Fuel cell current-voltage characteristics

Figure 14.10 gives a schematic presentation of the current-voltage characteristics of hydrogen and oxygen on platinum. The theoretical open circuit cell voltage at 25 °C and standard conditions is 1.229 V, for both the fuel cell and electrolyzer. 

Fig. 14.10 Current-voltage characteristics of hydrogen oxidation and oxygen reduction in a fuel cell, and hydrogen and oxygen evolution in an electrolyzer.

Fig. 2. Schematic current/voltage characteristic of a fuel cell...

The impregnation of porous nickel discs with CoPc was difficult because of the limited solubility of the chelate in the usual solvents. CoPc cathodes with carbon as substrate were therefore prepared for use in H2/O2 fuel cells. A mixture of 72 mg CoPc and 48 mg acetylene black, with PTFE as binder, was pressed into a nickel mesh of area 5 cm2. Electrodes of this type were tested in an H2/O2 fuel cell with 35% KOH electrolyte in an asbestos matrix at 80° C. Figure 5 compares the current/voltage characteristics of CoPc cathodes (14 mg/cm2) with those of other catalysts, including platinum (9 mg/cm2), silver (40 mg/cm2), and pure acetylene black (20 mg/cm2). An hydrogen electrode (9 mg Pt/cm2) was used as the anode in all tests. To facilitate comparison of the activity of different cathodes, the pure ohmic internal resistance of the cells (of the order of 0.02 ohm) was eliminated. 

It is further important to note that all the current/voltage characteristics depicted in Fig. 6 are unchanged by the presence of liquid fuels such as methanol, formaldehyde, formic acid, or hydrazine. The phthalocyanine electrode remains completely inert toward such substances. For this reason, no mixed potential can be formed at a phthalocyanine electrode, as for example can occur at a platinum electrode, when it is used as cathode in a methanol cell containing sulfuric acid. This is shown by a comparison (see Fig. 7) of the stationary characteristics of the platinum alloy we found to be the most active in the presence of methanol, namely a Raney ruthenium—rhodium electrode, with an iron phthalocyanine electrode, both measured in 4.5 N H2SO4+2M CH3OH. 

Figure 19.18. Data of electrochemical fuel cells, (a) Processes in a fuel cell based on the reaction between hydrogen and oxygen, (b) Voltage-current characteristic of a hydrogen-air fuel cell operating at 125°C with phosphoric acid electrolyte [Adlharl, in Energy Technology Handbook (Considine, Ed.), 1977, p. 4.61). (c) Theoretical voltages of fuel cell reactions over a range of temperatures, (d) Major electrochemical systems for fuel cells (Adlharl, in Considine, loc. cit., 1977, p. 4.62).

Subcell Approach Stumper et al.135 presented the subcell approach to measure localized currents and localized electrochemical activity in a fuel cell. In this method a number of subcells were situated in different locations along the cell s active area and each subcell was electrically isolated from each other and from the main cell. Separate load banks controlled each subcell. Figure 8 shows the subcells in both the cathode and anode flow field plates (the MEA also had such subcells). The current-voltage characteristics for the... 

Figure 12.2 Current-voltage characteristic obtained in a 50-cm dihydrogen/air fuel cell at 353 K at a total pressure of 150kPa. The anode and cathode layers consist of about 50wt% Pt/C [0.4/0.4mgp(/cm (anode/cathode)] and ionomer (ca. 900 EW ionomer/carbon ratio = 0.8 1). Circles, experimental data triangles, mass-transport-free AEceii squares, mass-transport-free and ohmically corrected AEceii- The current density is referred to the geometric surface area of the MEA. (From ref. 4, with permission from Elsevier.)...

Currenl Density/mA cm Fig. 8.4 Current-voltage characteristics of fuel cells and the associated losses. 

FIGURE 12.12 Current-voltage characteristics and power density curves of a PEM fuel cell with PVDF-g-PSSA having the same G (53%) and prepared with two different radiationgrafting methods. 

Fig. 18.9 (a) Current-voltage characteristics of 10 cm single H2/O2 fuel cells using dealloyed PtCua, dealloyed PtNia, and dealloyed PtCos cathode catalyst, in comparison with standard Pt cathode catalysts, (b) Pt-mass activities at 0.9 V of the dealloyed Pt-bimetallic cathode catalysts (reprint with permission from ref [47])... 

Electrochemical Characterization of Fuel Cells—Correlation Between EIS and Current/Voltage Characteristic of Fuel Cells. The performance of a fuel cell depends not only on electrochanical properties of the electrode/electrolyte... 

Sasaki K, Hori Y, Kikuchi R, Eguchi K, Ueno A, Takeuchi H, Aizawa M, Tsujimoto K, Tajiri H, Nishikawa H, Uchida Y (2002) Current-voltage characteristics and impedance analysis of solid oxide fuel cells for mixed H2 and CO gases. J Electrochem Soc 149(3) A227-A233... 

Sasaki K, Watanabe K, Teraoka Y (2004) Direct-alcohol solid oxide fuel cells current-voltage characteristics and fuel gas compositions. J Electrochem Soc 151(7) A965-A970... 

Conventional in situ analysis of fnel cells is limited in most cases to static and dynamic electrochanical methods, in particular to current-voltage characteristics and impedance spectroscopy or cyclovoltammetry. These techniques provide an integral type of information and cannot easily differentiate between cathode and anode. Aiming at complementary and more selective information, a fuel cell capable of operating in the resonator of an X-band spectrometer was developed (Fig. 16), which permits direct observation and monitoring of radical formation. This study had the objective to identify fuel cell operating conditions that lead to oxidative membrane degradation. 

Equations describing global properties of fuel cells are denoted as zerodimensional models. An example is the description of the current-voltage characteristics of a fuel cell where the different overvoltages are considered, for example, in the form (Ticianelli et al., 1988)... 

FIGURE 12.25. Current-voltage characteristics of monolithic single solid oxide fuel cell at 1000°C using pure... 

FIGURE 12.29. Current-voltage characteristics of a single planar cell (5x5 cm ). (From Van Berkel, F.P.F., Van Heuveln, F.H., and Huijmans, J.P.P., Proceedings of the Third International Symposium on Solid Oxide Fuel Cells, Singhal, S.C. and Iwahara, H., Eds., The Electrochemical Society, Pennington, NJ, 1993,744-751. With permission.)... 

Fig. 89. Current-voltage characteristic of a fuel cell with Zro.gs Cao.15 Oj.gs as solid electrolyte at 1000 °C for different fuel mixtures at the anode and oxygen at the cathode, a C3H8 H20 C02 = 1 3 1, b CaHg H20 C02 = 1 5 4, c H2 H20 = 35 1...

Fig. 1.3 Current-voltage characteristic of the fuel cell made by Mond and Langer in 1889. The cell surface was 42 cm. It is not currently known whether the data presented relate to air or oxygen as the oxidant (the researchers used it alternately) [7]...

In this paper we report the effect of varying loads on a small size DMFC stack (10 cells with 9 cm active-area each). The transient responses of the stack voltage have been investigated upon variable current load conditions to obtain the information on the dynamic characteristics of the stack. Also, the transient responses of the stack current upon changing fuel flow rates have been monitored to obtain the optimal operating conditions for the staek. 

Figure 2-2 Ideal and Actual Fuel Cell Voltage/Current Characteristic...

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