Wednesday, March 26, 2008
Polymer Electrolyte Membrane (PEM) fuel cells
There are several kinds of fuel cells, but Polymer Electrolyte Membrane (PEM) fuel cells—also called Proton Exchange Membrane fuel cells—are the type typically used in automobiles. A PEM fuel cell uses hydrogen fuel and oxygen from the air to produce electricity.
Fuel cell design issues
- Costs. In 2002, typical cells had a catalyst content of US$1000 per kilowatt of electric power output. In 2008 UTC Power has 400kw Fuel cells for $1,000,000 per 400kW installed costs. The goal is to reduce the cost in order to compete with current market technologies including gasoline internal combustion engines. Many companies are working on techniques to reduce cost in a variety of ways including reducing the amount of platinum needed in each individual cell. Ballard Power Systems have experiments with a catalyst enhanced with carbon silk which allows a 30% reduction (1 mg/cm² to 0.7 mg/cm²) in platinum usage without reduction in performance.[4]
- The production costs of the PEM (proton exchange membrane). The Nafion® membrane currently costs €400/m². This, and the Toyota PEM and 3M PEM membrane can be replaced with the ITM Power membrane (a hydrocarbon polymer), resulting in a price of ~€4/m². in 2005 Ballard Power Systems announced that its fuel cells will use Solupor®, a porous polyethylene film patented by DSM.[5][6]
- Water and air management[7] (in PEMFCs). In this type of fuel cell, the membrane must be hydrated, requiring water to be evaporated at precisely the same rate that it is produced. If water is evaporated too quickly, the membrane dries, resistance across it increases, and eventually it will crack, creating a gas "short circuit" where hydrogen and oxygen combine directly, generating heat that will damage the fuel cell. If the water is evaporated too slowly, the electrodes will flood, preventing the reactants from reaching the catalyst and stopping the reaction. Methods to manage water in cells are being developed like electroosmotic pumps focusing on flow control. Just as in a combustion engine, a steady ratio between the reactant and oxygen is necessary to keep the fuel cell operating efficiently.
- Temperature management. The same temperature must be maintained throughout the cell in order to prevent destruction of the cell through thermal loading. This is particularly challenging as the 2H2 + O2 -> 2H20 reaction is highly exothermic, so a large quantity of heat is generated within the fuel cell.
- Durability, service life, and special requirements for some type of cells. Stationary applications typically require more than 40,000 hours of reliable operation at a temperature of -35 °C to 40 °C, while automotive fuel cells require a 5,000 hour lifespan (the equivalent of 150,000 miles) under extreme temperatures. Automotive engines must also be able to start reliably at -30 °C and have a high power to volume ratio (typically 2.5 kW per liter).
- Limited carbon monoxide tolerance of the anode.
Meeting fuel cell vehicle Challenges Together
Automakers, fuel cell developers, component suppliers, government agencies, and others are working hard to accelerate the introduction of FCVs. Partnerships such as the DOE-led FreedomCAR initiative and the California Fuel Cell Partnership have been formed to encourage private companies and government agencies to work together to move these vehicles toward commercialization.
FreedomCAR
- Cheaper to operate
- Pollution-free
- Competitively priced
- Free from imported oil
California Fuel Cell Partnership (CaFCP)
The California Fuel Cell Partnership is a collaboration of auto companies, fuel providers, fuel cell technology companies, and government agencies demonstrating fuel cell electric vehicles in California under day-to-day driving conditions. The goals of the partnership are to test and demonstrate the viability of FCVs and related technology under real-world conditions, move them toward commercialization, and increase public awareness. The Partnership expects to place about 60 FCVs and fuel cell buses on the road by 2003.http://www.fueleconomy.gov/feg/fuelcell.shtml
Fuel cell design
n essence, a fuel cell works by catalysis, separating the component electrons and protons of the reactant fuel, and forcing the electrons to travel through a circuit, hence converting them to electrical power. The catalyst is typically comprised of a platinum group metal or alloy. Another catalytic process takes the electrons back in, combining them with the protons and the oxidant to form waste products (typically simple compounds like water and carbon dioxide). 
Condensation of water produced by a PEMFC on the air channel wall. The gold wire around the cell ensures the collection of electric current.[2]
In the archetypal hydrogen–oxygen proton exchange membrane fuel cell (PEMFC) design, a proton-conducting polymer membrane, (the electrolyte), separates the anode and cathode sides. This was called a "solid polymer electrolyte fuel cell" (SPEFC) in the early 1970s, before the proton exchange mechanism was well-understood. (Notice that "polymer electrolyte membrane" and "proton exchange membrane" result in the same acronym.)
