Will the Fuel Cell Be Our Future Means of Transportation?
It is reasonable to say that the automobile changed the industrial and social construction of the United States and most of the other countries around the world.
More people are driving more cars than ever before, but the car has contributed to our air and water pollution and forced us to rely on imported oil, helping to create a significant trade imbalance.
Today many people think fuel cell technology will play a pivotal role in a new technological renaissance; just as the internal combustion engine vehicle revolutionized life at the beginning of the 20th century.
British jurist and physicist William R. Grove (1811-1896) made the first fuel cell in 1839. In his experiment he used water and sulfuric acid between two platinum electrodes to electrolytically break down water into hydrogen and oxygen.
Today's innovations in fuel cell technology are addressing local, national, and global environmental needs
The decision to become involved with bringing these innovations into our daily lives is a strategic career opportunity. Fuel cells offer an opportunity for innovation. Helping to make fuel cells become a part of the solution might be a challenge that's too exciting to ignore.
Fuel cells (FC) are electrochemical devices that convert fuel (that is, hydrogen, methanol, methane) directly into electricity at higher efficiency than internal combustion engines and have the potential for higher power storage capacity than lithium-ion batteries.
Fuel cells have the potential to become the dominant technology for automotive engines, power stations, and the power packs for portable electronics.
Technically, a fuel cell is an electrochemical energy conversion device. A fuel cell converts the chemicals hydrogen and oxygen into water, and in the process it produces electricity.
The other electrochemical device that we are all know about is the battery. A battery has all of its chemicals stored inside, and it converts those chemicals into electricity, too. This means that a battery eventually "goes dead" and you either throw it away or recharge it.
With a fuel cell, chemicals constantly flow into the cell so it never goes dead; as long as there is a flow of chemicals into the cell, the electricity flows out of the cell. Most fuel cells in use today use hydrogen and oxygen as the chemicals.
The fuel cell will compete with many other types of energy conversion devices, including the gas turbine power plants of cities, the gasoline engines in cars, and the batteries in laptops.
Combustion engines like the turbine and the gasoline engine burn fuels and use the pressure created by the expansion of the gases to do mechanical work. Batteries convert chemical energy back into electrical energy when needed. Fuel cells are expected to do both tasks more efficiently.
A fuel cell provides a DC (direct current) voltage that can be used to power motors, lights, or any number of electrical appliances.
There are several different types of fuel cells, each using a different chemistry. Fuel cells are usually classified by the type of electrolyte they use.
Some types of fuel cells work well for use in stationary power generation plants. Others may be useful for small portable applications or for powering cars.
The proton exchange membrane fuel cell (PEMFC) is one of the most promising technologies. This is the type of fuel cell that will end up powering cars, buses, and maybe even houses.
Problems with Fuel Cells
As stated before, a fuel cell uses oxygen and hydrogen to produce electricity. The oxygen required for a fuel cell comes from the air.
In fact, in the Polymer Electrolyte Membrane (PEM) fuel cell, ordinary air is pumped into the cathode. Hydrogen is not all that readily available.
Polymer Electrolyte Membrane (PEM) fuel cells are also called "Proton Exchange Membrane fuel cells" and they are the type typically used in automobiles.
Hydrogen has some limitations that make it impractical for use in most applications. For instance, there are no hydrogen pipelines coming into houses, and currently there are no available hydrogen pumps at the local gas stations where people can pull up to re-fill.
Hydrogen is difficult to store and distribute, so it would be much more convenient if fuel cells could use fuels that are more readily available.
This problem is addressed by a device called a reformer. A reformer turns hydrocarbon or alcohol fuels into hydrogen, which is then fed to the fuel cell.
Unfortunately, reformers are not perfect. They generate heat and produce other gases besides hydrogen. They use various devices to try to clean up the hydrogen, but even so, the hydrogen that comes out of them is not pure, and this lowers the efficiency of the fuel cell.
Some of the more promising fuels are natural gas, propane, and methanol. Many people have natural-gas lines or propane tanks at their houses already, so these fuels are the most likely to be used for home fuel cells.
