FUEL CELLS—ENERGY FOR A POWER-HUNGRY WORLD - Chemistry: Notable Research and Discoveries - page 138

reactions, for example, when they chemically treat certain metal ores to
extract the metal—the result is a purer metal, which reduces the mass
of the original ore.
The transfer of electrons sets up an electric current—a flow of elec-
tric charges. This flow is vital in electrochemical reactions. As the reac-
tion continues, electrons are injected into the process and then drawn
off. Chemists carry out electrochemical reactions within a device known
as an electrochemical cell, with electrical conductors called electrodes to
inject and withdraw electrons.
An electrochemical cell should not be confused with a biological
cell, which is the basic unit of life. Electrochemical cells contain chemi-
cal solutions and electrodes to conduct electrons. As shown in the figure
on page 136, both oxidation and reduction reactions occur in the cell,
but these reactions are separated. Separation is essential so that elec-
trons can flow through electrodes and into attached wires, which can
be routed to wherever electricity is needed. To maintain electrical bal-
ance at the electrodes—in other words, to complete the circuit so that
electricity flows in a loop—an electrolyte allows the flow of ions between
the two halves of the system. This cell produces electricity and is called a
voltaic cell. The reaction proceeds as long as the materials last.
In contrast to a voltaic cell, electrolysis is a type of electrochemical
reaction in which electricity is the driving force rather than the product.
These reactions occur only with an energy input, as provided by the
electric current. In electrolytic cells, the electrodes would be attached to
some sort of electric generator to push electrons through the cell. For
example, electrolysis of water (H 2 O) is a reaction in which the compo-
nents, hydrogen and oxygen, are released. ( Lysis is a term derived from
a Greek word meaning to loosen or break apart. Electrolysis is the pro-
cess by which electricity breaks apart a compound such as water.)
Electrodes in a voltaic cell, however, are connected to circuits—
paths by which electrons flow. Voltaic cells are sources of electricity, so
they can be used to drive electrolytic reactions or perform other activi-
ties that require electricity. The term voltaic honors the Italian scientist
Alessandro Volta (1745-1827), a pioneer of electrochemistry. A simple
voltaic cell can form a battery, invented by Volta in 1800. The unit of
electric potential, the volt, also honors Volta.
Batteries are needed to power small, portable instruments such as
flashlights, cameras, and computers. In many flashlight batteries, the
two electrodes—attached to the plus and minus ends of the battery—