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Tuesday, 10 August 2010

FUEL CELL

An Introduction to Fuel Cells: Green Energy
Abstract:
A fuel cell is a device that uses hydrogen (or hydrogen-rich fuel) and oxygen to create electricity by an electrochemical process. If pure hydrogen is used as a fuel, fuel cells emit only heat and water as a by-product. Several fuel cell types are under development, and they have a variety of potential applications. Fuel cells are being developed to power passenger vehicles, commercial buildings, homes, and even small devices such as laptop computers.
What Is A Fuel Cell?
In principle, a fuel cell operates like a battery. Unlike a battery, a fuel cell does not run down or require recharging. It will produce energy in the form of electricity and heat as long as fuel is supplied.
A fuel cell consists of two electrodes sandwiched around an electrolyte. Oxygen passes over one electrode and hydrogen over the other, generating electricity, water and heat.
Hydrogen fuel is fed into the "anode" of the fuel cell. Oxygen (or air) enters the fuel cell through the cathode. Encouraged by a catalyst, the hydrogen atom splits into a proton and an electron, which take different paths to the cathode. The proton passes through the electrolyte. The electrons create a separate current that can be utilized before they return to the cathode, to be reunited with the hydrogen and oxygen in a molecule of water.
How Fuel Cells Work?
Fuel Cell Components & Function: A fuel cell is a device that uses hydrogen (or hydrogen-rich fuel) and oxygen to create electricity by an electrochemical process. A single fuel cell consists of an electrolyte sandwiched between two thin electrodes (a porous anode and cathode). While there are different fuel cell types, all work on the same principle: Hydrogen, or a hydrogen-rich fuel, is fed to the anode where a catalyst separates hydrogen's negatively charged electrons from positively charged ions (protons). At the cathode, oxygen combines with electrons and, in some cases, with species such as protons or water, resulting in water or hydroxide ions, respectively. For polymer exchange membrane (PEM) and phosphoric acid fuel cells, protons move through the electrolyte to the cathode to combine with oxygen and electrons, producing water and heat. For alkaline, molten carbonate, and solid oxide fuel cells, negative ions travel through the electrolyte to the anode where they combine with hydrogen to generate water and electrons. The electrons from the anode side of the cell cannot pass through the membrane to the positively charged cathode; they must travel around it via an electrical circuit to reach the other side of the cell. This movement of electrons is an electrical current. The amount of power produced by a fuel cell depends upon several factors, such as fuel cell type, cell size, the temperature at which it operates, and the pressure at which the gases are supplied to the cell. Still, a single fuel cell produces enough electricity for only the smallest applications. Therefore, individual fuel cells are typically combined in series into a fuel cell stack. A typical fuel cell stack may consist of hundreds of fuel cells. Direct hydrogen fuel cells produce pure water as the only emission. This water is typically released as water vapour. Fuel cells release less water vapour than internal combustion engines producing the same amount of power.
Pure Hydrogen: Most fuel cell systems are fueled with pure hydrogen gas, which is stored onboard as a compressed gas. Since hydrogen gas has a low energy density, it is difficult to store enough hydrogen to generate the same amount of power as with conventional fuels such as gasoline. This is a significant problem for fuel cell vehicles, which need to have a driving range of 300-400 miles between refueling to be competitive gasoline vehicles. High-pressure tanks and other technologies are being developed to allow larger amounts of hydrogen to be stored in tanks small enough for passenger cars and trucks. In addition to onboard storage problems, our current infrastructure for getting liquid fuel to consumers can't be used for gaseous hydrogen. New facilities and delivery systems must be built, which will require significant time and resources. Costs for large-scale deployment will be substantial.
