Voltage Characteristic

Similar current-voltage curves were reported [27] for the hydrogen-oxygen fuel cell with different solid solutions of Ce03—La2 03 as electrolyte. However, the solid electrolytes possessed some electronic conductance. Although the addition of Th02 reduced the electronic conductance, it led to an undesirable decrease in performance. 

Current-voltage curves (a, b) for the oxidation of converted propane are shown in Fig. 89 together with a curve (c) for the oxidation of hydrogen. The curves were taken [5] at 1000°C in a cell with Zro.gs Cao.15 Oi.ss as solid electrolyte and porous platinum electrodes. The oxygen pressure was 1 atm. The curves for the oxidation of converted propane are linear and parallel to the curve for the oxidation of hydrogen in a wide potential 

Processes in Fuel Cells with Solid Electrolytes 

The properties of the interface at which the formation of oxide ions occurs have been of special interest [6, 7, 28—35]. While solid electrocatalysts, Pt [28, 29, 31, 32] and C [30], were studied mainly, a molten silver cathode was employed in another type of zirconia-electrolyte fuel cell developed [34,35] at the General Electric Research and Development Center in Schenectady. Since the hindrance of the electrochemical steps of the O2 reduction at the cathode surface is small [28, 32] on platinum around 1000 °C, it is hard to elucidate the reaction mechanism beyond the net reaction 1. Analysis [33] of the potential distribution curves inside Zro 9Yo 2 02.i in contact with two platinum electrodes showed at 1380°C that the electronic hole contribution to the conductivity in the bulk of the specimen depended upon as would be expected from the equilibrium of reaction 15. The partial oxygen pressure had values between 10 and 10 atm. However, if the production of oxide ions is assumed to occur at the cathode solely by reaction 15, the rate of production is much lower than the rate of loss at the anode. A cathodic reaction of the type 

Binder, H., A. Kohling, H. Krupp, K. Richter, and G. Sandstede Electrochim. 

If local traps are distributed in energy (E), they will be filled from bottom to top as electric fields, F, increase. The quasi-Fermi level will scan the distribution shifting towards the transport band, and 0 = rif/rit will become a function of F. A general form of nt = nt(iif) relation can be obtained from a detailed balance equation as [363] 

In studies of low-mobility insulators, two types of continuous trap distributions are commonly used the exponential distribution of traps [364] and the Gaussian distribution of traps [365]. 

The problem has been solved analytically for an exponential distribution of traps 

This general solution is usually approximated by Mark and Helfrich [366] 

The conductivity and j-U characteristic given by Eq. (187) is similar to the result following the Poole-Frenkel effect on SCL currents [376,377]. Such a situation is clearly not expected in the case of the standard solution for trapping by a discrete set of separated microtraps expressed by Eqs. (167) and (168). This is the case if one extrapolates Eq. (185) to l 0, with = (Neff/N0) exp(—Et/kT). The physical meaning of this extrapolation is that we deal with one discrete trap level (Et), the trap potential being the infinitely sharp point well for which the barrier lowering can be neglected. 

To describe the current it is helpful to define the collection efficiency N where N compares the flux of electrons out to the flux of photons in 

Detailed analysis shows that the maximum power, developed by the cell is given by - 

In eqn (14) the load on the cell has been optimised to achieve the maximum power. The collection efficiency is close to unity and there is a fill factor of about 0 8. The 0-04 V term which reduces the cell voltage from AE arises from the fact that the concentration of B is less than that of A at the illuminated electrode and so there is a Nernst term. If one expresses this power output as a power conversion efficiency then the theoretical ideal cell could achieve efficiencies as high as 20%. However this requires that all the different conditions in the recipe for success should be met. Can this be achieved  

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Eig. 6. Comparison of current density and cell voltage characteristics of the electrolysis systems where lines A and B represent steam electrolysis and the use of SPE, respectively, the conventional KOH water electrolysis, and, 2ero-gap cell geometry employing 40% KOH, at 120—140°C. 

Fig. 5. NMOS capacitance voltage characteristics where C is the oxide capacitance, A shows low frequency characteristics, and B shows high frequency characteristics. At low frequencies C approaches C for negative voltages (accumulation) and positive voltages (inversion). In the flat-band (FB) condition there is no voltage difference between the semiconductor s surface and bulk. The threshold voltage, Dp for channel formation is the point where the...

Fig. 5. Dark(current—voltage) characteristics ofp—n ( ) andp—i—n (A) junctions at 295 K.

Fig. 10. Power and voltage characteristics of the nickel—iron cell where the internal resistance of the cell, R, is 0.70 mQ, at various states of discharge ( )...

