In essence, the fuel cell creates an electrical current with the electrochemical combination of hydrogen atoms (the source of which can be natural gas, methanol, or petroleum) and oxygen (from the air). A fuel cell developed by Ballard Power Systems in BC is called a "Proton Exchange Membrane Fuel Cell". The fuel cell has no moving parts and uses a fraction of the fuel that a normal motor does. In fact, it is possible to use pure hydrogen in the cell, with the only by-product then the harmless combination of hydrogen and oxygen: Water.

Fuel cells can be used in automobiles, to heat houses, for use in industry (in British Columbia fuel cells have been used to kiln-dry lumber, very important in the forestry sector), and as emergency power sources.

In racing, a fuel cell is a type of fuel tank designed not to rupture in the event of an impact. Fuel cells were first develped from aircraft self-sealing fuel tanks, which were designed not to leak after combat damage.

Fuel cell development really began in the 1960s, when quite a number of racers died because of burns, most notably Fireball Roberts at Darlington in 1964 and Lorenzo Bandini at Monaco in 1967. Early racing fuel tanks were prone to rupture after a serious impact, spilling the entire contents quickly. Given the volatility of racing fuel and the profusion of hot parts and sparks after an accident, fire was always a serious danger. The danger hit home after Swede Savage crashed while leading the Indianapolis 500 in 1973. His agonized face, while he stared at the burns that would take his life were plastered across many papers.

There are several parts to the modern fuel cell. First is the container, which is generally metal, but may be made of rotary molded plastic. Inside is a flexible rubber bladder, which is capable of deforming under impact and penetration resistant. Inside that you have foam blocks, really they resemble a very sparse sponge and it is designed to both pass fuel but somewhat plug any penetration. The foam offers the additional benefit of reducing the amount of 'fuel slosh' inside the cell as the car turns.

All perforations, including the refueling cap, tank vent and fuel pickup are guarded either by flapper valves or ball valves to seal the tank in the event of a rollover.

Fuel cells have been extraordinarily successful in practice, particularly when used with modern fire extinguishers and SFI rated firesuits. Driver deaths by fire, once commonplace, are now very, very rare.

A fuel cell is a device that converts a fuel, such as hydrogen, natural gas, methanol or propane to electricity. There are no moving parts such as in traditional setups for power generation (boiler, turbine generator), resulting in high efficiencies up to approximately 80%.

Fuel cells and batteries have much in common. They both contain two electrodes and function on the principle of a chemical reduction/oxidation reaction (redox reaction). However, a fuel cell typically runs on a liquid or gaseous fuel and oxidizer that is fed from outside of the cell, whereas a battery stores its solid fuel and oxidizer on plates inside the cell.

A schematic of a fuel cell is given below. The cell consists of two electrodes, an anode and a cathode. The anode part is fed with the fuel, for instance hydrogen. The anode itself consists of a porous, conductive material such as carbon with a metal catalyst (typically, finely dispersed platinum.) At the anode, the feed gas is reacted to protons (H+) and electrons (e-.) The protons migrate through an electrolyte, which can either be a liquid (KOH / H2SO4), or a conductive polymer membrane (the so called PEM, Polymer Electrolyte Membrane.) The electrons leave the anode, perform work (e.g. operate an electric motor), and enter the cathode. At the cathode, oxygen is dissociated and reacted with the protons to form water.


      Anode          Cathode
      Feed   e- ->    Feed
       H2   ________  O2
            |      |
      _| |__| _____|__| |_
     |     |/|- - |/|     |
     |     |/| - -|/|     |
     |     |/|Elec|/|     |
     |     |/| tro|/|     |
     |     |/|lyte|/|     |
     |     |/| - -|/|     |
     |     |/|- - |/|     |
     |     |/| - -|/|     |
     |     |/|- - |/|     |
     |_   _|_|____|_|_   _|
       | |            | |

      Anode         Cathode
      Vent           Vent
       H2           O2 + H2O
The partial (redox) reactions in the fuel cell are as follows:
Anode:     H2 -> 2 H+ + 2 e-

Cathode:   O2 -> 2 O
           2 H+ + O + 2 e- -> H2O

A single H2/O2 fuel cell operates at approximately 0.7 volt. Manufacturers arrange multiple cells in series to provide the desired electrical output. The theoretical efficiency (Free Energy/Enthalpy) of this reaction is approximately 82.9%. Thus, more than 80% of the chemical energy can be converted into electricity. Practical efficiencies range from 40-80%, but this is still much higher than the 25-40% obtained in steam turbines/generators.

