- For other uses, see Fuel cell (disambiguation).
A fuel cell is an electrochemical device similar to a battery, but differing from racing fuel cell the latter in that it is designed for continuous replenishment of the reactants consumed; fuel cell for mobile phones i.e. it produces electricity from an external fuel supply of hydrogen and oxygen as opposed to the limited internal energy storage capacity of a battery. Additionally, the electrodes within a battery react and change as a battery is charged or discharged, whereas a fuel cell's electrodes are catalytic and relatively stable.
Typical reactants used in a fuel cell are hydrogen on the anode side and oxygen on the cathode side (a hydrogen cell). In contrast, conventional batteries consume solid reactants and, once these reactants are depleted, must be discarded, recharged with electricity by running the chemical reaction backwards, or, at least in theory, by having their electrodes replaced. Typically in fuel cells, reactants flow in and reaction products flow out, and continuous long-term operation is feasible virtually as long as these flows are maintained.
Fuel fuel cell catalysts cells are often considered to be very attractive in modern applications for their high efficiency and ideally emission-free use, in contrast to currently more common fuels such as pem fuel cell methane or natural gas that generate carbon dioxide. The only by-product of a hydrogen fuel cell is water vapor. There is concern, however, about the energy-consuming process of manufacturing the hydrogen, which may still generate pollution and still requires either fossil fuel, nuclear power generation, or as yet undeveloped alternative generation. In this regard, hydrogen fuel technology itself cannot be said to reduce fossil fuel dependence.
Science
Fuel cells are not constrained by the maximum Carnot cycle efficiency as combustion engines are. Consequently, they can have very high efficiencies in converting chemical energy to electrical energy.
In the archetypal example of a hydrogen/oxygen proton-exchange membrane (or "polymer electrolyte") fuel cell (PEMFC), a proton-conducting polymer membrane separates the anode and cathode sides. Each side has an electrode, typically carbon paper coated with platinum catalyst.
On the anode side, hydrogen diffuses to the anode catalyst where it dissociates into protons and electrons. The protons are conducted through the membrane to the cathode, but the electrons are forced to travel in an external circuit (supplying power) because the membrane is electronically insulating.
On the cathode catalyst, oxygen molecules react with the electrons (which have travelled through the external circuit) and protons to form water.
In this example, the only waste product is water vapor and/or liquid fuel cell construction water.
Fuel cells cannot store energy like a battery, but in some applications, like stand-alone power plants based on discontinuous sources (solar, wind power), they are combined with electrolyzers and storage systems to form an energy storage system. The round-trip efficiency (electricity to hydrogen and back how to build a fuel cell to electricity) of such plants is between 30 and 40%.
Researchers have also managed to use diesel for fuel cells.
Efficiency
Fuel cells running on compressed hydrogen may have a power plant to wheel efficiency as low as 22% and for liquified hydrogen even 17% (efficiency of Hydrogen Fuel Cell, Diesel-SOFC-Hybrid and Battery Electric Vehicles Ulf Bossel European Fuel Cell Forum). Molten Carbonate fuel cells running on pipeline natural gas can achieve single-cycle efficiencies of approximately 50% (fuel-to-electricity) and combined heat and jaz fuel cell power efficiencies of better than 70%. Phosphoric acid fuel cells when converting waste water into steam for use to heat space or water can achieve efficiences of 80%.
Economy
GM believes that fuel cell vehicles will be available at market prices around the end of this decade. The problem is the investment for the catalyst which was 1000 USD per installed kW electric power output in 2002 (http://www.fuelcellcontrol.com/evs19.html).
History
The principle of the fuel cell was discovered by Swiss scientist Christian Friedrich Schönbein in 1838 and published in the January 1839 edition of the "Philosophical Magazine" [1]. Based on this work, methanol fuel cell the first fuel cell was developed by Welsh scientist Sir William Grove. A sketch was published in 1843, but it wasn't until 1932 that British engineer Francis Thomas Bacon developed successful fuel cell devices. In 1958, a team led by Pat catalyst for fuel cell Grimes built a 15 kW fuel cell tractor for Allis-Chalmers that was demonstrated across the US at state fairs. This system used potassium hydroxide as the electrolyte and compressed hydrogen and oxygen as the reactants. Later, in 1959, Bacon and his colleagues demonstrated a practical five-kilowatt unit capable of powering a welding machine, which led, in the 1960s to Bacon's patents being licensed direct fuel cell by Pratt and Whitney from the U.S. where the concepts were used in the U.S. space program to supply electricity and drinking water (hydrogen and oxygen being readily available from the spacecraft tanks). Extremely expensive materials were used and the fuel cells required very pure hydrogen and oxygen. Early fuel cells tended to require inconveniently high operating temperatures that were a problem in many applications. However, fuel cells were seen to be desirable due to the large amounts of fuel available (hydrogen & oxygen).
