[MUSIC] 20 years ago there was a lot of talk about a hydrogen economy. Somehow instead of having gasoline filling stations dotting the highways, we'd have hydrogen stations. And your cars would fill up with hydrogen. The only waste products being water. No pollution, no environmental concerns, wonderful. Until you realize that you can't just dig up hydrogen from the ground, hydrogen has to be made. And to make it, it takes energy. So you still need to use coal or natural gas, or oil, or nuclear power, or some energy source to take water and split it apart into hydrogen. Then, you could ship that hydrogen around, store it places, and use it in cars that use fuel cells. Well, I don't think a hydrogen economy is going to happen. Plugin hybrid cars, electric vehicles, are a much more sensible way to be able to substitute electricity for our transportation system. But fuel cells do have a place. So first, let me explain what a fuel cell is. So one of the simplest fuel cells is the permeable membrane fuel cell. And basically it has a membrane, and this membrane is treated with some type of catalyst, typically palladium. And palladium is pretty wonderful stuff. Because if I take a hydrogen molecule, and that hydrogen molecule wanders up here, it splits into hydrogen atoms, which of course are just protons. And on this surface, you'd have a very large concentration of hydrogen. Palladium, it turns out, is transparent to hydrogen. Hydrogen goes right through it. So you might think, aha, the whole thing's going to be filled with hydrogen. Well, atoms move when there's a gradient. If there's higher concentration on this side, then that side indeed hydrogen will go through. How do we create that gradient? How do we take away the hydrogen on this side? Well, if you add oxygen. Basically if you add air from this side. As the hydrogen comes through, you'll have the reaction of two hydrogens plus an oxygen going to water. You will have reconstituted this hydrogen gas into water. And we will have a concentration gradient across this membrane forcing the hydrogen to go through. As the hydrogen ions go through, the electron of course is siphoned off. And you get light bulb or some other electric use. This is the basic operation of a fuel cell. The demo that you see here in class is one of using a hydrogen fuel cell. And the first thing we have to do is create hydrogen and oxygen. These cells can run backwards. So if I take a battery and run the cell backward, I will take water and turn it back into hydrogen and oxygen. And that's what you see happening here in the demonstration. Once you can build off enough hydrogen and oxygen, you can take the two electrodes from the membrane, the fuel cell, and connect them to an electric motor. And voila, the tires on the car move. In this manner, we are still, quote, burning hydrogen. We're taking hydrogen, combining with oxygen and making water. But there's no flame. There's no explosion. There's no rocket fuel going on here. It's done in a solid device at room temperature in a very safe, complete manner. The problem with them, of course, is the hydrogen content in the first place. We can imagine that this is your electric circuit. You see, fuel cells make electricity. What happens is that you, I've gotta get my knot here, all right. This coming up here. Is that if you add hydrogen on one side hydrogen, if you recall, is a proton, right? The nucleus, with an electron going around it, that's the knot. Now if you make this out of the right stuff like palladium, right, some type of precious metal, that's really transparent to hydrogen. The hydrogen comes in and the hydrogen can freely go back and forth through this piece of metal. It's really amazing. If you're ever trying to purify, I've seen this in James Bond movies. When they're like, I've got to put the tritium in the nuclear bomb. But the key is, there's this metal palladium and hydrogen gas goes right through it, like it's not even there. Which is hard to believe because you can't walk through a wall. But hydrogen walks through palladium. So the question is, is why the hydrogen go through? Here's the key, we established a gradient. On this side of the membrane, we put a lot of hydrogen. And on this side of the membrane, we don't put any. Actually, we put air, which has oxygen in it. So, because there's a higher concentration of hydrogen on one side, the hydrogen molecule comes up. Palladium is a catalyst. It splits the molecule into two hydrogen atoms. The hydrogen atom goes right through the hole. Okay, good, and then it combines with oxygen on the other side making water, but the electron doesn't. The electron actually creates a voltage difference. The electron is left behind. So the electron can go through your circuit, right? Light up your lightbulb, run your electric car, power your office, do the nice things that electrons do. That's electricity, right? And then the return wire returns it to the other end. And when the hydrogen combines with the oxygen to make water on the other side, you get the electron back too. So basically, a hydrogen atom is a proton with an electron going around it. When you come up to the membrane, the hydrogen atom goes through and the electron goes on the wire. Very cool system. Here's a picture of a hydrogen fuel cell, a membrane hydrogen fuel cell, very much like the one I had