If we were to take a fuel cell to bits, we would see that it is mechanically very simple. Take a peek at Figure 17-2.
We can see that the fuel cell has two end plates. These are used as a casing for the fuel cell. They help contain the internal elements; furthermore, they provide an interface to the connection for hydrogen and oxygen gas.
Next up are the electrodes. These are the pieces that allow us to "tap off" electricity. They are
Gas outlet port Figure 17-2 Fuel cell construction.
generally made from stainless steel, as it does not react with the chemicals present. The stainless steel is perforated to allow the gas to penetrate.
The next assembly of carbon cloth/paper and Nafion membrane is termed an MEA, or membrane electrode assembly. This is the bit that makes the reaction take place that produces the energy.
Next we have a carbon cloth or paper. The gas can permeate this quite easily, one side—the side that interfaces with the Nafion membrane (more on that later)—contains a quantity of platinum which acts as a catalyst for the reaction that will take place next.
Now the Nafion membrane—but first a little explanation!
For those of you who were wondering, Nafion is a sulfonated tetrafluoroethylene copolymer. Are you any the wiser? Well Nafion is a special kind of u
plastic developed by DuPont in the 1960s. It's very special properties are essential to the operation of the PEM fuel cell. Essentially, what happens is that electrons cannot pass through the Nafion membrane but protons can. The platinum on the carbon cloth facilitates the separation of the electrons from the protons in the hydrogen atom. The protons are allowed to pass through the membrane; however, the electrons can't get through. Instead, they take the next easiest route.
The carbon cloth acts as a conductor. It allows the electrons to find a path to the stainless steel mesh. The mesh forms the electrode, which is connected to the circuit that the fuel cell powers. The circuit presents the route of least resistance, so the electrons make their way through the circuit. As they do this they perform some useful work which we can harness.
On the other side of the Nafion membrane is a mirror image assembly, with another set of carbon cloth, stainless steel electrode, and end plate.
At the other side, the electrons are reunited with the protons that have passed through the membrane, and the all-essential oxygen. The protons, electrons, and oxygen combine to form H2O— better known as water.
We will look at this process in more detail later, but first let's get on with generating some hydrogen!
Project 45: Generating Hydrogen Using Solar Energy
You will need
• PEM reversible fuel cell (Fuel Cell Store part no. 632000)
• Photovoltaic solar cell (Fuel Cell Store part no. 621500)
• Gas storage tank (2 x) (Fuel Cell Store part no. 560207)
• Rubber tubing
• Distilled water (not just purified!)
• Crocodile clip leads
Fuel cell tech spec
PEM reversible fuel cell 2 x 2 x 1/2 in. (5 x 5 x 12.5 cm) 2.4 oz. (68 grams) 0.95 volts open circuit 350 MA
In this project, we are going to look at the potential for a solar-hydrogen economy.
We are going to start with a simple experiment to generate hydrogen using a solar cell to provide the electricity to electrolyze water.
Familiarizing ourselves with the stuff!
If you have bought the items above, the chances are that you have got a lot of cool stuff, but are none too sure what to do with it. Don't panic!
We are going to look at what the stuff does, and how it all goes together in this section.
First is our fuel cell, shown in Figures 17-3 to 17-5.
First of all, you should note two terminals on the top—one red, one black. It should be apparent that these are the supply terminals for the fuel cell. Then, if we look on either side of the fuel cell, we see that there are intake pipes for gas. There should be two, these are diagonally offset in the fuel cell specified above.
You will see that one side of the fuel cell has a label "H2," this is the hydrogen side; the other side has the label "O2," this is where the oxygen goes.
The fuel cell comes supplied with some little caps as shown in Figure 17-3. These can be used to prevent water from escaping. These caps can be removed if desired, and two little plastic tubes are exposed for connection to the gas tanks (more about this later). Small lengths of rubber
tube are shown attached to the fuel cell in Figure 17-5.
Next we have the "gas tanks" shown in Figures 17-6 and 17-7.
We can see how in the first instance we fill the gas tanks with water—this is illustrated in Figure 17-6. Then, as shown in Figure 17-7, as our fuel cells produce gas, the gas displaces the water
which goes into the top half of the cylinder. The weight of this body of water acting on the gas provides a little pressure on the gas—enough to speed its return to the fuel cell.
We also connect the other pipe to the tank to enable the excess water to return.
The fuel cell is connected mechanically as in Figure 17-8. Note that the oxygen feed is connected in the same manner as the hydrogen.
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Figure 17-8 How to connect the pipes to the fuel cell.
Figure 17-8 How to connect the pipes to the fuel cell.
Before we can electrolyze water, we need to prime the fuel cell with water so that it has something to electrolyze. For this, we will be using distilled water. It is important that the water that you use is "distilled water," which should be readily available from the drug store, not just "purified" water. Water from the tap, even water from the chiller, contains trace elements that have the potential to wreak havoc with the delicate little MEA inside our PEM fuel cell.
First of all, you need to prime the fuel cell with water. A syringe and some small bore rubber tubing helps you accomplish this easily. Fill the fuel cell through one of the holes, allowing air to escape from the other. Once you have done this, put the caps back on the gas intake tubes of the fuel cell to prevent any ingress of air.
Fill the gas cylinders with water as well, and then connect it all up as shown in Figure 17-8. If there are any little gas bubbles trapped in the pipes, these must be bled out of the system first of all.
Now we come to connecting our solar cell.
Once the "mechanical engineering" is complete, we need to work on the "electrical engineering." Luckily, connection is very simple indeed. Take a peek at Figure 17-9 which shows how it is done.
Logic should tell you that the red terminal on the fuel cell is positive and the black terminal is negative. Use your crocodile leads to connect things up and put your solar cell somewhere where it will receive good light.
Don't hold your breath, the process is going to take a little bit of time! Over time you should observe a number of things happening. Gas will begin to form, and is collected in the two cylinders, displacing the water as it does so. You will notice that twice as much hydrogen is produced as is oxygen.
What is happening here?
The chemical symbol for water is H2O. Those with even a smattering of knowledge of chemistry will know that this means a water molecule is comprised of two hydrogen atoms and one oxygen atom.
When we pass an electrical current through the water, using the reversible fuel cell as our electrolyzer, we are splitting the water into its constituent parts—hydrogen and oxygen.
Because of the membrane inside the fuel cell, the hydrogen and oxygen are kept separated. The hydrogen and oxygen can then be piped off, and stored in tanks, where the hydrogen and oxygen can be saved for later use.
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Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.