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The Fuel CellA
fuel cell is an electrochemical device which combines hydrogen fuel with oxygen
to produce electric power, heat and water. In many ways, the fuel cell resembles
a battery. Rather than applying a periodic recharge, a continuous supply of oxygen
and hydrogen is supplied from the outside. Oxygen is drawn from the air and hydrogen
is carried as a fuel in a pressurized container. As alternative fuel, methanol,
propane, butane and natural gas can be used.  The
fuel cell does not generate energy through burning; rather, it is based on an
electrochemical process. There are little or no harmful emissions. The only release
is clean water. In fact, the water is so pure that visitors to Vancouver’s Ballard
Power Systems, the leader in the development of the proton exchange membrane fuel
cell (PEMFC), drank clear water emitted from the tailpipes of buses powered by
a Ballard fuel cell. The fuel cell is twice as efficient in converting
fuel to energy through a chemical process than combustion. Hydrogen, the simplest
element consisting of one proton and one electron, is plentiful and is exceptionally
clean as a fuel. Hydrogen makes up 90 percent of the composition of the universe
and is the third most abundant element on the earth’s surface. Such a wealth of
fuel would provide an almost unlimited pool of energy at relatively low cost.
But there is a price to pay. The fuel cell core (or ‘stack’), which converts oxygen
and hydrogen to electricity, is expensive to build. Hydrogen must be carried
in a pressurized bottle. If propane, natural gas or diesel are used, a reformer
is needed to convert the fuel to hydrogen. Reformers for PEMFCs are bulky and
expensive. They start slowly and purification is required. Often the hydrogen
is delivered at low pressure and additional compression is required. Some fuel
efficiency is lost and a certain amount of pollution is produced. However, these
pollutants are typically 90 percent less than what comes from the tailpipe
of a car. The fuel cell concept was developed in 1839 by Sir William
Grove, a Welsh judge and gentleman scientist. The invention never took off, partly
because of the success of the internal combustion engine. It was not until the
second half of the 20th century when scientists learned how to better utilize
materials such as platinum and Teflon™, that the fuel cell could be put to
practical use.
A fuel cell can be thought of as electrolysis in reverse,
using two electrodes separated by an electrolyte. Hydrogen is presented to the
negative electrode (anode) and oxygen to the positive electrode (cathode). A catalyst
at the anode separates the hydrogen into positively charged hydrogen ions and
negatively charged electrons. On the PEM system, the hydrogen is catalyzed; the
smaller protons migrate across the membrane to the cathode where they combine
with oxygen to produce water and heat. The electrodes pick up the electrons to
produce an electric current. A single fuel cell produces 0.6 to 0.8V under load.
Several cells are connected in series to obtain higher voltages. The
first practical application of the fuel cell system was made in the 1960s during
the Gemini space program, when this power source was favored over nuclear or solar
power. The fuel cell, based on the alkaline system, generated electricity and
produced the astronauts’ drinking water. Commercial application of this power
source was prohibitive because of the high cost of materials. In the early 1990s,
improvements were made in stack design, which led to increased power densities
and reduced platinum loadings at the electrodes. High cost did not hinder
Dr. Karl Kordesch, the co-inventor of the alkaline battery, from converting
his car to an alkaline fuel cell in the early 1970s. Dr. Kordesch drove the
car for many years in Ohio, USA. The hydrogen tank was placed on the roof and
the trunk was utilized to store the fuel cell and back-up batteries. According
to Dr. Kordesch, there was “enough room for four people and a dog”. |