Methanol is a liquid fuel that has similar properties as gasoline. It is just as easy to transport and distribute, so methanol may be a likely candidate to power fuel-cell cars.
Fuel-Cell-Powered Electric Cars
If the fuel cell is powered with pure hydrogen, it has the potential to be up to eighty percent efficient. That is, it converts eighty percent of the energy content of the hydrogen into electrical energy; however, hydrogen is difficult to store in a car.
When a reformer is added to convert methanol to hydrogen, the overall efficiency drops to about thirty to fourty percent.
Gasoline and Battery Power
The efficiency of a gasoline-powered car is surprisingly low. All of the heat that comes out as exhaust or goes into the radiator is wasted energy.
The engine also uses a lot of energy turning the various pumps, fans and generators that keep it going. So the overall efficiency of an automotive gas engine is about twenty percent. That is, only about twenty percent of the thermal-energy content of the gasoline is converted into mechanical work.
Battery-Powered Electric Car
This type of car has a fairly high efficiency. The battery is about ninety percent efficient (most batteries generate some heat, or require heating), and the electric motor/inverter is about eighty percent efficient. This gives an overall efficiency of about seventy-two percent.
That is not the whole story. The electricity used to power the car had to be generated somewhere.
If it was generated at a power plant that used a combustion process (rather than nuclear, hydroelectric, solar, or wind), then only about forty percent of the fuel required by the power plant was converted into electricity.
The process of charging the car requires the conversion of alternating current (AC) power to direct current (DC) power. This process has an efficiency of about ninety percent.
So, a look at the whole cycle, the efficiency of an electric car is seventy-two percent for the car, forty percent for the power plant and ninety percent for charging the car.
That gives an overall efficiency of twenty-six percent. The overall efficiency varies considerably depending on what sort of power plant is used.
If the electricity for the car is generated by a hydroelectric plant; for instance, then it is basically free (no fuel was burned to generate it), and the efficiency of the electric car is about sixty-five percent.
Efficiency is not the only consideration, however. People will not drive a car just because it is the most efficient if it makes them change their behavior. They are concerned about many other issues as well. They want to know:
- Is the car quick and easy to refuel?
- Can it travel a good distance before refueling?
- Is it as fast as the other cars on the road?
- How much pollution does it produce?
This list, of course, goes on and on. In the end, the technology that dominates will be a compromise between efficiency and practicality.
Other Types of Fuel Cells
There are several other types of fuel-cell technologies being developed for possible commercial uses:
- Alkaline fuel cell (AFC): This is one of the oldest designs. It has been used in the U.S. space program since the 1960s.
The AFC is very susceptible to contamination, so it requires pure hydrogen and oxygen. It is also very expensive, so this type of fuel cell is unlikely to be commercialized.
- Phosphoric-acid fuel cell (PAFC): The phosphoric-acid fuel cell has potential for use in small stationary power-generation systems. It operates at a higher temperature than PEM fuel cells, so it has a longer warm-up time. This makes it unsuitable for use in cars.
- Solid oxide fuel cell (SOFC): These fuel cells are best suited for large-scale stationary power generators that could provide electricity for factories or towns.
This type of fuel cell operates at very high temperatures (around 1,832 F, 1,000 C). This high temperature makes reliability a problem, but it also has an advantage: The steam produced by the fuel cell can be channeled into turbines to generate more electricity. This improves the overall efficiency of the system.
- Molten carbonate fuel cell (MCFC): These fuel cells are also best suited for large stationary power generators. They operate at 1,112 F (600 C), so they also generate steam that can be used to generate more power.
They have a lower operating temperature than the SOFC, which means they don't need such exotic materials. This makes the design a little less expensive.
Large Power Generation
Some fuel-cell technologies have the potential to replace conventional combustion power plants. Large fuel cells will be able to generate electricity more efficiently than today's power plants.
The fuel-cell technologies being developed for these power plants will generate electricity directly from hydrogen in the fuel cell, but they will also use the heat and water produced in the cell to power steam turbines and generate even more electricity. There are already large portable fuel-cell systems available for providing backup power to hospitals and factories.
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