 This is a fuel cell, and a fuel cell is constructed by having a membrane right here, see, in this membrane. The membrane is a polymer layer that has carbon filament embedded with platinum, and that's acting as the catalyst. And what we're going to do is we're going to take the hydrogen that we're generating in our electrolysis, and hydrogen will be one of our fuels, and then we'll take the oxygen from the oxygen side, and we'll pass the oxygen into our fuel cell, and the hydrogen and oxygen will react to produce electricity. And we're going to measure that by just connecting our voltmeter to our fuel cell. Now notice we don't have any electrons coming into our fuel cell. The only thing we have is the hydrogen gas coming in on this side, and the oxygen gas coming in on this side. So I'm going to connect this so we can measure the voltage that's actually being produced. And one thing about a fuel cell is they're slow to come up to speed. It's not like your dry cell battery in which you suddenly have 1.5 volts. With a fuel cell, you'll notice that we're gradually increasing our voltage. So as the fuel cell begins to operate, it will take a few minutes for it to come up to its capacity. You can see now we're getting a higher voltage. We're now 0.7879. You should be able to use your standard reduction potential table to calculate the amount of energy that could actually be produced in this reaction, because you're taking hydrogen and oxygen and producing water. Now you see that we have reached 0.83 and something about 0.83 volts. It's going to vacillate back and forth between something like 0.82 and 0.83. I'd also like you to notice that if we stop our production of hydrogen, that the fuel cell will continue to operate for a few minutes. And then it will gradually, just like it took time for it to come up to speed, it will actually continue to discharge for several minutes before it's totally discharged.