Hydrogen-rich Fuels: Fuel cell systems can also be fueled with hydrogen-rich fuels, such as methanol, natural gas, gasoline, or gasified coal. In many fuel cell systems, these fuels are passed through onboard "reformers" that extract hydrogen from the fuel. Onboard reforming has several advantages:There are also several disadvantages to reforming hydrogen-rich fuels: Onboard reformers add to the complexity, cost, and maintenance demands of fuel cell systems.High-temperature fuel cell systems can reform fuels within the fuel cell itself-a process called internal reforming-removing the need for onboard reformers and their associated costs. Internal reforming, however, does emit carbon dioxide, just like onboard reforming. In addition, impurities in the gaseous fuel can reduce cell efficiency.
Fuel Cell Systems . Most fuel cell systems consist of four basic components:
Fuel processor : The fuel processor converts fuel into a form useable by the fuel cell. If hydrogen is fed to the system, a processor may not be required or it may only be needed to filter impurities out of the hydrogen gas. If the system is powered by a hydrogen-rich conventional fuel such as methanol, gasoline, diesel, or gasified coal, a reformer is typically used to convert hydrocarbons into a gas mixture of hydrogen and carbon compounds called "reformate." In many cases, the reformate is then sent to another reactor to remove impurities, such as carbon oxides or sulfur, before it is sent to the fuel cell stack. This prevents impurities in the gas from binding with the fuel cell catalysts. This binding process is also called "poisoning" since it reduces the efficiency and life expectancy of the fuel cell. Some fuel cells, such as molten carbonate and solid oxide fuel cells, operate at temperatures high enough that the fuel can be reformed in the fuel cell itself. This is called internal reforming. Fuel cells that use internal reforming still need traps to remove impurities from the unreformed fuel before it reaches the fuel cell. Both internal and external reforming release carbon dioxide, but less than the amount emitted by internal combustion engines, such as those used in gasoline-powered vehicles. Energy Conversion Device - The Fuel Cell Stack :The fuel cell stack is the energy conversion device. It generates electricity in the form of direct current (DC) from chemical reactions that take place in the fuel cell. The fuel cell and fuel cell stack are covered under Fuel Cell Components and Function.
Current Inverters &Conditioners: The purpose of current inverters and conditioners is to adapt the electrical current from the fuel cell to suit the electrical needs of the application, whether it is a simple electrical motor or a complex utility power grid. Fuel cells produce electricity in the form of direct current (DC). If the fuel cell is used to power equipment using AC, the direct current will have to be converted to alternating current. Both AC and DC power must be conditioned. Power conditioning includes controlling current flow (amperes), voltage, frequency, and other characteristics of the electrical current to meet the needs of the application. Conversion and conditioning reduce system efficiency only slightly, around 2 to 6 percent.
Heat Recovery System: Fuel cell systems are not primarily used to generate heat. However, since significant amounts of heat are generated by some fuel cell systems-especially those that operate at high temperatures such as solid oxide and molten carbonate systems-this excess energy can be used to produce steam or hot water or converted to electricity via a gas turbine or other technology. This increases the overall energy efficiency of the systems.
Types of Fuel Cells

Fuel cells are classified primarily by the kind of electrolyte they employ. This determines the kind of chemical reactions that take place in the cell, the kind of catalysts required, the temperature range in which the cell operates, the fuel required, and other factors. These characteristics, in turn, affect the applications for which these cells are most suitable. There are several types of fuel cells currently under development, each with its own advantages, limitations, and potential applications. A few of the most promising types include Polymer Electrolyte Membrane (PEM) Phosphoric Acid Direct Methanol Alkaline Molten Carbonate Solid Oxide Regenerative (Reversible)

Polymer Electrolyte Membrane
Polymer electrolyte membrane (PEM) fuel cells-also called proton exchange membrane fuel cells-deliver high power density and offer the advantages of low weight and volume, compared to other fuel cells. PEM fuel cells use a solid polymer as an electrolyte and porous carbon electrodes containing a platinum catalyst. They need only hydrogen, oxygen from the air, and water to operate and do not require corrosive fluids like some fuel cells.
