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Miniaturized Fuel Cells
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18343 |
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Section : |
NATURAL SCIENCE
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| Issue
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10 / 1990 |
2,310 Words |
| Author
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Christopher K. Dyer
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For portable, reliable electricity, the battery has been hard to beat. In its various forms the battery can be found everywhere, from toys to televisions, inside laptop computer and beneath the skin in implantable pacemakers.
But many kinds must be thrown away when their chemical energy is used up, and even the rechargeable versions have a limited life. In addition, mercury batteries developed for watches and other electronic circuits now cause disposal problems due to their toxicity.
Does an alternative to the battery exist as a source of portable electricity? The U.S. space program has depended for years on the fuel cell, which transforms the chemical energy of oxygen and hydrogen into electricity. These units have been far too expensive for commercial production, but recently scientists at Bell Communications Research discovered a way to miniaturize the fuel cell without reducing its energy capacity - paving the way for a host of new applications.
Batteries and Fuel Cells
The unfortunate characteristics of batteries that are unlikely to change are that the energy that they can store is quite limited, the recharging time required is inconvenient, and internal physical changes in the battery could require periodic replacement. Also, the cost of using "primary" (nonrechargeable) batteries could be prohibitive in high-use applications.
Some of these difficulties could be overcome by the use of a fuel cell, in which the considerable energy of the combination of hydrogen and oxygen is directly harnessed as electricity - and the only effluent from the process is remarkably pure water.
The principle was first demonstrated 150 years ago by Sir William Grove in England as a way of showing the convertibility of different forms of energy - in this case, chemical to electrical energy. He constructed such a cell in 1839 with hydrogen and oxygen reacting on platinum electrodes to produce electricity. It took almost 100 years for the technology to be applied, with the development of an electrical generator, later spurred on by the demand of the U.S. space program for nonpolluting power for spacecraft. Unfortunately this was not an inexpensive power source, particularly in small sizes. Lightweight and reliable fuel cells are possible, but their cost, if designed like those used by NASA, is prohibitive for commercial application.
An advantage to the user of a fuel cell is that it provides quiet, nonpolluting electrical power continuously, provided it is supplied with fuel and oxidizing gasses. Batteries need periodic recharging or replacing, depending on use, and although recharging replenishes their chemical energy, this is usually held in a solid form which undergoes physical change with each recharging cycle. This shortens their useful life to a few hundred recharges, or "cycles." A fuel cell, on the other hand, generates electricity without causing irreversible change to any of its parts. The two electrodes are catalysts that merely assist the release of electrons from molecules of a "fuel and cycle them as electric current without generating any heat.
In one common type of fuel cell, platinum electrodes mediate the transfer of
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