Alkaline fuel cells pressure

Therefore, scrubbing is often required. The scrubbing process is not tolerant of water contamination because it can cause the bed to collapse if exposed for prolonged periods to high water vapor pressures or to condensation. Alkaline fuel cells also require the removal of carbon oxides including C02. 

Fig. 13.17. Performance of advanced lightweight pressurized alkaline fuel cells. The dashed lines show initial advanced AFC cell results. A, 149 °C, 17 bar B, 140 °C, 17 bar C, 127 °C, 17 bar D, 110 °C, 4 bar E, 82°C, 4 bar F, 82 °C, 1 bar G, 0.2 MgPt-C and the same conditions as F (IR-free) H, 10 mg/cm2 Au/Pt, 127 °C, 1 bar (IR-free). , nominal performance of space shuttle cell (1000 h) , United Technologies target goal (1000 hr). Solid lines show solid polymer electrolyte cells for comparison under different pressure and temperature conditions. (Reprinted from Assessment of Research Needs for Advanced Fuel Cells, S. S. Penner, ed., Pergamon Press, 1986, pp. 14,87.)...

Fig. 13.27. Potential vs. current density plots for state-of-the-art fuel cells, o, proton exchange membrane fuel cell , solid oxide fuel cell , pressurized phosphonic acid fuel cell (PAFC) a, direct methanol fuel cell, direct methanol PAFC , alkaline fuel cell. (Reprinted from M. A. Parthasarathy, S. Srinivasan, and A. J. Appleby, Electrode Kinetics of Oxygen Reduction at Carbon-Supported and Un-supported Platinum Microcrystal-lite/Nafion Interfaces, J. Electroanalytical Chem. 339 101-121, copyright 1992, p. 103, Fig. 1, with permission from Elsevier Science.)...

Hydrogen was the only really useful non-exotic fuel, but using it with relatively inexpensive nickel catalysts in an alkaline fuel cell required high temperatures and pressures, costly pressure vessels, and ancillary equipment. 

Fuel cells must carry the costs of conditioning the two reactant gases as well as their own capital charges. Hydrogen requires transport to the anode side of the fuel cells. This is usually by rotary blower, but it also should be possible to operate membrane cells at some positive pressure and then to deliver the hydrogen without mechanical aid. The temperature and water content of the hydrogen must be considered in the overall heat and mass balance. Air and oxygen are candidates for use at the cathodes. The classical balance between cost and efficiency determines the choice. Wth alkaline fuel cells, the carbon dioxide in the air is of concern. It can consume the hydroxide value and contaminate the end product. It is possible to scrub the air to remove the CO2 before... 

The technology of choice for on-board electric power on mid-length space vehicle missions (several days to a year), including the important man-moon mission, was the fuel cell. This was because the use of batteries for more than a couple of days proved too heavy, combustion engines and gas turbines required too heavy a fuel supply, and the use of a nuclear reactor was only suitable for missions of a year or more. There was a simple choice of fuel for space fuel cells it was hydrogen because it doesn t require a fuel processor other than storage and pressurization, it is relatively lightweight when stored under pressure, and it was the best fuel for the early-developed alkaline fuel cell. Fuel flexibility was not an issue. 

To supply the library, four independent photovoltaic fields, each with a particular orientation due to the architecture of the building, were installed. The first significant level of storage in lead batteries ensured a few days of autonomy, and seasonal storage was done with an alkaline electrolyzer, pressurized gas tanks and an alkaline fuel cell. The characteristics of the devices can be seen in the principle diagram (Figure 2.48). 

Historically, the major alkaline electrolyte fuel cells have operated at well above ambient pressure and temperature. The pressures and temperatures, together with information about the electrode catalyst, is given for a selection of important alkaline fuel cells in Table 5.1. 

We have already pointed out that alkaline fuel cells can be operated at a wide range of temperatures and pressures. It is also the case that their range of applications is quite restricted. The result of this is that there is no standard type of electrode for the AFC, and different approaches are taken depending on performance requirements, cost limits, operating temperature, and pressure. Different catalysts can also be used, but this does not necessarily affect the electrode structure. For example, platinum catalyst can be used with any of the main electrode structures described here. 

In the "PURE" project on the Shetland Islands, the wind-hydrogen system is composed of two wind generators of 15 kW power each, a 15 kW advanced alkaline electrolyzer operating at 55 bars, a 16-cylinder stack of 44 Nm3 H2 capacity at the same pressure, and a 5 kW PEM fuel cell [54],... 

In this section, details of an easily controllable, safe method for producing high-purity H2 gas are described. This method of generating H2 gas is particularly suitable for providing a clean source of H2 gas for use as an anodic fuel in fuel cells or as a fuel for internal combustion engines in transportation applications. This compact, portable H2 generator is based on a non-pressurized, aqueous solution of alkaline sodium borohydride (NaBH, tetrahydroborate). As found by Schlesinger et al.,1 when aqueous NaBH... 

Various combinations of applications, including different choices of photovoltaic panels and electrolysers were tested. The cumulative operating times logged for the various plant subsystems differed considerably according to the test programs run, ranging from 6000 h for the alkaline low-pressure electrolyser, to 2000 h for the membrane electrolyser, 5200 h for the catalytic heater, 3900 h for the PAFC fuel cell plant and 900 h for the LH2 filling station. 

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