Arresters or diverters are generally of the following types and the choice between them will depend upon the power frequency system voltage, characteristics of the voltage surges and the grounding system, i.e. 

ZnO blocks have extremely non-linear, current-voltage characteristics, typically represented by... 

Figure 3-29 Forward conduction voltage characteristic of the Schottky versus the ultrafast diode.

Fig. 2. Current-voltage characteristics taken at points (1), (2), and (3) in Fig. 3. The top insert shows the conductance versus voltage plot, for the data taken at point (3) (adapted from Oik el al. I]).

This figure demonstrates that also under potentiometric conditions (- no external current flow) electrochemical net reactions occur. The EMF of the zinc-amalgam in a given Zn2 -ion solution depends on the current-voltage characteristic of other ions (in this example, Cu2 and Pb2 are interfering ions with respect to the Zn2 equilibrium potential) at the amalgam electrode. EMF drifts are thus explainable. 

The current-voltage and luminance-voltage characteristics of a state of the art polymer LED [3] are shown in Figure 11-2. The luminance of this device is roughly 650 cd/m2 at 4 V and the luminous efficiency can reach 2 lm/W. This luminance is more than adequate for display purposes. For comparison, the luminance of the white display on a color cathode ray tube is about 500 cd/m2l5J. The luminous efficiency, 2 lm/W, is comparable to other emissive electronic display technologies [5], The device structure of this state of the art LED is similar to the first device although a modified polymer and different metallic contacts are used to improve the efficiency and stability of the diode. Reference [2] provides a review of the history of the development of polymer LEDs. 

Figure 11-2. Current-voltage and luminance-voltage characteristics of a stale of the art polymer LED.

Figure 13-3. Typical currcm-voliagc and radiance-voltage characteristics of an MEH-PPV-based 01.MJ with an Au anode and an IIO cathode.

There have been numerous studies of the electrical and emission properties of conjugated polymer-, small molecule-, and molecularly doped polymer-based OLEDs. The current-voltage and radiance-voltage characteristics have been nica sured as a function of thickness of the organic layer, temperature, different metal electrodes, etc. in an attempt to understand the device physics. A major factor in hibiting progress is the purity of the organic impurities that are incorporated dur-... 

Figure 15-19. Dark currenl versus voltage characteristics of the 1TO/MEH-PPV/ C(l /Au device at room temperature (reproduced by permission of the American Institute of Physics from Ref. [89]).

Recently, Mailiaras et al. [ 1511 have shown that for the analysis of the current-voltage characteristics of single layer OLEDs, it is of fundamental importance to properly account for the built-in potential. The electrical characteristics of MEH-... 

To calculate the current-voltage characteristic of a MESFET, we assume that the conducting channel is at thermal equilibrium, and the space-chaige layer completely depleted. Eq. (14.28) becomes... 

However, although it allowed a correct description of the current-voltage characteristics, this model presents several inconsistencies. The main one concerns the mechanism of trap-free transport. As noted by Wu and Conwell [1191, the MTR model assumes a transport in delocalized levels, which is at variance with the low trap-free mobility found in 6T and DH6T (0.04 cm2 V-1 s l). Next, the estimated concentrations of traps are rather high as compared to the total density of molecules in the materials (see Table 14-4). Finally, recent measurements on single ciystals [15, 80, 81] show that the trap-free mobility of 6T could be at least ten times higher than that given in Table 14-4. 

The first realization of a conjugated polymer/fullerene diode [89] was achieved only recently after the detection of the ultrafasl phoioinduced electron transfer for an lTO/MEH-PPV/CW)/Au system. The device is shown in Figure 15-18. Figure 15-19 shows the current-voltage characteristics of such a bilayer in the dark at room temperature. The devices discussed in the following section typically had a thickness of 100 nm for the MEH-PPV as well as the fullerene layer. Positive bias is defined as positive voltage applied to the 1TO contact. The exponential current tum-on at 0.5 V in forward bias is clearly observable. The rectification ratio at 2 V is approximately l()4. 

The power density / (Wkg-1) of the element results if the power is related to the battery weight. Figure 7 shows the current-voltage characteristic of a Leclanche element. 

Figure 7. Current-voltage characteristic of a Le-clanche element.

An important experimentally available feature is the current-voltage characteristic, from which the terminal voltage ([/v ) supplied by the electrochemical cell at the corresponding discharge current may be determined. The product of current / and the accompanying terminal voltage is the electric power P delivered by the battery system at a given time. 

FIG. 10 Current-voltage characteristics of polyanihiies LS films of 40 monolayers deposited on interdigitated electrodes (1) PANI, (2) POT, (3) POAS, (4) PEOA. 

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