On the anode side, hydrogen diffuses to the anode catalyst where it later dissociates into protons and electrons. These protons often react with oxidants causing them to become what is commonly reffered to as multi-facilitated proton membranes (MFPM). 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 electrically insulating. On the cathode catalyst, oxygen molecules react with the electrons (which have traveled through the external circuit) and protons to form water — in this example, the only waste product, either liquid or vapor.
In addition to this pure hydrogen type, there are hydrocarbon fuels for fuel cells, including diesel, methanol (see: direct-methanol fuel cells) and chemical hydrides. The waste products with these types of fuel are carbon dioxide and water.
The materials used in fuel cells differ by type. The electrode–bipolar plates are usually made of metal, nickel or carbon nanotubes, and are coated with a catalyst (like platinum, nano iron powders or palladium) for higher efficiency. Carbon paper separates them from the electrolyte. The electrolyte could be ceramic or a membrane.
A typical PEM fuel cell produces a voltage from 0.6 V to 0.7 V at full rated load. Voltage decreases as current increases, due to several factors:
- Activation loss
- Ohmic loss (voltage drop due to resistance of the cell components and interconnects)
- Mass transport loss (depletion of reactants at catalyst sites under high loads, causing rapid loss of voltage)[3]
To deliver the desired amount of energy, the fuel cells can be combined in series and parallel circuits, where series yield higher voltage, and parallel allows a stronger current to be drawn. Such a design is called a fuel cell stack. Further, the cell surface area can be increased, to allow stronger current from each cell.
http://en.wikipedia.org/wiki/Fuel_cellfuel cell vehicles (FCVs)
This emerging technology has the potential to significantly reduce energy use and harmful emissions, as well as our dependence on foreign oil. FCVs will have other benefits as well.
A Radical Departure
FCVs represent a radical departure from vehicles with conventional internal combustion engines. Like battery-electric vehicles, FCVs are propelled by electric motors. But while battery electric vehicles use electricity from an external source (and store it in a battery), FCVs create their own electricity. Fuel cells onboard the vehicle create electricity through a chemical process using hydrogen fuel and oxygen from the air.
FCVs can be fueled with pure hydrogen gas stored onboard in high-pressure tanks. They also can be fueled with hydrogen-rich fuels; such as methanol, natural gas, or even gasoline; but these fuels must first be converted into hydrogen gas by an onboard device called a "reformer."
FCVs fueled with pure hydrogen emit no pollutants; only water and heat; while those using hydrogen-rich fuels and a reformer produce only small amounts of air pollutants. In addition, FCVs can be twice as efficient as similarly sized conventional vehicles and may also incorporate other advanced technologies to increase efficiency.
Fuel cell
A fuel cell is an electrochemical energy conversion device. It produces electricity from various external quantities of fuel (on the anode side) and oxidant (on the cathode side). These react in the presence of an electrolyte. Generally, the reactants flow in and reaction products flow out while the electrolyte remains in the cell. Fuel cells can operate virtually continuously as long as the necessary flows are maintained.
Fuel cells are different from batteries in that they consume reactant, which must be replenished, while batteries store electrical energy chemically in a closed system. Additionally, while the electrodes within a battery react and change as a battery is charged or discharged, a fuel cell's electrodes are catalytic and relatively stable.
Many combinations of fuel and oxidant are possible. A hydrogen cell uses hydrogen as fuel and oxygen as oxidant. Other fuels include hydrocarbons and alcohols. Other oxidants include air, chlorine and chlorine dioxide.
http://en.wikipedia.org/wiki/Fuel_cell
Fuel cell applications
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, forklifts, 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. Telecommunications companies are installing fuel cells at cell phone, radio and 911 towers. The possibilities are endless.
Stationary
More than 2500 fuel cell systems have been installed all over the world — in hospitals, nursing homes, hotels, office buildings, schools, utility power plants - 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.
Transportation
Auxiliary Power Units (APUs) - Today’s heavy-duty trucks are equipped with a large number of electrical appliances–from heaters and air conditioners to computers, televisions, stereos, even refrigerators and microwaves. To power these devices while the truck is parked, drivers often must idle the engine. The Department of Energy (DOE) has estimated the annual fuel and maintenance costs of idling a heavy-duty truck at over $1,800 and that using fuel cell APUs in Class 8 trucks would save 670 million gallons of diesel fuel per year and 4.64 million tons of CO2 per year.
Portable Power
Micro Power
Fuel cell FAQ
- When was the fuel cell invented?
- Fuel cells were initially demonstrated in 1839, by Sir William Grove. However, a truly workable fuel cell was not demonstrated until 1959. After use in NASA's space programme, interest in fuel cells died down somewhat until the 1990s when research and development started to lead towards greater prospects of commercialisation.
- Which fuels can be used in a fuel cell?
- Most fuel cells use hydrogen at the point where the electrochemical reaction takes place. This hydrogen can be chemically generated or reformed from a variety of normal fuels, including gasoline, natural gas or methanol. There is no consensus as to the single best fuel.
