Page 282 - Alternative Energy Systems in Building Design

256 FUEL CELL TECHNOLOGY

Figure 7.4 Hydrogen
extraction by electrolysis.

■ 18.7 percent from natural gas
■ 6.5 percent hydroelectricity
■ 3 percent from petroleum
■ 2.8 percent from geothermal, solar, and biomass

As mentioned earlier, hydrogen production through electrolysis requires electrical
power, most of which is derived from the energy sources listed above.
Even though hydrogen fuel cells, when operating, emit only heat and water as
waste, significant pollution is caused when using electricity generated by fossil fuels
during the hydrolysis process. The only way to reduce the carbon footprint of the elec-
trolysis process is to use electricity produced by hydroelectric dams and geothermal,
solar, wind, or other clean power sources. Therefore, hydrogen fuel is only as clean as
the energy sources used to produce it.
In recent years, low-temperature fuel cells use specially designed proton-exchange
membranes that allow them to use methanol as fuel. In order to reduce the cost of
polymer electrolyte membranes, Brookhaven National Laboratory recently has devel-
oped a membrane coated with gold-palladium as a substitute for platinum, which is
cheaper to manufacture and less susceptible to poisoning.

HYDROGEN PRODUCTION
Molecular hydrogen is not available in nature. Hydrogen is an atmospheric trace gas
with a mixing ratio of 500 ppb by volume of air. In nature, hydrogen is produced and
consumed by microbes and methanogen organisms, which constitute a rapid biologic
hydrogen cycle. On earth, hydrogen is bonded to oxygen, forming bodies of water. At
present, hydrogen is produced most economically through the use of fossil fuels such
as methane. Hydrogen is also produced by a process referred to as steam re-forming,
or the partial oxidation of coal. The production of hydrogen by hydrolysis, discussed