They are typically fueled with pure hydrogen supplied from storage tanks or onboard reformers. Polymer electrolyte membrane fuel cells operate at relatively low temperatures, around 80°C (176°F). Low temperature operation allows them to start quickly (less warm-up time) and results in less wear on system components, resulting in better durability. However, it requires that a noble-metal catalyst (typically platinum) be used to separate the hydrogen's electrons and protons, adding to system cost. The platinum catalyst is also extremely sensitive to CO poisoning, making it necessary to employ an additional reactor to reduce CO in the fuel gas if the hydrogen is derived from an alcohol or hydrocarbon fuel. This also adds cost. Developers are currently exploring platinum/ruthenium catalysts that are more resistant to CO. PEM fuel cells are used primarily for transportation applications and some stationary applications. Due to their fast startup time, low sensitivity to orientation, and favorable power-to-weight ratio, PEM fuel cells are particularly suitable for use in passenger vehicles, such as cars and buses. A significant barrier to using these fuel cells in vehicles is hydrogen storage. Most fuel cell vehicles (FCVs) powered by pure hydrogen must store the hydrogen onboard as a compressed gas in pressurized tanks. Due to the low energy density of hydrogen, it is difficult to store enough hydrogen onboard to allow vehicles to travel the same distance as gasoline-powered vehicles before refueling, typically 300-400 miles. Higher-density liquid fuels such as methanol, ethanol, natural gas, liquefied petroleum gas, and gasoline can be used for fuel, but the vehicles must have an onboard fuel processor to reform the methanol to hydrogen. This increases costs and maintenance requirements. The reformer also releases carbon dioxide (a greenhouse gas), though less than that emitted from current gasoline-powered engines.
Phosphoric Acid

Phosphoric acid fuel cells use liquid phosphoric acid as an electrolyte-the acid is contained in a Teflon-bonded silicon carbide matrix-and porous carbon electrodes containing a platinum catalyst. The chemical reactions that take place in the cell are shown in the diagram .The phosphoric acid fuel cell (PAFC) is considered the "first generation" of modern fuel cells. It is one of the most mature cell types and the first to be used commercially, with over 200 units currently in use
. This type of fuel cell is typically used for stationary power generation, but some PAFCs have been used to power large vehicles such as city buses. PAFCs are more tolerant of impurities in the reformate than PEM cells, which are easily "poisoned" by carbon monoxide-carbon monoxide binds to the platinum catalyst at the anode, decreasing the fuel cell's efficiency. They are 85 percent efficient when used for the co-generation of electricity and heat, but less efficient at generating electricity alone (37 to 42 percent). This is only slightly more efficient than combustion-based power plants, which typically operate at 33 to 35 percent efficiency. PAFCs are also less powerful than other fuel cells, given the same weight and volume. As a result, these fuel cells are typically large and heavy. PAFCs are also expensive. Like PEM fuel cells, PAFCs require an expensive platinum catalyst, which raises the cost of the fuel cell. A typical phosphoric acid fuel cell costs between $4,000 and $4,500 per kilowatt to operate.
Direct Methanol
Most fuel cells are powered by hydrogen, which can be fed to the fuel cell system directly or can be generated within the fuel cell system by reforming hydrogen-rich fuels such as methanol, ethanol, and hydrocarbon fuels. Direct methanol fuel cells (DMFCs), however, are powered by pure methanol, which is mixed with steam and fed directly to the fuel cell anode. Direct methanol fuel cells do not have many of the fuel storage problems typical of some fuel cells since methanol has a higher energy density than hydrogen-though less than gasoline or diesel fuel. Methanol is also easier to transport and supply to the public using our current infrastructure since it is a liquid, like gasoline. Direct methanol fuel cell technology is relatively new compared to that of fuel cells powered by pure hydrogen.
Alkaline
Alkaline fuel cells (AFCs) were one of the first fuel cell technologies developed, and they were the first type widely used in the U.S. space program to produce electrical energy and water onboard spacecraft. These fuel cells use a solution of potassium hydroxide in water as the electrolyte and can use a variety of non-precious metals as a catalyst at the anode and cathode.