Further technological advances in the 1980s and 1990s, like the use of Nafion as the membrane electrolyte, and reductions in the quantity of expensive platinum catalyst required, have made the prospect hydrogen fuel cell car of fuel cells in consumer applications such as automobiles more or less realistic. (See Hydrogen car)
The fuel cell industry
United fuel cell companies Technologies (UTX) was the first company to manufacture fuel cells. In the 1960s the company provided NASA with fuel cells to generate electricity for the Apollo missions. UTX's UTC Power subsidiary [2] was the first company to manufacturer and commercialize a large, stationary fuel cell technology fuel cell information fuel cell system for use as a co-generation power plant in hospitals, universities, and large office fuel cell energy buildings. UTC Power continues to market this fuel cell as the PureCell 200 [3], a 200 kW system. UTC Power continues to be the sole supplier of fuel cells to NASA portable fuel cell for use in space vehicles, having supplied the Apollo missions and currently the space shuttle, and is developing fuel cells for automobiles, buses, and cell phone towers. UTC Power claims to be "the global leader in the development and production of fuel cell technology" for both transportation and on-site power markets. In the automotive fuel cell market, UTC Power demonstrated the first fuel cell capable of starting under freezing conditions with its proton exchange membrane (PEM) automotive fuel cell. Note: UTC Power also ethanol hydrogen fuel cell uses the UTC Fuel Cells [4] name when referring to fuel cell products.
Ballard Power Systems is a major manufacturer of fuel cells and claims to lead the world in automotive fuel cell technology. Ford Motor Company and DaimlerChrysler are major investors in Ballard. In 2003, most automobile companies were customers of Ballard, with only General Motors and Toyota pursuing internal development of fuel cells polymer electrolyte fuel cell for automotive use which broke fuel cell bike up in 2005; in 2004 Nissan and Honda started similar research hydrogen fuel cell technology programs. GM apparently now teams with DaimlerChrysler and BMW [5].
Perth in Western Australia is also participating in the trial with three fuel cell powered buses now operating between Perth and the port city of Fremantle. The trial is to be extended to other Australian cities over the next three years.
In late 2004, Mechanical Technology Inc.'s subsidiary, MTI MicroFuel Cells debuted its first fuel cell cars hydrogen Direct Methanol Fuel Cell (DMFC)[6] for commercial use. MTI's Mobion™ cord-free rechargeable power pack technology consists of a fuel cell which runs on 100% fuel cell batteries (neat) Methanol. MTI's Mobion line is being released in industrial, consumer, and military markets as a low-cost how to build hydrogen fuel cell for science fair replacement for lithium-ion batteries.
Advantages and disadvantages
Environmental effects
A common misconception among the public is that hydrogen is a source of energy, and that there are "mines" or "reservoirs" of hydrogen to find. However, all hydrogen is not a primary source of energy: ethanol fuel cell it is only an energy carrier, and must be manufactured using energy from other sources.
Some critics of the current stages of this technology argue that the energy needed to create the fuel in the first place may reduce the ultimate energy hydrogen fuel cell powered vehicle efficiency of the system to below that of the most fuel cell generator efficient gasoline internal-combustion engines; this is especially true if the hydrogen has to be compressed to high pressures or liquified, as it does in automobile applications (the electrolysis of water is itself a fairly efficient process). It has to be remarked, though, that even the most efficient internal-combustion engines are not very efficient in absolute terms; furthermore, gasoline is not a primary energy source either, because crude oil has to be treated in a refinery to obtain gasoline.
As an alternative to electrolysis, hydrogen catalyst in fuel cell hydrogen fuel cell can be generated from methane (the primary component of natural gas) with approximately 80% efficiency, or with other hydrocarbons to a varying degree of efficiency. The hydrocarbon-conversion method releases greenhouse gases, but, since the production is concentrated in one facility, and not distributed on every single vehicle or utility, it is possible to separate the gases and dispose of them properly, for example by injecting them in an oil or fuel cell cars gas reservoir. portable power fuel cell A CO2 injection project has been started by Norwegian company Statoil in the North Sea, at the Sleipner field. [7]
Other types of fuel cells do not face these problems, however. For example, biological fuel cells take glucose and methanol from food scraps and fuel cell catalyst convert it into hydrogen and food for the bacteria.
However, another environmental problem hydrogen fuel cell batteries faced by fuel cell vehicles all types of hydrogen fuel cells has been pointed out in a paper published in Science magazine by a group of Caltech scientists. They note that if hydrogen fuel cell usage becomes hydrogen fuel cell technologies widespread enough to replace gasoline internal-combustion engines, small amounts of hydrogen leaking from storage containers and pipelines will have a detrimental impact on the Earth's ozone layer. However, their findings remain controversial, and their assumptions regarding educational fuel cell the amount of hydrogen leaked have been disputed by industry officials.
Fuel cell design issues
To make fuel cells economically competitive, there are many practical problems to be overcome as well. Water management remains a key problem in Proton Exchange Membrane Fuel Cells (PEMFCs), where generated water will need to be disposed of. Not enough water and the polymer loses its ability to conduct protons across the cell; too much water in the fuel cell and the electrodes will flood, stopping the reaction. Methods to dispose hydrogen fuel cell vehicles of the hydrogen fuel cell cars excess water are fuel cell research being developed by fuel cell companies.