The concept of fuel cells isn't new; it is almost as old as the field of electrochemistry itself. However, the first practical fuel cells were developed in the 1960s for the Gemini and Apollo Space programs. Fuel cell systems were advantageous for spacecraft, since hydrogen was already present as rocket propellant, and the fuel cell provided both electricity and drinking water to the astronauts. Fuel cells are also in use in the Space Shuttle program.

Since the 1970s, fuel cells have also been used as power generators for commercial buildings. This application has gained significant interest over the last 10 years. The army is also investigating fuel cell technology as means of portable power for combat needs. There is a lot of development on (PEM) fuel cells for automotive applications, because of the low emissions and high efficiency.

While fuel cell technology offers great promises for the future, there are still several hurdles that need to be overcome. The first problem is that of fuel storage. Especially for automotive applications, storage of hydrogen in the form of a compressed gas is dangerous. Cryogenic liquid hydrogen is expensive, and also dangerous when the vehicle is involved in an accident. Several researchers are looking into safer means of storing hydrogen: binding it as a metal hydride, or adsorbing it on carbon nanofibers. The storage capacity of these alternatives is still relatively low.

Currently, several companies are investigating using regular gasoline as a hydrogen source for fuel cells. The fuel is processed by steam reforming, before it enters the fuel cell:

  CnHm + n H2O -> n CO + (m/2 + n) H2
  CO + H2O -> CO2 + H2

This reaction can be conducted with a high conversion and yield, and it has the advantage that a wide range of fuels can be used. Regular gasoline is advantageous, since this would require little changes to the current gasoline distribution network. Methanol (CH3OH) is a good alternative fuel, because of its high hydrogen content. Ethanol (ethyl alcohol) could be synthesized by biochemical means. However, a major problem is the presence of small amounts of unreacted carbon monoxide (CO) in the feed stream of the fuel cell. The carbon monoxide acts as a poison to the platinum catalysts at concentrations as low as 100 ppm. Some researchers are investigating direct-methanol fuel cells that oxidize the liquid feed directly, but these systems currently have a relatively low efficiency.

A second issue is cost. Regular combustion engines are much cheaper to build and do not require expensive platinum catalysts to operate. There is a lot of development on fuel cells that use less of the precious metal, or cheaper alternative catalysts. A car using 1980s technology would require approximately $30 000 worth of platinum. Currently, only $400 of the precious metal would be required.

Finally, reliability is also very important for automotive applications. Catalysts can deactivate due to impurities in the fuel as was already mentioned, but also due to sintering and agglomeration. The lifetime of the polymer membrane is also an important consideration.

Fuel cells have a promising future for localized power generation and automotive applications. However, a widespread acceptance of the technology (the "Hydrogen Economy") requires a viable supply of appropriate fuel, lower manufacturing costs, and higher performances.

The newest advancement in hydrogen fuel cells may actually be from laundry detergent. Instead of the fuel being made up of natural gas, the hydrogen atoms will be bonded to borax, rendering the fuel non-explosive (the main concern of most potential consumers). The hydrogen atoms are freed from the borax bonds by water. The only other chemical needed is sodium, which will bond with the borax and the oxygen, from the water, to form sodium borate (NaBO2). That, and some left-over borax, would be the only exhaust products. This process is currently(as of March 2002) under testing for a possible Chrysler van.

Should testing go well, we may soon see fuel cells on the road, with no carbon monoxide or dioxide exaust to worry about.

Fuel Cell Technology

Whenever there is an energy crisis or oil shortage, there is always talk about alternative methods of power other than the use of oil. One of the most talked about technologies is fuel cell technology. This is not to say that fuel cells are a new concept fresh from the drawing board, but in fact the idea is a well-proven and well-used method of producing electricity. There are many types of fuel cells, each with benefits, each with limitations. The use of fuel cells to power vehicles, houses, and electronic devices is a considerable field of research and has the potential to change the way we think of power.