- What types of fuel cells are there?
- There are a number of types of fuel cell which are normally distinguished by the electrolyte they contain. The best-known types are alkaline, molten carbonate, phosphoric acid, proton exchange membrane and solid oxide. Direct methanol and regenerative fuel cells are also being extensively researched.
- What is a fuel cell?
- A fuel cell is an electrochemical device that produces electricity and heat from a fuel (often hydrogen) and oxygen. Unlike a conventional engine, it does this without burning the fuel and can therefore be more efficient and cleaner.
- Can I buy a fuel cell?
- In general, fuel cells are in the development phase and are not yet commercially available. Many companies are currently running field trials of alpha and beta development units and hope to be commercialising this technology from as early as this year in some cases. However, some products, such as educational fuel cells, are commercially available now, as listed in our
- Why use a fuel cell?
- Fuel cells have a number of advantages over other technologies for power generation. They have the potential to use less fuel than competing technologies and to emit no pollution when used. There are also many reasons why a fuel cell might be useful in specific environments, such as the high quality of electricity generated or their quiet operation.
- What devices could a fuel cell power?
- In principle, a fuel cell could power any device that requires electrical energy to function. This could range from a mobile phone up to a factory. Presently, the majority of attention is focussed on powering automobiles, houses and medium-sized portable electrical equipment. However, announcements have suggested that portable computers may be an early application.
- How much does a fuel cell cost?
- Since fuel cells are not yet fully commercialised, they are produced in small numbers. Consequently, they tend to be more expensive than they will be when selling in significant quantities. However, as technology improves, cost reduction is proceeding towards meeting challenging cost targets set by the automotive industry. People involved in the industry generally believe that this can be accomplished and that in any case, costs will continue to decrease and will be significantly lower by the end of this decade than they are now.
- What is the difference between a fuel cell and a battery?
- Whilst a battery chemically stores and releases electricity, a fuel cell produces energy by reacting a fuel with air. A battery will therefore run out of power and have to be recharged or disposed of. A fuel cell, however, will continue to function and produce power as long as the fuel and oxygen are supplied to it.
- Is hydrogen safe?
- Like any other fuel, hydrogen is potentially dangerous and is flammable. However, so are gasoline, diesel and natural gas and this has not prevented their use to power cars, alongside the correct safety features. Hydrogen even has some advantages as it is non-toxic, a definite benefit over most fuels. Use of hydrogen would therefore present new but not insurmountable safety challenges.
- Why not burn hydrogen instead of using it in a fuel cell?
- Hydrogen is an extremely clean-burning fuel. However, any combustion process will produce small amounts of pollutants whereas a fuel cell has the potential to emit none. In addition to this, a fuel cell can inherently be more fuel-efficient than an internal combustion engine. However, there may be applications where burning hydrogen makes sense and it is possible to imagine that hydrogen fuel cell powered cars and hydrogen internal combustion engine powered cars could run side-by-side on the roads.
- Are fuel cells a renewable energy source?
- Fuel cells themselves are not a power source: rather they use a fuel to produce power. If this fuel is obtained from renewable sources, then fuel cells can be an important part of the energy chain, perhaps with hydrogen being used to store intermittent energy and fuel cells converting this hydrogen back to power when required.
What is a fuel cell?
A fuel cell is an electrochemical device that combines hydrogen and oxygen to produce electricity, with water and heat as its by-product. As long as fuel is supplied, the fuel cell will continue to generate power. Since the conversion of the fuel to energy takes place via an electrochemical process, not combustion, the process is clean, quiet and highly efficient – two to three times more efficient than fuel burning.
No other energy generation technology offers the combination of benefits that fuel cells do. In addition to low or zero emissions, benefits include high efficiency and reliability, multi-fuel capability, siting flexibility, durability, scalability and ease of maintenance. Fuel cells operate silently, so 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 or office.
Sony Bravia KDL-40D3500
What’s inside your BRAVIA TV?
Technologies that make a difference
Selected BRAVIA TV models offer important benefits.
Motionflow +100Hz
Go with the flow
Standard on BRAVIA X series models and the BRAVIA D3000 model, Motionflow +100Hz technology has a really important job. It captures all the detail and drama of fast-moving action scenes, such as sports, and makes them ultra smooth.
Motionflow works by doubling up the number of frames you see on screen. New ones are inserted into fast-moving sequences, like the flight of a ball for instance, to smooth out the motion.
Based on information it gets from the before and after frames in every sequence, Motionflow cleverly creates brand new pictures to do this. So existing frames aren’t just copied and doubled up.
24p True Cinema
To display the film, they have to double the original number of frames by duplicating existing ones and speeding the film up, which noticeably distorts synchronisation. They even raise the pitch of the actors’ voices.
24p True Cinema matches the original speed to capture the power and quality of the studio recording.
