Space fuel cells

M. Schautz, G. Dudley, Testing of Space fuel cells at ESTEC reprinted article from ESA Bulletin no. 60, 1992. 

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. 

Space—Fuel cells continue to be used in the U.S. Space Program, providing power on the space orbiters. Although this proven technology is of the alkaline type, NASA announced plans to use PEM fuel cells in the future. 

The cost of MEAs for applications up to 1 kW is commercially acceptable to the fuel cell industry today. The focus of MEAs for power applications greater then 1 kW, approaching 10-50 kW for stationary power (a typical space fuel cell is 15-30 kW and 75-100 kW for automotive fuel cells), is to drive the cost of the MEA lower by a factor of 10. This will be accomplished by developing the technology for manufacturing MEAs in a low cost, continuous lamination process and by finding alternate catalyst materials to platinum. 

Typical polarization curves for alkaline fuel cells are shown in Fig, 27-63, It is apparent that the all aline fuel cell can operate at about 0,9 and 5()() rnA/cnr current density. This corresponds to an energy conversion efficiency of about 60 percent IIII, The space shuttle orbiter powder module consists of three separate units, each measuring 0,35 by 0,38 by I rn (14 by 15 by 40 in), weighing 119 kg (262 lb), and generating 15 kW of powder. The powder density is about 100 W/L and the specific powder, 100 W/kg,... 

It is expected that the fuel cell should be able to compete with an IC engine in terms of size and weight. As an added advantage, many fuel cell components can be configured into a relatively wide array of shapes to take advantage of space onboard the vehicle. 

Although the principle of fuel cells has been known since 1838, practical applications arc fairly recent. The first applications were in the space program, where fuel cells powered the Gemini and Apollo spacecraft. In the 1960s and 1970s, fuel cells... 

Perhaps the ultimate combined appliances, which are currently under development, will he microturbines or fuel cell power generators used as small-scale co-generation systems. These would supply not only electricity, but space and water heating as well. 

Finally, the energy available from the above reaction might be used to operate a fuel cell such as those involved in the space program. In that case, as much as 818 kj/mol of useful electrical work could be obtained relatively litde heat is evolved. Summarizing this discussion in terms of an energy balance (per mole of methane reacting) ... 

A fuel cell is a voltaic cell in which a fuel, usually hydrogen, is oxidized at the anode. At the cathode, oxygen is reduced. The reaction taking place in the alkaline fuel cells used in the space program since the 1960s is... 

Stoichiometry has important practical applications, such as predicting how much product can be formed in a reaction. For example, in the space shuttle fuel cell, oxygen reacts with hydrogen to produce water, which is used for life support (Fig. L.l). Let s look at the calculation space shuttle engineers would have to do to find out how much water is formed when 0.25 mol 02 reacts with hydrogen gas. 

FIGURE L.l One of the three hydrogen-oxygen fuel cells used on the space shuttle to provide life-support electricity and drinking water. 

Self-Test 4.12B The reaction of H2 and 02 gases to produce liquid H20 is used in fuel cells on the space shuttles to provide electricity. What mass of water is produced in the reaction of 100.0 L of oxygen stored at 25°C and 1.00 atm ... 

The problem was solved by Francis Bacon, a British scientist and engineer, who developed an idea proposed by Sir William Grove in 18.39. A fuel cell generates electricity directly from a chemical reaction, as in a battery, but uses reactants that are supplied continuously, as in an engine. A fuel cell that runs on hydrogen and oxygen is currently installed on the space shuttle (see Fig. L.l). An advantage of this fuel cell is that the only product of the cell reaction, water, can be used for life support. 

The hydrogen-oxygen cell used in the space shuttle is called an alkali fuel cell, because it has an alkaline electrolyte ... 

Alkali fuel cells containing KOH and platinum- and gold-coated electrodes were developed for the space program, but these are too expensive for down-to-earth vehicles. In addition, these cells require pure oxygen rather than CO2 -containing air. 

The fuel eell is a nineteenth eentuiy invention in the twentieth eentury it heeame the heart of an eleetroehemical power plant and power souree, whieh is now in a stage of advaneed technology development. Its first and only applieation since the early 1960s, has been as an auxiliary power souree for spaee flights by the National Aeronautics and Space Administration (NASA). During the past decade, development for terrestrial (eivihan and defense) applieations has led to its commercialization and research on utilization in a variety of applications. Programs in the United States, Japan, Europe, and some other eoimtries are focused on the development of fuel cell power plant/power sources for (1) base-load,... 

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