FUEL CELLS—ENERGY FOR A POWER-HUNGRY WORLD - Chemistry: Notable Research and Discoveries - page 137

Another problem is also looming. Earth is warming—surface tem-
peratures have increased about 1.33°F (0.745°C) in the last century. Sci-
entists of the Intergovernmental Panel on Climate Change issued a report
in 2007 and concluded, “Most of the observed increase in global average
temperatures since the mid-20th century is very likely due to the observed
increase in greenhouse gas concentrations.” These atmospheric green-
house gases, such as carbon dioxide, retain the planet's warmth, similar
to actions of a greenhouse, and elevates the temperature. (The term gas as
used here refers to a phase of matter, as in air.) This rise in temperature
may not seem like much, but the warming trend has been melting polar
ice. If the melting continues unabated, an alarming rise in sea level may
ensue, along with other drastic climate changes that occur when nature's
delicate balance is upset. Combustion of gasoline and similar fuels pro-
duces greenhouse gases such as carbon dioxide. Yet Earth's burgeoning
population and the essential economic development to support this pop-
ulation require increasing amounts of energy. To meet these needs while
maintaining the integrity of the environment, alternative sources of en-
ergy must be found. One alternative is an electrochemical device known
as a fuel cell, the subject of this chapter.
InTroduCTIon
Electrochemistry is the study of chemical reactions in which electric-
ity plays a role. Some electrochemical reactions generate electricity as
the reaction proceeds, while in other cases the opposite occurs—elec-
tricity drives the reaction. In either case, electrochemical reactions in-
volve the transfer of electrons, which are the negatively charged par-
ticles surrounding an atom's nucleus. Reactions in which electrons are
transferred (or appear to be transferred) from atom to atom are called
oxidation-reduction reactions.
An oxidation reaction is so named because it used to refer to chemi-
cal activities involving oxygen, such as combustion. The term combus-
tion is presently used in a broader sense, and it describes a process by
which an element increases its oxidation number. An oxidation num-
ber is an abstraction—chemists assign this number based on a set of
rules, which helps them understand reactions. Oxidation corresponds
to a loss of electrons. Reduction, on the other hand, corresponds to a
gain in electrons. Miners and metal producers have long used reduction