. High-temperature AFCs operate at temperatures between 100ºC and 250ºC (212ºF and 482ºF). However, more-recent AFC designs operate at lower temperatures of roughly 23ºC to 70ºC (74ºF to 158ºF). AFCs are high-performance fuel cells due to the rate at which chemical reactions take place in the cell. They are also very efficient, reaching efficiencies of 60 percent in space applications. The disadvantage of this fuel cell type is that it is easily poisoned by carbon dioxide (CO2). In fact, even the small amount of CO2 in the air can affect the cell's operation, making it necessary to purify both the hydrogen and oxygen used in the cell. This purification process is costly. Susceptibility to poisoning also affects the cell's lifetime (the amount of time before it must be replaced), further adding to cost. Cost is less of a factor for remote locations such as space or under the sea. However, to effectively compete in most mainstream commercial markets, these fuel cells will have to become more cost effective. AFC stacks have been shown to maintain sufficiently stable operation for more than 8,000 operating hours. To be economically viable in large-scale utility applications, these fuel cells need to reach operating times exceeding 40,000 hours. This is possibly the most significant obstacle in commercializing this fuel cell technology.
Molten Carbonate
Molten carbonate fuel cells (MCFCs) are currently being developed for natural gas and coal-based power plants for electrical utility, industrial, and military applications. MCFCs are high-temperature fuel cells that use an electrolyte composed of a molten carbonate salt mixture suspended in a porous, chemically inert ceramic lithium aluminum oxide (LiAlO2) matrix. Since they operate at extremely high temperatures of 650ºC (roughly 1,200ºF) and above, non-precious metals can be used as catalysts at the anode and cathode, reducing costs. Improved efficiency is another reason MCFCs offer significant cost reductions over phosphoric acid fuel cells (PAFCs). Molten carbonate fuel cells can reach efficiencies approaching 60 percent, considerably higher than the 37-42 percent efficiencies of a phosphoric acid fuel cell plant.
. When the waste heat is captured and used, overall fuel efficiencies can be as high as 85 percent. Unlike alkaline, phosphoric acid, and polymer electrolyte membrane fuel cells, MCFCs don't require an external reformer to convert more energy-dense fuels to hydrogen. Due to the high temperatures at which they operate, these fuels are converted to hydrogen within the fuel cell itself by a process called internal reforming, which also reduces cost. Molten carbonate fuel cells are not prone to carbon monoxide or carbon dioxide "poisoning"-they can even use carbon oxides as fuel-making them more attractive for fueling with gases made from coal. Although they are more resistant to impurities than other fuel cell types, scientists are looking for ways to make MCFCs resistant enough to impurities from coal, such as sulfur and particulates. The primary disadvantage of current MCFC technology is durability. The high temperatures at which these cells operate and the corrosive electrolyte used accelerate component breakdown and corrosion, decreasing cell life. Scientists are currently exploring corrosion-resistant materials for components as well as fuel cell designs that increase cell life without decreasing performance.
Solid Oxide
Solid oxide fuel cells (SOFCs) use a hard, non-porous ceramic compound as the electrolyte. Since the electrolyte is a solid, the cells do not have to be constructed in the plate-like configuration typical of other fuel cell types. SOFCs are expected to be around 50-60 percent efficient at converting fuel to electricity. In applications designed to capture and utilize the system's waste heat (co-generation), overall fuel use efficiencies could top 80-85 percent. Solid oxide fuel cells operate at very high temperatures-around 1,000ºC (1,830ºF). High temperature operation removes the need for precious-metal catalyst, thereby reducing cost. It also allows SOFCs to reform fuels internally, which enables the use of a variety of fuels and reduces the cost associated with adding a reformer to the system.

