 So, what is a fuel cell? Well, a fuel cell converts chemical energy from a fuel directly into electricity without combustion, so without burning. The electricity is produced constantly as long as fuel is being supplied to the electrodes. Let's look at a very simple example called a hydrogen-oxygen fuel cell. This is a hydrogen-oxygen fuel cell. They've been used for a long time in space exploration. The reason for that is one of the fuels to get up into space is hydrogen, and the crew require oxygen to breathe. So, you've got hydrogen and oxygen, so you can use those to make electricity. This is a fuel cell from an Apollo spacecraft that went to the moon. So, here's a picture of a hydrogen-oxygen fuel cell and a bit of an idea about how it works. You pump hydrogen in one side, use oxygen from the air in the other side. Now, the hydrogen splits and produces electrons. Those electrons travel through the external circuit, and you can use them to power something. Hydrogen travels through, hydrogen ions travel through, I should say. They regain their electrons on this side. They react to the oxygen from the air and you produce water vapor as a byproduct. Here's another picture of a hydrogen-oxygen fuel cell. So, hydrogen gas comes in one side, oxygen gas comes in the other. At the anode, you get the hydrogen splitting. Now, you get hydrogen ions traveling through the solution. You reunite with the oxygen on this side, and you get water being produced, and that's down here. In the middle, you have an electrolyte. So, in this case, it's potassium hydroxide that allows the hydrogen ions to travel from one side to the other. Here's an animation showing how a hydrogen-oxygen fuel cell works. Hydrogen coming in from this side, this is anode. Electrons are being stripped off of the hydrogen. The hydrogen ions pass through, and we get our water being produced on this side of the cathode. So, hydrogen-oxygen fuel cells have been investigated to be used in cars for a little while. Here is a Mercedes F-cell car. Here's an F-C fuel cell stack from a Toyota car. Ford got into the action, and here's a really small one. The size of these things can be large or small, depends on what you want to use them for. So, they have been in development for a while. So, here's the redox equations for the hydrogen-oxygen fuel cell. So, at the anode, you get the hydrogen being oxidized. This hydroxide here, that's the potassium hydroxide, the electrolyte we were looking at before. So, the hydrogen gas is oxidized, and you get electrons being generated. At the cathode, you're getting the reduction happening. So, the oxygen is being reduced to hydroxide ions. But the hydroxide ions cancel out over here. So, what you end up with is water being produced. So, the overall equation is you're reacting your hydrogen with your oxygen to produce water. So, it's like I said before, it's the same as combusting hydrogen and oxygen to produce water. But rather than generating heat to do that, we strip the electrons off in a separate reaction. There's another few different types of fuel cells. So, this is an aluminium air fuel cell. So, oxygen from the air is oxidizing aluminium. There's problems with this. One of the problems is you're essentially, well, you're using aluminium to generate electricity. You don't get the aluminium back. You know, readily available for that. And aluminium is very, very handy. It's one of the most widely used metals, and it's very, really, very easily recycled. So, this isn't used very often. So, another fuel cell is called the solid oxide fuel cell. A solid oxide fuel cell can use a variety of fuels, depending on what's available, really. I'm using oxygen on one side, like we had with the hydrogen oxygen fuel cell. Here, you can use hydrogen. You can use carbon monoxide. You can use methane. So, this one's handy in that a variety of fuels can be used. So, here's a picture showing the solid oxide fuel cell. So, in this case, we're using hydrogen and carbon monoxide as our fuel on one side, and just oxygen on the other. And again, so, at the anode, these are being stripped of their electrons. Those electrons are being used to generate the electricity over here. Well, they're generating the electricity as they flow. And as they return to the oxygen, you get your waste products being produced. This is a stack of fuel cells. Here is a large whole heap of fuel cells joined together to generate usable amounts of electricity that could supply a home or a business. So, they're stackable. The more fuel cells you have joined together, the more electricity you make. Here's an example of a stack that I was talking about. So, you have an interconnector, you have your anode, you have your electrolyte, and you have your cathode. These spaces allow for you to pump your fuels in. So, one fuel going one direction, one fuel going the other direction. And then, as they meet at that boundary between the anode, the electrolyte, and the cathode, that's where you get your electricity being produced. It's very porous. There's lots of holes with lots of space, and that's so you can have things like catalysts laid on the surface here. It allows the gasses to pass through as well because you get holes.