The 24p format is detected by your Blu-ray Disc player or PLAYSTATION®3 and outputted directly to the TV in 24 frames per second. What you see is exactly how it was originally recorded.
Cinema Mode and Theatre Mode
Sony KDL-40D3500 Review
Design
The KDL-40D3500 is the embodiment of Sony's design philosophy with a chic matte black understated presence that simply oozes class. Build quality is back to its very best with the Sony looking like it could have been sculpted from a solid block of metal.
Features
A change in model number from 3000 to 3500 would suggest that the KDL-40D3500 represented a relatively minor upgrade from its predecessor the KDL-40D3000. However, the changes in specification are more wide ranging than you would imagine.
Screen: 40in 16:9 Tuner: Digital Sound System: Nicam Resolution: 1920 x 1080 Contrast Ratio: 1800:1 (16,000 dynamic) Brightness: 450cd/m2 Other Features: Bravia Picture Processing Engine, Live Colour Creation, 24p True Cinema. Sockets: 2 HDMI, 2 SCART, Component Video, Composite Video, PC input.
To begin with, the 40D3500 gains a Full HD (1920 x 1080) resolution which can potentially give a marked improvement in the display of sources such as Sky Tv (1080i). The 1080 lines of resolution match the resolution of the screen negating the need for any picture scaling to fit. If you have a device which outputs pictures in the superior 1080p (e.g. Sony's PlayStation 3) the 3500 can accept those pictures in their full glory.
'Motionflow +100Hz' technology (featured on the 40D3000) which doubles the number of frames shown from 50 to 100 by interpolating an extra frame in between each source frame does not feature on the 40D3500.
With 2 HDMI inputs, the 3500 has one less than the 3000 model. Otherwise, the specification of both screens are largely similar.
The Sony 40D3500 is equipped with '24p True Cinema' which enables the panel to display films at their intended 24fps (frames per second).
Alongside 24p True Cinema is Sony's 'Theatre Mode' technology which adjusts colour, contrast and brightness settings to makes movies look as authentic as the original.
It is worth mentioning that the 24p mode comes into its own with High Definition (Blu-ray or HD DVD) players which allow you to play movies at their original speed. The original 'cine' film is generally recorded at 24 frames per second, which in the absence of '24p True Cinema' is speeded up to 25 (standard for most TV's) frames per second with an accompanying increase in audio pitch.
Colour reproduction on the KDL40D3500 should offer smoother transitions than previous Sony LCD's with a new 10-bit panel offering 1024 shades of gradation.
Theatre Sync, which is Sony's name for CEC (Consumer Electronic Control), is a control standard that functions over HDMI 1.3. The technology facilitates one-touch control over compatible devices and in practice means that if you fire up your compatible DVD player, the all connected devices such as your LCD TV will also spring into life.
Sonically, the KDL-40D3500 comes equipped with Sony's S-Force Front Surround which is their latest virtual surround sound technology.
Performance
Although specification has changed considerably between the 3500 and 3000 models, performance comparisons reveal a not so dramatically differing performance.
As with the previous model, High Definition (HD) is where the Sony KDL-40D3500 excels. Hook up a 1080p capable source however, and you have even more pristine pictures. The KDL-40D3500 displays a clarity and sharpness that make you want to reach out and touch objects or people as they glide across the screen. Colours are wonderfully vibrant and reach a level of authentic realism to match any LCD.
Although black levels are still behind the best that plasma can offer, the KDL-40D3500 has made great strides in this area from previous Sony's. Shadow detailing now takes on a subtlety which is a match for any 40in LCD currently out there.
Again, Standard Definition (SD) performance suffers to a degree from some of the inconsistencies that creep into a picture as a result of the conversion of a 576p source to an HD ready screen configuration.
The effectiveness of Sony's Motionflow +100Hz has always been open to question, and the fact that the 40D3500 does not seem to suffer too much from its departure suggests that this technology is not quite the complete article as yet. There was some evidence of a little more motion blur and shimmering than on the 3000, and the picture did appear to be very slightly 'grainy', but not to any great degree. The picture quality is still pretty good, but you'll have a hard time shifting down from HD because the picture is so outstanding in this respect.
Finally, if there is a 40in LCD TV out there with a richer or more precise colour palette, we have yet to see it. The range, depth and subtlety in this respect is simply outstanding. The most intricate of detailing such as skin tone is realised with class leading performance.
Conclusion
The Sony KDL-40D3500 is a highly accomplished performer when it comes to High Definition material. However, if SD viewing is just as important there are better performers out there.
| 40in LCD | |||||||||||
| |||||||||||
| Peerless HD performance tempered by slightly disappointing SD pictures. | |||||||||||
| HD Ready: | yes | ||||||||||
| Resolution: | 1920 x 1080 | ||||||||||
| Rating: | 89% | ||||||||||
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