We've recently discovered a new method to generate electricity, called fuel cells, which is less expensive and more efficient than traditional power plants using radioactive materials like uranium. These new fuel cell plants don't use radioactive materials; instead, they use hydrogen to generate electricity. In other words, the fuel cells use the same fuel we have on hand. The hydrogen used in fuel cells comes from water. Every element in the periodic table can be combined with hydrogen to make a fuel, such as gasoline, butane, propane, diesel fuel, or jet fuel. The most commonly used fuel today is gasoline, which is made from carbon, hydrogen, and oxygen. But what if we used all the carbon atoms in gasoline as fuel to produce electricity? After all, water contains carbon and hydrogen in the form of carbon dioxide. If we could break apart those carbon dioxide atoms and remove the carbon, we would have the hydrogen we need to generate electricity. With only water and electricity, we could do this! It's so simple that I'll illustrate the process on the board. First, water is electrolyzed to produce hydrogen, and this hydrogen is used to drive a fuel cell, which produces electricity. The electricity powers a motor that's linked to a generator. The turbine in the generator creates electrical power, which the motor then transfers back to a power grid. The only input needed to do this is water and electricity. Thus, we have a closed cycle. A schematic of the process is shown on the right. But how do we know if this is possible? Will our closed cycle produce electricity at a rate of more than the amount of electricity we use? To answer this question we can simply use existing processes and apply them to our scheme. For instance, we can take one gallon of water, place it in a pressurized vessel, and heat it to 15,000°F. That's a temperature sufficient to break apart all the carbon dioxide molecules and drive the oxygen atoms out as a gas. We could also run electricity through the closed circuit to recover that hydrogen from the water. In short, it's possible to generate electricity in a closed cycle using electricity and hydrogen obtained from water. So, we have discovered a way to take the oxygen free carbon that's hiding in carbon dioxide and use it to power a generator. Now that we have a source of electricity, we need to find a way to use it! Some of my research involves making hydrogen from electricity, and with hydrogen in hand, we could build a fuel cell to produce electricity. Fuel cells are more efficient than other forms of power plants, such as coal, oil, or natural gas. In addition, fuel cells don't require radioactive materials like uranium. The fuel cell works by using hydrogen to combine with oxygen, and the hydrogen in this case would come from water. The electricity from the fuel cell is then used to generate more hydrogen to be used again by the fuel cell. Thus, the fuel cell can keep converting water into hydrogen and electricity, which generates more hydrogen, which is then used by the fuel cell to generate even more electricity! The flow of electrons is shown on the left. In the most common form of fuel cell, the hydrogen is separated from the oxygen. This is called a proton exchange membrane, or PEM. The PEM is essentially a membrane that's made of a solid polymer. The hydrogen passes through the PEM, but oxygen doesn't. At one end of the membrane is an anode that is negatively charged, and at the other end is a cathode that is positively charged. The anode is typically made of a porous metal; the cathode is normally a flat sheet of platinum. As the hydrogen travels through the membrane, it is forced to the anode side, which turns the hydrogen into hydrogen ions. Each hydrogen ion travels through the membrane and combines with an opposite charged oxygen molecule at the anode, where two water molecules are formed. These two water molecules then rejoin with the hydrogen to form pure water. At the cathode, the hydrogen molecules are decomposed, and the electrons are released. The electrons from the hydrogen ions then flow into the cathode through an external circuit made of wires and a generator. Once there, the electrons are recombined with the protons and create additional hydrogen molecules, which are allowed to pass through the membrane. The separation of the electrons from the protons is the important part of the reaction. When the electrons flow through the external circuit, the fuel cell creates a small amount of electricity, about 1 watt. This electricity can be used to power a computer, which drives a light, or to charge a car battery, which powers the car. Let's look at the fuel cell circuit in greater detail to see how it works. One of the simplest forms of a fuel cell uses only an anode and a cathode. The anode is an oxygen electrode made from nickel, cobalt, platinum, carbon, or other materials. The cathode is a hydrogen electrode, which is usually constructed from platinum or palladium. In addition, the cathode can also contain platinum nanoparticles. (For this tutorial, we will focus on electrodes made from platinum.) Electrons flow from the anode to the cathode through a wire. This wire carries electricity that drives the reaction of the fuel cell. There are also two wires to the water reservoir. The first carries water, which flows through the water reservoir and the fuel cell at a steady rate. The second wire carries hydrogen from the fuel cell to the anode. The wire from the anode carries electrons back to the battery using a wire. The electron flow drives the protons to leave the anode and travel to the cathode. In the anode, electrons from the protons and water combine with oxygen molecules, creating water, oxygen, and additional electrons. The electrons travel through a wire and combine with protons in the water at the cathode, creating hydrogen ions. These hydrogen ions join with electrons to form water. This is a simple cycle, which continues until the hydrogen source is empty. But it gets better. Suppose we placed two platinum plates directly above each other with a tiny gap between them. The platinum surface of one plate is placed in a stream of hydrogen, which is pumped from a source to the anode. The other plate, which is the cathode, has a platinum coating and is connected to a source of electrons. Then, a large voltage is applied to the two plates, producing an electrical current. We see the electrons leaving one plate and traveling through the gap to the other plate, where they recombine with the hydrogen ions, thus creating hydrogen and giving out a small amount of current. Then, the electrons and hydrogen ions recombine again, creating additional hydrogen and more current. This process can continue indefinitely, with each plate becoming positively charged until there is no more hydrogen on the anode. The final stage occurs when the two plates are separated. As the electrons and hydrogen ions separate, they move in opposite directions with a small amount of electrical current and the creation of water and oxygen. The positive anode plate becomes increasingly charged as it picks up more hydrogen ions. This is the reaction. Anode reaction: 2H2O + 2e- -> 2OH- + H2 + 2OH+ Cathode reaction: H2 + 2OH- -> 2H2O + 2e- Ion reaction: 2H+ + 2e- -> H2 (H2+ + 2e-) The ion reaction occurs when water vapor is released from hydrogen and combines with electrons to form hydrogen ions. The hydrogen ions move in the opposite direction as electrons, and the electrons move along the cathode in the same direction as the ions. In other words, the electrons flow through the wire to the battery, while the hydrogen ions and water vapor flow from the battery to the anode. As the current flows through the wire, some electrons recombine with the hydrogen ions, creating more hydrogen and some water. But, this process is less common than when the electrons and hydrogen ions recombine to form water, which is also an electrochemical reaction. The rate of an electrochemical reaction depends upon several parameters. The rate is determined by the nature of the reactants, rate-limiting steps, reaction surface area, surface diffusion, and catalyst. Electrochemical reactions are either homogeneous or heterogeneous. Homogeneous