洒精怎么发电?
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燃料电池
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燃料电池，是一种使用燃料进行化学反应产生电力的装置，最常见的是氢氧燃料电池，由于价格低廉无危害并且产生的废物——水可以供人使用，所以最早被应用于太空。现在也有一些笔记型电脑开始研究使用燃料电池。但由于产生的电量太小，且无法瞬间提供大量电能，只能用于平稳供电上。
编写途中 “燃料电池”是与科学技术相关的未完成小作品。欢迎您积极编辑或修订扩充其内容。
取自"http://wikipedia.cnblog.org/wiki/%E7%87%83%E6%96%99%E7%94%B5%E6%B1%A0"
页面分类: 科学技术小作品 | 电池
Fuel cell
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For other uses, see Fuel cell (disambiguation).
A fuel cell is an electrochemical device similar to a battery, but differing from the latter in that it is designed for continuous replenishment of the reactants consumed; i.e. it proces 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). Typically in fuel cells, reactants flow in and reaction procts flow out, and continuous long-term operation is feasible virtually as long as these flows are maintained.
Fuel 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 methane or natural gas that generate carbon dioxide. The only by-proct 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 rece fossil fuel dependence.
Contents
[hide]
* 1 Science
* 2 Efficiency
* 3 Economy
* 4 History
* 5 The fuel cell instry
* 6 Advantages and disadvantages
o 6.1 Environmental effects
o 6.2 Fuel cell design issues
o 6.3 Fuel cell applications
o 6.4 Hydrogen vehicles and refuelling
* 7 Suggested applications
* 8 See also
o 8.1 Types of fuel cells
* 9 External links
[edit]
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 archetypical example of a hydrogen/oxygen proton-exchange membrane (or "polymer electrolyte") fuel cell (PEMFC), a proton-concting 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 concted 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 proct is water vapor and/or liquid 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 to electricity) of such plants is between 30 and 40%.
Researchers have also managed to use diesel for fuel cells.
[edit]
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 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%.
[edit]
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).
[edit]
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, the first fuel cell was developed by Welsh scientist Sir William Grove. A sketch was published in 1843, but it wasn't until 1959 that British engineer Francis Thomas Bacon developed successfully a 5 kW stationary fuel cell. In 1959, a team led by Harry Ihrig 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 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 e 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 rections in the quantity of expensive platinum catalyst required, have made the prospect of fuel cells in consumer applications such as automobiles more or less realistic. (See Hydrogen car)
[edit]
The fuel cell instry
United 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 system for use as a co-generation power plant in hospitals, universities, and large office 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 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 proction 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 uses the UTC Fuel Cells [4] name when referring to fuel cell procts.
A fuel cell powered vehicle designed by General Motors
Enlarge
A fuel cell powered vehicle designed by General Motors
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 for automotive use which broke up in 2005; in 2004 Nissan and Honda started similar research 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 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% (neat) Methanol. MTI's Mobion line is being released in instrial, consumer, and military markets as a low-cost replacement for lithium-ion batteries.
[edit]
Advantages and disadvantages
[edit]
Environmental effects
A common misconception among the public is that elemental hydrogen is a source of energy, and that there are "mines" or "reservoirs" of hydrogen to find. This is simply not true, hydrogen is not a primary source of energy: it is only an energy storage medium, and must be manufactured using energy from other sources.
The physical laws relating to the conservation of energy unfortunately create a situation where the energy needed to create the fuel in the first place may rece the ultimate energy efficiency of the system to below that of the most 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). However, even the most efficient internal-combustion engines are not very efficient in absolute terms; furthermore, gasoline is not a primary energy source, because crude oil has to be treated in a refinery to obtain gasoline.
As an alternative to electrolysis, hydrogen 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 proction 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 gas reservoir. 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 convert it into hydrogen and food for the bacteria.
However, another environmental problem faced by 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 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 the amount of hydrogen leaked have been disputed by instry officials.
Finally, roughly 70% of all electricity proced in the United States comes from Coal. The problem is that coal is a relatively dirty energy source. If electrolysis (a process that uses electricity) is used to create hydrogen using energy from power plants, it is essentially creating hydrogen fuel from coal. Though the fuel cell itself will only emit heat and water as waste, the problem of pollution is still present at power plants.
[edit]
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 or (PEMFCs), where generated water will need to be disposed of. Not enough water and the polymer loses its ability to conct protons across the cell; too much water in the fuel cell and the electrodes will flood, stopping the reaction. Methods to dispose of the excess water are 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 proct levels at various cells. Materials must be chosen 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 been accomplished decisively yet, and remains the challenge.
In vehicle usage, many problems are amplified. For instance, cars must be required to start 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. Honda's FCX was the first fuel cell powered vehicle to do so, but temperatures below -20 degrees Celsius still prohibit the fuel cell stack from starting.
[edit]
Fuel cell applications
For more details on this topic, see Hydrogen economy.
Fuel cells are very useful as power sources in remote locations, such 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 proce hot air and water from the waste heat. Phosphoric-acid fuel cells (PAFC) comprise the largest segment of existing CHP procts worldwide and can provide combined efficiencies close to 80% (45-50% electric + remainder as thermal). 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, 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 instry.
[edit]
Hydrogen vehicles and refuelling
For more details on this topic, see Hydrogen vehicle.
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 proces the hydrogen it needs by itself, with an electrolysing unit (proced 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 proction 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. However, a practical commercial automobile is not expected until at least 2010 according to the instry. There are, however, fuel cell-powered buses currently active or in proction, 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.
[edit]
Suggested applications
* Baseload utility power plants
* Cellular phone power
* Electrically-powered vehicles
* Emergency backup power
* Off-grid power storage
* Portable electronics
[edit]
See also
[edit]
Types of fuel cells
* Alkaline fuel cell
* Biological fuel cell
* Direct borohydride fuel cell
* Direct-methanol fuel cell
* Formic acid fuel cell
* Molten-carbonate fuel cell
* Phosphoric-acid fuel cell
* Proton-exchange fuel cell
* Reversible fuel cell
* Solid-oxide fuel cell
* Zinc fuel cell ('Air' fuel cell)
[edit]
External links
* PhysicsWorld: Fuel cells
* How Hydrogen Can Save America (Wired Magazine)
* How Stuff Works: Fuel Cells
* Fuel-Cells.org
Retrieved from "http://en.wikipedia.org/wiki/Fuel_cell"
Categories: Energy conversion | Fuel cells | Electrochemistry | Alternative propulsion | Alternative energy
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