2009년 10월 24일 토요일
SIMPLE AIR BATTERY(ZN) 만드는 방법
THE FUEL CELL
What is a fuel cell? It is an electrochemical device for converting the chemical energy in fuels directly into elecricity.
Why is it of high interest to scientists today? It can operate with two or three times the efficiency of other fuel-burning power producers. Thus the fuel cell, although not an energy source in itself, could help make our present fuel supply last years longer than expected.
Many scientists see the fuel cell playing a major role someday in providing electricity for automobiles and homes. Even now, large fuel cell systems are being developed for use as power plants for shopping centers and commuter trains. Small systems have already been used successfully in spacecraft.
In many ways, the fuel cell is like a battery. It contains no moving parts, is quiet, and wastes no energy as heat. Furthermore, it gives off no fumes. And like a battery, it has electrodes and an electrolyte.
But unlike a battery, the fuel cell will continue to produce electricity as long as fuel and an oxidant, such as air or oxygen, can be fed to the electrodes. In most batteries, one of the electrodes serves as the fuel and gets used up during operation. The fuel cell뭩 electrodes never get used up. Only the fuel.
There are several types of fuel cells. Some use hydrogen as a fuel. Others use ammonia, alcohol, or various hydrocarbon fuels. But even though they may work differently, they all achieve the same result: They all produce electricity directly from fuels in an efficient manner.
Through research, fuel cell power plants could prove to be an environmentally safe yet competitive means of producing electricity in the future.
Making a 밊uel Cell� *
THINGS YOU NEED: A nonmetallic mesh tube, such as a woman뭩 plastic hair roller, measuring about 3" long by 1" in diameter (see drawing). Three small rubber bands or some string. Thin sheet of zinc or galvanized steel 3½" by 2". A large gauze pad (see text). A tablespoon or so of natural powdered graphite (one tube of powdered graphite lubricant should do the trick). Flour. Salt. A saucer. Galvanometer from Experiment 2.
Making a fuel cell would be easy if we had the right mate- rials. Trouble is, the right materials are either dangerous or difficult to get in small quantities. So let뭩 take an easier path. Let뭩 build a device that is considered to be a form of fuel cell. It uses zinc as the fuel (one electrode), air as the oxidant (the other electrode), and salt water as the electro- lyte.
First pour all the graphite into a small mixing container. Next, in a separate container, prepare a binder of 1 part flour and 4 parts water. Then add the binder to the graphite, a little at a time, and stir. What we want to do is end up with a thick paste, like peanut butter.
Now from the gauze pad cut two strips as wide as the mesh tube (hair roller) and about 7" long. If you don뭪 have gauze, try a paper towel; fold it in four layers and cut it to size.
* The device in this experiment was designed by research scientist Hiry West of the McGraw-Edison Co., Bloomfield, N.J.
On a portion of one of these strips, spread all the graphite paste (messy, isn뭪 it?). You need cover only the first 3" of length, but cover the entire width of this 3" portion. Then place the mesh tube on the graphite and wrap the strip around the tube. The graphite will be facing the meshwork, of course.
Put the rubber bands or string around the gauze, and set the unit aside to dry (overnight, at least). That takes care of the air electrode for our 밼uel cell.� You may be wondering what part the graphite plays in the air electrode. Without getting too technical, it allows the oxygen in the air to enter the electrochemical reaction.
For the zinc electrode, roll the length of the zinc or galvanized steel into the tube small enough to fit inside the air electrode (but don뭪 insert it yet). Then wrap the second gauze strip around the zinc.
After the air electrode has had a chance to dry out, insert the wrapped zinc electrode into the tube core. It should be a snug fit.
We will need an electrolyte. So dissolve a tablespoon of salt in two or three tablespoons of hot water, and pour this electrolyte into a saucer. That completes all the preparations for the fuel cell. Now, will it work? Let뭩 see.
Clip one of the alligator clamps from the galvanometer to the top of the zinc electrode. Clip the other clamp to the graphite on the air electrode. The clamp must contact the graphite. You may have to cut away some of the gauze to ensure such contact.
Arrange the galvanometer as indicated in Experiments 2 and 3. Then stand the fuel cell in the saucer. As the salt water soaks into the gauze, electrochemical action should start. It does! The deflecting galvanometer needle proves that electricity is being generated.
Depending on how you made the fuel cells, needle deflection may or may not be large. But any movement at all proves the point. Interchanging the galvanometer connections to the fuel cell may make the deflection more noticeable.