SOFCs are also the most sulfur-resistant fuel cell type; they can tolerate several orders of magnitude more sulfur than other cell types. In addition, they are not poisoned by carbon monoxide (CO), which can even be used as fuel. This allows SOFCs to use gases made from coal. High-temperature operation has disadvantages. It results in a slow startup and requires significant thermal shielding to retain heat and protect personnel, which may be acceptable for utility applications but not for transportation and small portable applications. The high operating temperatures also place stringent durability requirements on materials. The development of low-cost materials with high durability at cell operating temperatures is the key technical challenge facing this technology. Scientists are currently exploring the potential for developing lower-temperature SOFCs operating at or below 800ºC that have fewer durability problems and cost less. Lower-temperature SOFCs produce less electrical power, however, and stack materials that will function in this lower temperature range have not been identified.
Regenerative (Reversible) Fuel Cells :: Regenerative fuel cells produce electricity from hydrogen and oxygen and generate heat and water as byproducts, just like other fuel cells. However, regenerative fuel cell systems can also use electricity from solar power or some other source to divide the excess water into oxygen and hydrogen fuel.
BENEFITS OF FUEL CELLS

New Markets. The current market for fuel cells is about $218 million and will rise to $2.4 billion by 2004, reaching $7 billion by 2009, according to studies by the Business Communications Company.
The studies estimate the 2004 markets for fuel cells to break down as follows:
• $850 million - electric power generation
• $750 million - motor vehicles
• $200 million - portable electronic equipment
• $200 million - military/aerospace
• $400 million - other
Energy Security. Passenger vehicles alone consume 6 million barrels of oil every single day, equivalent to 85 percent of oil imports.
• If just 20 percent of cars used fuel cells, we could cut oil imports by 1.5 million barrels every day.
• If every new vehicle bought next year was equipped with a 60-kW fuel cell, we would double the amount of the country's available electricity supply.
• 10,000 fuel cell vehicles running on non-petroleum fuel would reduce oil consumption by 6.98 million gallons per year.
One study forecasts that there will be millions of fuel cell vehicles on the road by 2010.* Fuel cell power will reach tens of thousands of vehicles by 2003 to 2004.
• ABI estimates that, by 2010, automotive fuel cells will have a nearly 4 percent market share - 608,000 vehicles.
• Market penetration in 2010 could rise as high as 1.2 million vehicles, representing 7.6 percent of the total U.S. new car market.
Clean and Efficient. Fuel cells could dramatically reduce urban air pollution, decrease oil imports, reduce the trade deficit and produce American jobs.
On the stationary side, fuel cells are ideal for power generation, either connected to the electric grid to provide supplemental power and backup assurance for critical areas, or installed as a grid-independent generator for on-site service in areas that are inaccessible by power lines. Since fuel cells operate silently, they reduce noise pollution as well as air pollution and the waste heat from a fuel cell can be used to provide hot water or space heating. They are highly efficient and low maintenance.
Fuel Cell Emissions. Fuel cells running on hydrogen derived from a renewable source will emit nothing but water vapor.
Why Are Hydrogen & Fuel Cells Important?
Widespread use of hydrogen as an energy source in this country could help address concerns about energy security, global climate change, and air quality. Fuel cells are an important enabling technology for the Hydrogen Future and have the potential to revolutionize the way we power our nation, offering cleaner, more-efficient alternatives to the combustion of gasoline and other fossil fuels. These benefits are explained in more detail below.
Strengthen National Energy Security : Hydrogen and fuel cell technology have the potential to strengthen our national energy security by reducing our dependence on foreign oil. The U.S. uses about 20 million barrels of oil per day, at a cost of about $2 billion a week. Much of this is used to power highway vehicles. In fact, half of the oil used to produce the gasoline you put in your tank is imported. Hydrogen can be derived from a variety of domestically available primary sources, including fossil fuels, renewables, and nuclear power. This flexibility would make us less dependent upon oil from foreign countries.
Reduce Greenhouse Gas Emissions :Greenhouse gases are thought to be responsible for changes in global climate. They trap excess heat from the sun's infrared radiation that would otherwise escape into space, much like a greenhouse is used to trap heat. When we drive our cars, and light, heat, and cool our homes, we generate greenhouse gases. But if we used hydrogen in very high efficiency fuel cells for our transportation and to generate power, we could significantly reduce the GHG emissions - especially if the hydrogen is produced using renewable resources, nuclear power, or clean fossil technologies.
