Environmental Engineering Reference
In-Depth Information
vehicles (BEVs) with high efficiency but low driving range and short battery life
have limited market penetration at present. Increasing the performance of high-en-
ergy batteries for PHEVs could lead to the higher market penetration of BEVs. The
problem remains, of course, of generating electricity to charge the batteries; if this
electricity originates in fossil-fuel-generating plants, BEV usage will not achieve
much more than transferring the source of emissions from the vehicles (automo-
biles or trucks) to the electricity generating plants.
Fuel batteries or fuel cells produce energy by electrochemical means, as opposed
to the combustion processes in conventional engines. Hydrogen reacts chemically
with oxygen, forming water and generating electricity. There are fuel cells of dif-
ferent types; the main candidate to be used in automobiles is the one based on the
proton exchange membrane (also called solid polymer electrolyte fuel cell), due to
its lower cost, adequate size, simple design, and operation at low temperatures.
Fuel-cell batteries require hydrogen, which may be generated in the automobile
itself from ethanol, methanol, or natural gas.
Fuel cells are much more efficient than internal combustion engines and, as the
fuel is electrochemically converted, they do not emit pollutant gases. Widely used
in the United States space program, their high cost and size, until recently, hindered
their use in automobiles. Important innovations achieved in the last 10 years have
been changing this situation, making the cells one of the most promising technolo-
gies for the near future.
In 1859, the French physicist Gaston Planté invented the first lead-acid battery us-
ing two sheets of metal separated by a piece of linen and suspended in a glass jar
of a sulfuric acid solution. Batteries widely used today are essentially variations of
Planté's old invention.
The greatest advance in battery design since Planté occurred in the United States
in 1977. Exxon developed and commercialized the lithium-ion battery, which con-
sists of two electrodes separated by an electrolyte, often a polymer gel. When the
battery is being charged, lithium ions migrate from the positive electrode, which is
made from a lithium-based material, through the electrolyte to the negative elec-
trode, which is usually made of carbon. When it is discharging, the ions flow in an
