membrane-based MEA at 0.6 V potential. Similarly, a higher peak power density of 0.34 W cm was obtained using SPTES-50 polymer membrane compared with 0.16 W cm using Nation-117 membrane in MEAs, measured under the same conditions. Estimates of hydrogen fuel permeability based upon measured open circuit voltage (OCV) indicate that SPTES-50 MEA and Nafion-117 exhibit similar rates of fuel crossover. 

For the measurement of gas components like hydrocarbons (HC) or nitric oxides (NOx) in non-equilibrated gas phases kinetically determined sensors are used (Fig. 19.2 middle).Depending on the electrode material, the gas components do not equilibrate on the measuring electrode at temperatures <700 °C. Thus gas components which are not thermodynamically stable are electrochemically active. In an HC- and 02-containing gas, for example, at least two electrode reactions can take place the electrochemical reduction of oxygen and the electrochemical oxidation of hydrocarbons. The measured open-circuit voltage does not obey the Nemst equation. Therefore such electrode behaviour is often referred to non-Nernstian electrodes (or mixed potential sensors). The cell voltage depends logarithmically on the concentrations of the hydrocarbons ... 

The temperature dependence of the open circuit voltage has been accurately determined (22) from heat capacity measurements (23). The temperature coefficients are given in Table 2. The accuracy of these temperature coefficients does not depend on the accuracy of the open circuit voltages at 25°C shown in Table 1. Using the data in Tables 1 and 2, the open circuit voltage can be calculated from 0 to 60°C at concentrations of sulfuric acid from 0.1 to 13.877 m. 

Secondary Voltage of Wound-Rotor Motors. The secondary voltage of wound-rotor motors is the open-circuit voltage at standstill, measured across the slip rings, with rated voltage applied on the primary winding. 

Friend et at. studied the influence of electrodes with different work-functions on the performance of PPV photodiodes 143). For ITO/PPV/Mg devices the fully saturated open circuit voltage was 1.2 V and 1.7 V for an ITO/PPV/Ca device. These values for the V c are almost equal to the difference in the work-function of Mg and Ca with respect to 1TO. The open circuit voltage of the ITO/PPV/A1 device observed at 1.2 V, however, is considerably higher than the difference of the work-function between ITO and Al. The Cambridge group references its PPV with a very low dark carrier concentration and consequently the formation of Schottky barriers at the PPV/Al interface is not expected. The mobility of the holes was measured at KT4 cm2 V-1 s l [62] and that for the electrons is expected to be clearly lower. 

Equilibrium potentials can be calculated thermodynamically (for more details, see Chapter 3) when the corresponding electrode reaction is known precisely, even when they cannot be reached experimentally (i.e., when the electrode potential is nonequilibrium despite the fact that the current is practically zero). The open-circuit voltage of any galvanic cell where at least one of the two electrodes has an nonequilibrium open-circuit potential will also be nonequilibrium. Particularly in thermodynamic calculations, the term EMF is often used for measured or calculated equilibrium OCV values. 

The fill factor is obtained by dividing the product of current and voltage measured at the power point by the product of short-circuit current and the open-circuit voltage. The power point is the maximum product of the cell voltage and the photocurrent obtained on the I V plot (see Section 9.16.4.5). The open-circuit voltage is the potential of the illuminated electrode, where the short-circuit current (7SC) is zero. 

We used the temperature dependence of the open circuit voltage (OCV) at constant composition x in LixC6 to measure the entropy variation AS(x) expressed by ... 

Suspended Probe Measurements Revisited. One group has explored the use of suspended probes to gain more useful qualitative electrostatic data in fluidized beds by developing a capacitive circuit model forthe bed (Rojo etal., 1986). Open-circuit voltages induced on immersed... 

PV current-voltage and power-voltage characteristics of a standard GaInP2/GaAs tandem cell were measured under 100 mW/cm2 illumination. The PV parameters under illumination were an open-circuit voltage Vroc = 2.32 V, a short-circuit current density Jsc = 13.4 mA/cm2, a fill factor FF = 0.88, and a PV conversion efficiency of 28.5%. Under the... 

The PV characteristics of the CIGS2 thin-film solar cell on opaque Mo back contact, as measured at the NREL under AM 1.5 conditions, were as follows short-circuit current density sc of 20.88 mA/cm2, open-circuit voltage 1% of 830.5 mV, fill factor FF of 69.13%, and PV conversion efficiency // of 11.99%. 

The photocurrent density of nanotube array samples fabricated in an electrolyte of 1.2 g of NH4F in a solution of 5 ml deionized water + 95 ml formamide at 35 V is shown in Fig. 5.46(a). The resulting nanotube array samples were 30 pm in length, with an outer diameter of 205 nm. The samples were annealed at 525°C and 580°C for 1 hour in oxygen prior to measurement. The 580°C annealed sample had an open circuit voltage Voc of -0.925 V (vs. Ag/AgCl) the 525°C annealed sample had an open circuit voltage... 

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