At the same time many other variables must be juggled, including temperature throughout the cell (which changes and can sometimes destroy a cell through thermal loading), reactant and product levels at various cells. Materials must be chosen pem fuel cell proton exchange membrane to do various tasks which none fill completely. Durability and lifetime of the cells can be serious issues for some cells, low power densities for others. Putting all of these factors together hasn't fuel cell battery been accomplished decisively yet, and remains how phone fuel cell does a fuel cell work the challenge.
In vehicle usage, many problems are amplified. For instance, cars must be required to start fuel cell vehicle in any weather conditions a person can reasonably expect to encounter: about 80% of the world's car park is legally subject to the requirement of being able to start from sub-zero temperatures. Fuel cells have no difficulty operating in the hottest locations, but the coldest do present a problem. UTC Power was the first company to demonstrate an automotive fuel cell capable of starting in freezing temperatures, and Honda's FCX was the first fuel cell powered vehicle to do so, but temperatures enzyme fuel cell below -20 degrees Celsius still prohibit the fuel cell stack from starting.
Fuel cell applications
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Fuel cells are very useful as power sources in remote fuel cell locations, such alcohol fuel cell as spacecraft, remote weather stations, large parks, rural locations, and in certain military applications. A fuel cell system running on hydrogen can be compact, lightweight and has no major moving parts.
A near-term application is combined heat and power (CHP) for office buildings and factories. This type of system generates constant electric power (selling excess power back to the grid when it is not consumed), and at the same time produce hot air and water from the waste heat. Phosphoric-acid fuel cells (PAFC) comprise the largest segment of existing CHP products worldwide and can provide efficiencies close to 80%. The largest manufacturer of PAFC fuel cells is UTC Power, a division of United Technologies Corporation. As of 2005, there were close to 300 UTC Power "PureCell" 200 kilowatt units in service globally. Molten-carbonate fuel cells have also been installed in these applications, and Solid-oxide fuel cell prototypes exist.
Because fuel cells have a high cost per kilowatt, molten carbonate fuel cell and because their efficiency decreases with increasing power density, they are usually not considered for applications with high load variations. In particular, they are not suited for energy storage systems in small and medium scale. An electrolyzer and fuel cell would return less than 50 percent of the input energy (this is known as round-trip efficiency), while a much cheaper lead-acid battery might return about 90 percent.
However, since fuel cell/electrolyzer systems do not store fuel, but rather rely on external storage units, they can be successfully applied in large-scale energy storage, rural areas being one example. In this case, batteries would have to be largely oversized to meet the storage demand, but fuel cells only need a larger storage unit (typically cheaper than an electrochemical device).
The use of fuel cells for cogeneration of electricity and hot water in households is a potential long-term application, with various pilot programs launched in 2005 across the industry.
Hydrogen vehicles and refuelling
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The first hydrogen refuelling station was opened in Reykjavík, Iceland on April 2003. This station serves three buses built by DaimlerChrysler that are in service in the public transport net of Reykjavík. The station produces the hydrogen it needs by itself, with an electrolysing unit (produced by Norsk Hydro), and does not need refilling: all that enters is electricity and water. Shell is also a partner in the project. The station has no roof, in order to allow any leaked hydrogen to escape to the atmosphere.
There are numerous prototype or production cars and buses based on fuel cell technology being researched or manufactured. Research is ongoing at companies like BMW, Hyundai, and Nissan, among many others. build your own fuel cell However, a practical commercial automobile is not expected until at least 2010 according to the industry. There are, however, fuel cell-powered buses currently active or in production, such as a fleet of Thor buses with UTC Power fuel cells in California, operated by SunLine Transit Agency [8].
Currently, a team of college students called Energy-Quest is planning to take a hydrogen fuel cell powered boat around the world (as well as other projects using efficient or renewable fuels). Their venture is called the Triton.
Suggested applications
- baseload utility power plants
- cellular phone power
- electrically-powered vehicles
- emergency backup power
- off-grid power storage
- portable electronics
See also
Types of fuel cells
- Alkaline fuel cells
- Direct-methanol fuel cell
- Molten-carbonate fuel cells
- Phosphoric-acid fuel cells
- Proton-exchange fuel cell
- Reversible fuel cell
- Direct borohydride fuel cells
- Solid-oxide fuel cells
- Zinc fuel cells
External links
- PhysicsWorld: Fuel cells
- How Hydrogen Can Save America (Wired Magazine)
- How Stuff Works: Fuel Cells
- Fuel-Cells.org
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Electronics Topics
The field of electronics is the study and use of systems that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors. The design and construction of electronic circuits to solve practical problems is part of the fields of electronic engineering, and the hardware design side of computer engineering. The study of new semiconductor devices and their technology is sometimes considered as a branch of physics.
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