I-V curves

Overall reaction H2 (positive electrode) H2 (negative electrode) (R. 4.10) 

After a fuel cell is conditioned, it will be evaluated under various conditions, such as different temperatures, reactant stoichiometric ratios, reactant 

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In Fig. 4.3.3b we present a V — I curve with a turning point and a negative differential resistance region with current saturation, computed for the same values of parameters Ni, A, cq as in Fig. 4.3.3a. This V—I curve corresponds to the upper and the middle solution branches. The range of parameters in which the high current solutions exist is again evaluated below, via an asymptotic treatment for /— oo. 

As seen in Figure 6.8, the fuel cell with 0.8 mg/cm2 Nafion content in the catalyst layer exhibited the best performance. To the researchers surprise, the performance of the fuel cell with 2.0 mg/cm2 Nafion content dropped sharply when the current was over 300 mA/cm2. The linear zone of the V-I curve with 2.0 mg/cm2 Nafion content is much shorter than that for the other two cases. This certainly would contribute to mass transport limitations within the catalyst layer under high ionomer loading. 

A competitive cell is likely to have in its V/I curve (Figure 6.5) a small IR drop (thin electrolyte film) and an extended current range before concentration polarisation sets in. In the SOFC, moreover, an expensive platinum catalyst is avoided due to high reaction rates at high temperature. Engineering for mass production is very important to the achievement of low capital cost, for example the Rolls-Royce fuel cell (Section 4.3). Its compact stack arrangement is described in US patent 2003/0,096,147 Al, an improved version of the previous patents. 

Figure 14.19 V-I curves for the argon magnetron glow discharge plasma at a pressure of 30 mtorr.

FIGURE 27.49 V-I curve of Aciplex membranes. Cell performance was evaluated with a single cell of 10 cm electrode area. The Pt loadings of anode and cathode were about 0.1 and 0.2 mg cm , respectively. Source Asahi Kasei. (From Wakizoe, M., Kodani, T., and Ota, T., Abstracts of the 2003 Fuel Cell Seminar, 2003.)... 

FIGURE 27.57 V-I curve of a cross-linked FEP 25 membrane for a 0.5 M aqueous methanol solution at a cell temperature of 110°C. The anodic flow rate was about 37 mL min and the air stoichiometry was 2. (Reproduced from Geiger, A.B., Rager, T., Matejek, L., Scherer, G.G., and Wokaun, A., in Proceedings of the 1st European PEFC Forum, Btichi, F.N., Scherer, G.G., and Wokaun A. (Eds.) 2001. With permission.)... 

FIGURE 27.62 (A) V-I curve and (B) ohmic resistance of a PEMEC using F t-Ti02-PEM operated at 80°C and ambient pressure with no... 

The V-I curve of the multilayer composite, which had the same structure as in the... 

But hold on a minute longer. Look at the published V-I curve (the black part of Figure A-3). This represents a typical integrated switcher device, rated for 1.5A. The device is therefore supposed to function up to 100°C at 1.5 A. But does the curve extend all the way Not at all The 100°C is mysteriously truncated No other information is available in the datasheet. The only way out for us as designers is to try to extrapolate the V-I curve. See gray part. 

Electrolyzer 1 still has the starting or ideal characteristics and electrolyzer 2 has suffered the damage. We also assume that the damage shows as an increase in the slope of the V-I curve. In other words, a = a = 02 and k2 > k. Now... 

The current through each electrolyzer is inversely proportional to the slope of its V-I curve. This slope is the / -factor familiar in the chlor-alkali industry. In the authors experience, differences of 10% in current density between electrolyzers are common in bipolar cell rooms operating in this mode. We shall return to the effects of differing current densities below. First we compare the power consumption of the above system with one that holds the two electrolyzer amperages equal. 

The polarization analysis consisted in the fitting of the experimental V-I curves with a proposed polarization model. The model has been already presented in equation (5). 

Srinivasan and Gileadi have analyzed the potential sweep method from the theoretical viewpoint and derived equations relating the shift in the adsorption peaks and the changes in the form of the V-i curves with sweep rate to the specific rate constants of the reaction involved. 

When Figure 4.4 is rotated coimter clockwise for 90° it becomes the familiar V-I curve as shown in Figure 2.2. It is not surprising because they basically represent the same thing but carried out under different conditions. 

MTI DMFCs also showed good durability in stacks. Figure 7.9 shows the average unit cell output power change in about 2700 hours. In the first 1800 hours, the average cell voltage was set at 0.45 V, and afterward it was set at 0.425 V to accommodate the downward shift of the V-I curves. The average cell decay rate was 4.3% per 1000 hours. 

Many statements and descriptions are plain and brief, but they are the crystallization of many years of my experience and research. You ll explore fundamental questions Will the catalyst particles be able to participate in the electrochemical reaction if they are fully covered by a thin ionomer film What can the limiting current density be based on the mass transport of air How severe will the voltage loss be if a thin layer of liquid water forms How can you quickly assess catalytic activity difference based on voltage difference in V-I curves How can a direct methanol fuel cell work using neat methanol How high can H2and O2 gases be pressurized within a PEM electrolyzer ... 

For the electrochemical characterization, V(i) curves were recorded and an IR correction was used to compensate for the ohmic losses in the measured potential (the ohmic resistance was measured by current interruption). The slope of the V(i) curve (the surface-specific conductivity) was calculated as a characteristic parameter for the electrochemical performance of the anodes and the cathodes. 

A neon bulb is a "gas tube diode," in which an electron avalanche takes place in a partial vacuum containing a small amount of the element neon. There is no difference between the two electrodes, so the same V-I curve is followed in both... 

In high-temperature fuel cells, the activation-related losses are often much less significant, and hence the characteristic concave portion of the V-I curve is hard to distinguish. In addition, as transport-related losses play a more important role, the convex portion of the curve often extends further to the left. 

Experimentally, there are several ways to determine the ohmic cell resistance. If the V-I curve has a substantial linear portion (in the center), the slope of this curve usually closely approximates the ASR of the cell. Only in such a linear portion of the V-I curve the ohmic resistance is dominant, and hence the determination of the ASR valid. Sometimes, a more accurate way to determine the ohmic resistance is from impedance spectroscopy. In an impedance spectrum of a fuel cell, the ohmic resistance is the real value of the impedance of the point for which the imaginary impedance is zero (Figure 2-5). As can be seen in the example, the ohmic resistance is invariant with gas concentration. The part of the impedance that is related to mass transport and kinetics, however, changes markedly with anode feed composition. 

Vernon et al The cell construction is shown in Figure 15 it has a barrier consisting of an initial 40-50 A cromium film covered by a similar thickness of either copper or silver to enhance film conductivity. The contact grid is ly t ick aluminium and the insulator a thermally grown oxide 15 A. A typical V-I curve for a 1.75 cm cell is shown in Figure 16. 

The effect of membrane thickness on DMFC performance for three different methanol feed concentrations (1.0, 5.0, and 10.0 M) is shown in Fig. 14.6. A 215- jm membrane is much more sensitive to increases in methanol feed concentration (a more significant downshift in the V-i curves with methanol concentration) than the thicker membranes (420 and 540 pm). The V-i curves for the 540 pm Nafion were nearly independent of methanol feed concentration (indicating that methanol crossover was small), but were suppressed as compared with those with a thinner Nafion film due to a high IR drop. 

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