How Hydrogen Cars Work
Hydrogen Cars and how they Work
How Hydrogen Cars Work
The car of the future is here today. Of course, you can't buy one yet; but if you live in California you can lease one. It doesn't use gasoline and it doesn't pollute the air. In fact, it produces steam instead of exhaust. So what's the mystery fuel? Hydrogen -- the simplest and most abundant element in the universe. And some people think that in 20 to 30 years, we'll all be driving these hydrogen-powered, fuel-efficient vehicles.
Although hydrogen-powered cars have a science fiction quality to them, the idea isn't really new. Actually, the technology for using hydrogen to generate power has been around since the first part of the 19th century -- that's longer than cars have been around. What's new is that you might actually see a hydrogen-powered car on the road, with steam coming out of its exhaust pipe instead of foul-smelling gases. Several hydrogen cars are now in existence, but most of them are concept cars. These eco-friendly driving machines include the Chevrolet Equinox, the BMW 745h and the one that's currently available for lease in California, the Honda FCX.
What makes a hydrogen car possible is a device called a fuel cell, which converts hydrogen to electricity, giving off only heat and water as byproducts. Because it's non-polluting, hydrogen seems like the ideal fuel for the 21st century. A lot of people in the government and the auto industry are excited about its potential. Hydrogen cars have the potential to be fuel-efficient and offer the hope of eco-friendly, green driving. But there are still a lot of problems that need to be overcome and questions that need to be answered before hydrogen becomes the fuel of choice for enough people to make much difference in our current use of fossil fuels. For instance, where will we get the hydrogen? How expensive will these fuel-efficient cars be to purchase? Will you be able to find a hydrogen fuelling station to refill your tank? And, perhaps most importantly, as a fuel, is hydrogen really as non-polluting as it seems?
We'll look at those questions in the pages that follow, but we can give you one quick answer right now: Unless you happen to live in very specific parts of the country and have pockets lined with cash, don't expect a hydrogen car in your driveway within the next decade.
Hydrogen Fuel Cells
A hydrogen fuel cell powered bus leaves the Connecticut Convention Center in Hartford, Conn., for a demonstration ride.
In 1839, the Welsh scientist Sir William Robert Grove took the familiar electrochemical process of electrolysis, which uses electricity to produce hydrogen from water, and reversed it, generating electricity and water from hydrogen. He called his invention a gas voltaic battery, but today we know it as a hydrogen fuel cell. Much later, in the middle of the 20th century, the technology was further developed by the inventor Francis Bacon. The technology that these two inventors devised is essential to the operation of a hydrogen car.
The first practical fuel cell system was developed in the early 1960s by General Electric for use in orbital space capsules. And then, in the 1990s fuel cells began appearing in city buses. so we know that powering vehicles with fuel cells is feasible. You can think of a fuel cell as a kind of battery, except that while a battery keeps its fuel inside itself, a fuel cell needs to be refilled. The fuel for a hydrogen fuel cell is, as the name suggests, hydrogen. As you might recall from high school chemistry class, hydrogen is the simplest of all elements. An atom of hydrogen consists of a single electron and a single proton. The fuel cell generates electricity by stripping the electrons from the protons and using the electrons to create a pure stream of electricity. The ionized hydrogen atoms then combine with oxygen to form water. The other byproduct of this process is heat, so this water generally takes the form of steam. How's that for eco-friendly driving?
The type of fuel cell used in cars is the polymer exchange membrane (or PEM) fuel cell. PEM fuel cells have the advantage of being light and small. They consist of two electrodes (a negatively charged anode and a positively charged cathode), a catalyst and a membrane. Hydrogen is forced into the fuel cell at the anode in the form of H2 molecules, each of which contains two hydrogen atoms. A catalyst at the anode breaks the molecules into hydrogen ions (the protons) and a flow of electricity (the electrons). The ions pass through the membrane, but the electricity has to go around. While it's doing so, it can be harnessed to do work. Just as hydrogen is forced into the fuel cell at the anode, oxygen is forced in at the cathode. The protons and electrons reunite at the cathode and join with the oxygen to form water, most of which become the fuel cell's exhaust. Fuel cells are designed to be flat and thin, mainly so they can be stacked. The more fuel cells in the stack, the greater the voltage of the electricity that the stack produces.
Many people think that fuel-efficient vehicles like hydrogen-powered cars will be crucial in meeting the energy demands of the 21st century. In 2003, President George W. Bush announced a $1.2 billion Freedom Fuel Initiative in support of the development of fuel cell technology. Fuel cells have two major advantages over fossil fuels. First, they don't deplete the world's finite supply of oil, which helps us preserve the existing supplies and they could also reduce our dependency on foreign oil. Second, the only byproduct from a fuel cell's operation is heat and water, which means fuel cells don't produce pollution. This is vitally important in a time when carbon emissions from cars are believed to be promoting global warming.
On the next page we'll look at how hydrogen cars and fuel cells are produced. And perhaps more importantly we'll look at where the hydrogen itself will come from.
Hydrogen Car Production
The Earth has plenty of hydrogen available in the form of water; however, separating it, collecting it and storing it may prove to be quite difficult.