Reduce Air Pollution : The combustion of fossil fuels by electric power plants, vehicles, and other sources is responsible for most of the smog and harmful particulates in the air. Fuel cells powered by pure hydrogen emit no harmful pollutants. Fuel cells that use a reformer to convert fuels such as natural gas, methanol, or gasoline to hydrogen do emit small amounts of air pollutants such as carbon monoxide (CO), although it is much less than the amount produced by the combustion of fossil fuels.
Improve Energy Efficiency :Fuel cells are significantly more energy efficient than combustion-based power generation technologies. A conventional combustion-based power plant typically generates electricity at efficiencies of 33 to 35 percent, while fuel cell plants can generate electricity at efficiencies of up to 60 percent. When fuel cells are used to generate electricity and heat (co-generation), they can reach efficiencies of up to 85 percent. Internal-combustion engines in today's automobiles convert less than 30 percent of the energy in gasoline into power that moves the vehicle. Vehicles using electric motors powered by hydrogen fuel cells are much more energy efficient, utilizing 40-60 percent of the fuel's energy. Even FCVs that reform hydrogen from gasoline can use about 40 percent of the energy in the fuel.
Applications for Fuel Cells
1.Stationary
2.Residential
3.Transportation
4.Portable Power
There are many uses for fuel cells - right now, all of the major automakers are working to commercialize a fuel cell car. Fuel cells are powering buses, boats, trains, planes, scooters, even bicycles. There are fuel cell-powered vending machines, vacuum cleaners and highway road signs. Miniature fuel cells for cellular phones, laptop computers and portable electronics are on their way to market. Hospitals, credit card centers, police stations, and banks are all using fuel cells to provide power to their facilities. Wastewater treatment plants and landfills are using fuel cells to convert the methane gas they produce into electricity. The possibilities are endless.
Stationary. More than 200 fuel cell systems have been installed all over the world - in hospitals, nursing homes, hotels, office buildings, schools, utility power plants, and an airport terminal, providing primary power or backup. In large-scale building systems, fuel cells can reduce facility energy service costs by 20% to 40% over conventional energy service.
Residential. Fuel cells are ideal for power generation, either connected to the electric grid to provide supplemental power and backup assurance for critical areas, or installed as a grid-independent generator for on-site service in areas that are inaccessible by power lines. Since fuel cells operate silently, they reduce noise pollution as well as air pollution and the waste heat from a fuel cell can be used to provide hot water or space heating for a home. Many of the prototypes being tested and demonstrated for residential use extract hydrogen from propane or natural gas. Transportation. All the major automotive manufacturers have a fuel cell vehicle either in development or in testing right now - Honda, Toyota, DaimlerChrysler, GM, Ford, Hyundai, Volkswagen - you name it. They speculate that the fuel cell vehicle will not be commercialized until at least 2004. For more information on fuel cells in transportation, check out our
Portable Power. Miniature fuel cells, once available to the commercial market, will help consumers talk for up to a month on a cellular phone without recharging. Fuel cells will change the telecommuting world, powering laptops and palm pilots hours longer than batteries. Other applications for micro fuel cells include pagers, video recorders, portable power tools, and low power remote devices such as hearing aids, smoke detectors, burglar alarms, hotel locks and meter readers. These miniature fuel cells generally run on methanol, an inexpensive wood alcohol also used in windshield wiper fluid.
Fuel cells can be used to power a variety of portable devices, from handheld electronics such as cell phones and radios to larger equipment such as portable generators. Other potential applications include laptop computers, personal digital assistants (PDAs), and handheld video cameras-almost any application that has traditionally used batteries. These fuel cells have the potential to last more than three times as long as batteries between refueling. In addition to these smaller applications, fuel cells can be used in portable generators, such as those used to provide electricity for portable equipment. It is estimated that about 1,700 portable fuel cell systems have been developed and operated worldwide, ranging from 1 watt to 1.5 kilowatts in power. The two primary technologies for portable applications are polymer electrolyte membrane (PEM) and direct methanol fuel cell (DMFC) designs. Most portable, fuel-cell-powered products are still in the development and demonstration stages. However, a handful of devices, such as portable power generators, are available commercially on a very limited basis.
