Page 158 - Materials Chemistry, Second Edition

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2.4. The Amorphous State

O 2 H 2
4e -
2e -
O 2 2H 2

2O - 4H +
2H O
2
Cathode Anode
(reduction) (Oxidation)

Electrolyte
Membrane

Catalyst

Figure 2.100. Illustration of the operation of proton exchange membrane (PEM) fuel cell. In this design,
the electrolyte facilitates the transfer of protons across its membrane.

Table 2.14. Comparative Data for Fuel Cells
Fuel cell Operating temperature ( C) Efficiency (%) Output current (kW)

Alkaline 100–200 70 0.3–5
Polymer 80 40–50 50–250
Phosphoric acid 150–200 40–80 200–11,000
Molten carbonate 650 60–80 2,000+
Solid oxide 800–1,000+ 60 100

are yet cheap/efficient enough to widely replace traditional ways of generating
power, such as coal- and natural gas-fired, hydroelectric, or nuclear power plants.
Fuel cells are currently being tested and marketed for the replacement of traditional
internal combustion engines in automobiles. The high efficiencies and low emis-
sions of fuel cells are extremely intriguing, but problems with emission-free pro-
duction, and safe storage of hydrogen gas remain the primary stumbling blocks for
widespread incorporation of this technology.
Alkaline fuel cells have been used the longest, since the 1960s by NASA for space
shuttles. In fact, this application illustrates the utility of fuel cells. Hydrogen and
oxygen gases are used to power the fuel cell, which powered the electrical compo-
nents of the space shuttle. Water, the only byproduct of the reaction, was used as
onboard drinking water for the crew. Although AFCs are the most inexpensive