So how do manufacturers actually build fuel-efficient vehicles, like fuel cell cars? Well, hydrogen car production is not vastly different from producing typical cars. Of course, the drive train, for instance, and the electrical systems will be somewhat unique because a fuel cell creates electricity. Therefore, a hydrogen-powered car and electric car have a lot in common in that respect. Perhaps a more important question is how the hydrogen itself will be produced. Given that hydrogen is the most abundant element in the universe, constituting roughly 90 percent of the atoms in existence, you'd think that this wouldn't be a problem. Well, think again. Hydrogen is also the lightest element in the universe and any uncontained hydrogen on the surface of the Earth will immediately float off into outer space. What hydrogen remains on this planet is bound with other elements in molecular form, most commonly in water (H2O) molecules. And there happens to be a lot of H2O on the surface of the Earth.
But how do we separate the hydrogen molecules in the water from the oxygen molecules? And if we don't use water as a hydrogen source, where else can we get hydrogen?
The simplest way of getting hydrogen from water is the one that Sir William Grove knew about more than 150 years ago: electrolysis. If you pass an electric current through water, the H2O molecules break down. Similar to fuel cell operation, this process uses an anode and a cathode, usually made from inert metals. When an electric current is applied to the water, hydrogen forms at the cathode, and oxygen forms at the anode. Although this process is slow, it can be done on a large scale.
An alternative source for hydrogen is natural gas, which consists of naturally occurring hydrocarbons. A process called steam reformation can be used to separate the hydrogen in the gas from the carbon. At present, this is the most common method of industrial-scale production of hydrogen and would likely be the first method used to produce the hydrogen for fuel-cell vehicles. Unfortunately, this process uses fossil fuels -- the natural gas -- so if the point of building cars that run on hydrogen is to avoid depleting fossil fuel reserves, natural gas would be the worst possible source of this fuel.
Some experts have suggested that it might be possible to build miniature hydrogen plants that will fit in the average person's garage, so it won't even be necessary to drive to the local fueling station to fill up the car's hydrogen tank. The most extreme form of this idea has been the suggestion that electrolysis could be performed inside the car itself, which would make possible the astounding idea of a car that runs on water! However, the power for the electrolysis has to come from some sort of battery, so a water-powered car would need to be periodically recharged.
So, are green driving machines like fuel-cell equipped vehicles really the cars of the future? Many people hope so, but there are several potential roadblocks on the way to a world where people get around in cars that run on hydrogen.
What is a Hydrogen Fuel Cell?
Although hydrogen is in its infancy as a fuel source, its future is incredibly bright. The technology behind hydrogen fuel cells is improving daily and its viability as a replacement to the internal combustion engine seems likely. Hydrogen is already being used in specialty vehicles such as forklifts and buses, and it’s only a matter of time before infrastructure is in place to serve the consumer automotive market. Why do hydrogen fuel cells have such great appeal? Because their only byproducts are heat and water vapor, making hydrogen fuel cells a truly zero-emission locomotive technology.
What is a Fuel Cell?
A fuel cell is a device that generates electrical power through a chemical reaction by converting a fuel (hydrogen) into electricity. Although fuel cells and batteries are both considered electrochemical cells and consist of similar structure, fuel cells require a continuous source of fuel and oxygen to run; similar to how an internal combustion engine needs a continuous flow of gasoline or diesel.
How Does it Work?
A fuel cell needs three main components to create the chemical reaction: an anode, cathode and an electrolyte. First, a hydrogen fuel is channeled to the anode via flow fields. Hydrogen atoms become ionized (stripped of electrons), and now carry only a positive charge. Then, oxygen enters the fuel cell at the cathode, where it combines with electrons returning from the electrical circuit and the ionized hydrogen atoms. Next, after the oxygen atom picks up the electrons, it then travels through the electrolyte to combine with the hydrogen ion. The combination of oxygen and ionized hydrogen serve as the basis for the chemical reaction.
A polymer electrolyte membrane permits the appropriate ions to pass between the anode and the cathode. If the electrolyte gave free control for all electrons or ions to pass freely, it would disrupt the chemical reaction. At the end of the process the positively charged hydrogen atoms react with the oxygen to form both water and heat while creating an electrical charge.
Within the fuel market there are many different applications with different power requirements. In order to provide adequate power, individual fuel cells can be assembled together forming a stack. A fuel cell stack can be sized for just the right amount of energy for the application.
Where are fuel cells used?
Fuel Cells are used in both stationary and motive power applications for:
- Cars, trucks, buses, and recreational vehicles
- Material handling equipment
- Act as a primary power source for high-volume data centers or commercial, industrial, and residential buildings
- Backup power source to critical computer and communications networks
- Generating power on-site
It’s called a hydrogen fuel-cell vehicle, but unless you live in California, you may have never seen one on the road.
These days, electric cars driven by batteries seem destined to rule our roads, while hydrogen cars—once toasted as the vehicle of the future—are rare and relatively unheralded. Fuel cells actually have lots of advantages over the competition, including better miles per gallon and faster refueling times.
So what happened to the hydrogen cars we were promised?
How Hydrogen Cars Work
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