Stationary Power
Potential Applications Stationary power is the most mature application for fuel cells. Stationary fuel cell units are used for backup power, power for remote locations, stand-alone power plants for towns and cities, distributed generation for buildings, and co-generation (in which excess thermal energy from electricity generation is used for heat). Approximately, 600 systems that produce 10 kilowatts or more have been built and operated worldwide to date, most fueled by natural gas. Phosphoric acid fuel cells (PAFCs) have typically been used for large-scale applications, but molten carbonate and solid oxide designs have begun to compete with PAFCs and may be commercialized in a few years. It is estimated that more than a thousand smaller stationary fuel cells (less than 10 kilowatts) have been built and operated to power homes and provide backup power. Polymer electrolyte membrane (PEM) fuel cells fueled with natural gas or hydrogen are the primary design used for these smaller systems.
Current Applications :Stationary fuel cell generators for residential use are not yet on the market. Although many stationary fuel cells are being researched, developed, and demonstrated around the world, currently only one system is commercially available in the United States-a 200-kilowatt (PAFC) system produced by UTC Fuel Cells. . .
Transport
Potential Applications Fuel cells can be used to provide propulsion or auxiliary power for many transportation applications. Aside from spacecraft, which typically use alkaline fuel cells for onboard power, polymer electrolyte membrane (PEM) fuel cells are the primary type used in transportation. Highway vehicles. Since highway vehicles account for a large share of petroleum use, carbon dioxide (a primary greenhouse gas) emissions, and air pollution, advances in fuel cell power systems for vehicles could substantially improve our energy security and air quality. While fuel-cell-powered cars are not yet available commercially, almost every major auto manufacturer has a fuel-cell vehicle program, with various targets for demonstration between 2003 and 2006. Other highway-based applications include large passenger buses and long-haul trucks. Fuel cell auxiliary power units (APUs) for commercial trucks could also reduce energy use and emissions, since these vehicles must often run while idle to provide electricity for refrigeration, heaters and air conditioners, and sleeper compartment accessories. Other surface transportation. Other potential surface transportation applications include rail locomotives, mining locomotives, scooters, and personal mobility vehicles for the disabled. Aerospace. Fuel cells are often used in aerospace applications. They have been used to provide auxiliary power in spacecraft since the 1960s all 18 Apollo missions and over 100 Space Shuttle missions. Other similar applications include powering near-Earth orbit (NEO) satellites. Marine vessels.: Ships and submarines are another possible application for fuel cells, providing both propulsion and auxiliary power. Recreational and personal watercraft may also be powered by fuel cells.
Current Applications: Few fuel-cell-powered transportation products are currently in use today; even fewer are available commercially. A handful of fuel-cell-based passenger cars have been leased to government and universities, but they are not yet available for sale to the public.
Conclusion

Fuel cells are being developed to power passenger vehicles, commercial buildings, homes, and even small devices such as laptop computers. Fuel cells have several benefits over conventional combustion-based technologies currently used in many power plants and passenger vehicles. They produce much smaller quantities of greenhouse gases that contribute to global warming and none of the air pollutants that create smog and cause health problems. In fact, if pure hydrogen is used as a fuel, only heat and water are emitted. Fuel cells are more efficient than combustion-based technologies, and the hydrogen used to power them can be obtained from a variety of sources, including fossil fuels, renewable sources, and nuclear energy. Since the fuel can be produced from domestically available resources, fuel cells have the potential to improve national energy security by reducing our dependence on oil from foreign countries. Although the potential benefits of fuel cells are significant, many challenges , technical and otherwise, must be overcome before fuel cells will be a successful, competitive alternative for consumers. These include cost, durability, fuel storage and delivery issues, and public acceptance.

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