in class. This one's hooked up to actually run a little fan. If we look in this, you can see PEM is the proton exchange membrane. You've got the flow plates, you've got a catalyst area, cathode catalyst where you're actually taking apart the hydrogen, or the water depending on what side of the direction you're running it. These systems are nice, but they're really toys. You need pure hydrogen to start with, which is a difficulty. And lifetime of these proton exchange membranes is not large. The capital costs would be much higher than the energy game that you would get from doing it. Let's look at the diagram again. Hydrogen in this case comes in, the fuel. The electrons go through the circuit. The hydrogens go through the Polymer Electrolyte, combine with oxygen from the air and making water. Thing is, you have to make that hydrogen. What if you could do a fuel cell that instead of using the hydrogen used natural gas? So, if I take natural gas, methane coming in, I now need something still, that's going to split out this hydrogen. To do that a proton exchange membrane will not work. I'm going to need to do something that's at a much higher temperature. There's a thing called a solid oxide fuel cell. And this can take methane, and it can split it up into the carbon and into the hydrogens. Of course, to be able to do that, it needs some thermal energy. These things are hot, 800 degrees Centigrade. Don't touch it. When I do this, I can split up the methane as a fuel. I can add air from the other side, right, of the oxygen. And I can do the same reaction we do for burning methane. Methane plus oxygen going to carbon dioxide plus water. This reaction will take place without burning. No visible flames, warm indeed. But a solid oxide fuel cell can do the conversion all the way to electricity at 50%. A natural gas power plant that just uses steam cycle would be at something like 33%. A combined cycle natural gas system where first it runs a turbine that with the exhaust and that turbine turns a generator. The excess heat boils water that turns another turbine which turns a generator. That can get the 40% efficient. This fuel cell with basically no moving parts just sits there. Sucks in methane and air puts out a little bit of carbon dioxide, a little bit of water vapor. In fact, most of the water vapor is recycled. Can run at 50%. The advantage of having a fuel cell energy system is that you have no moving parts, no flame. And it can be done in a manner, such that Bloom Energy did, where you don't even need any precious metal catalysts. You just take many, many of these stacks. And they put on the electrodes with ink and they stack these things up, seal them, and they say they'll last for ten years. Here's some what they look like. Each of these units can make 100 kilowatts of electricity like a giant battery. Now you have put in fuel, you have to buy the natural gases though. Today, that's actually quite economical. So here we have a number of them in the lab. So what about the economics? How much does a bloom box cost? It costs well over $1 million unless you happen to be in a state that says, hey, people, please buy these. Just like there are economic incentives to buy a hybrid car, governments can decide that in certain locations. Particularly, California in the United States, the electric grid needs more power. And it's been very difficult to build new power plants. So many systems are designed to really subsidize people to put solar cells on their roofs or industries to buy fuel cell systems. In California, you can buy a 100 kilowatt electric unit, it actually makes 100,000 watts for $750,000. Is this a good deal? Well, let's figure out how many cents per kilowatt hour this is. One of the questions you always have to ask and we did this similarly when we tried to analyze a windmill is how long will it last? How long before the fuel cell breaks? They're saying ten years. So let's use ten years because after all what we want is cents per kilowatt hour, kilowatt time unit, an energy unit. We just need to do a little conversion. One year is 8,760 hours. So the years cancel. This would now be dollars per kilowatt hour. If I multiply this out, it turns out to be $0.085 per kilowatt hour of electricity. That's the capital cost. You still have to buy the methane. At today's prices, though and the amount of methane this needs, is very small. Maybe an additional penny per kilowatt hour. In many places in the US, a wholesale cost of electricity is still $0.03 or $0.04 per kilowatt hour. In which case buying your own bloom box probably would not make sense. In places like California, where the cheapest rate you can get is $0.12 per kilowatt hour, these things are going like hotcakes. Fuel cells have the advantage that you're not part of the grid. And, just like anything else, you could turn it on or off. There's some startup time. The whole thing has to warm up. After all, it runs at 800 degrees centigrade. But you can turn it off and not use it for a time period, if that's your druthers. Otherwise, you can use this system and it becomes quite economical. So in some locations, if the retail cost of electricity is very high, you still have a relatively low cost of natural gas, making your own box, your own bloom box, makes a lot of economic senses. That's what you need to know about fuel cells. [MUSIC]