Here are the five main areas of fuel cell research with their respective benefits and limitations:

  • Alkaline fuel cell: Used by NASA to power spacecraft from the beginning of the space program. Is very efficient, and uses a very high quality combination of Hydrogen and Oxygen to achieve this effect. Main limitation is that the cells are very fragile and not very tolerant of any sort of contamination. This makes it unlikely to see such fuel cells for average consumers. Potassium hydroxide is used as the electrolyte for this reaction. Hydroxyl ions (OH-) move from cathode to anode. Here, hydrogen bonds to form water. The extra electron is released and does work before returning to the cathode to form more OH- ions. This cell is up to 70 percent efficient.

  • Phosphoric-acid fuel cell: This fuel cell has potential backup generators or secondary generating plants for peak usage hours on power grids. This fuel cell requires a long warm up period as the cell operates at over 300 degrees F (150 C). This long warm-up makes it unsuitable for use in devices that need to be turned on and off frequently; cars, electronics, etc. This fuel cell is reliable and produces electricity on a similar efficiency rating as Alkaline Fuel Cells and is more tolerable to impurities. Phosphoric acid is the electrolyte used in this cell. A catalysts of platinum causes hydrogen to become hydrogen ions and migrate to the cathode. The electrons are forced to travel through the wires to migrate to the cathode portion of the cell. Once the electrons reach the cathode, the hydrogen and oxygen bond to form water. The water is then removed from the cell. When used without steam generators, efficiency of about 50 percent, increased to 80 percent when equipped with steam generators.

  • Solid oxide fuel cell: These fuel cells only operate once warmed up to 1,832 degrees F (1000 C). This limitation means that these cells can only be used in permanent locations with the necessary equipment to warm the cell up to operation temperature. Special materials are also needed to build the cells to withstand the temperatures within the system during operation. Though the high heat effects longevity and reliability of the system, the cells can be used to create steam from the excess heat produced, increasing the efficiency of the units. Zirconium oxide and calcium oxide are used to form crystal lattice structures for the electrolyte. At the high operating temperatures, oxygen moves through the lattice and become negatively charged. The hydrogen at the anode releases electrons to do work. The electrons then move to the cathode to join with oxygen completing the circuit. Efficiencies can range up to about 60 percent.

  • Molten carbonate fuel cell: These cells are perhaps the most likely to be used on a large scale to produce electricity and replace oil or coal fired plants. They operate at 1,112 degrees F (600 C), meaning they too can produce steam to be used by regular turbines. This double production of electricity combined with the lower cost of the unit, as exotic materials are not needed to withstand operating temperatures makes this fuel cell commercially viable. When operating temperature is reached the carbonate salts used as electrolytes melt and conduct carbonate ions from cathode to anode. At the anode hydrogen and oxygen combine to form water and release electrons. The electrons move through the circuit and return at the cathode. The electrons are used to form new CO3 ions and continue the process. Efficiency is about 60 percent without using the waste heat, 80 percent when steam generators are used as well.

  • Proton exchange membrane fuel cell: A very simple fuel cell, this unit operates at very low temperatures, 176 degrees F (80 C), and can accept any type of hydrogen and oxygen to power the unit. Can withstand movement and impurities, but is not as efficient when compared to other fuel cell technology. Using a membrane that allows only positive ions to pass through, the cell forces electrons to flow through wires to get to the hydrogen ions that move from anode to cathode. Most likely to be used in consumer products due to flexibility in fuel sources. A reformer is needed to turn fuels into hydrogen for the cell to use, and this reduces fuel cell efficiency. Efficiency reaches about 50 percent under the best conditions.

Bibliography

http://www.howstuffworks.com/fuel-cell.htm

http://fuelcells.si.edu/index.htm

The Zinc/Air fuel cell is unlike most fuel cell technologies, as it does not require a high-pressure or high-temperature operating environment. In addition, it does not require the use of fuel reformers.

The technology produces electrical energy by the same processes that occur in zinc/air batteries, but as a regenerative technology does not need to be disposed of after discharge, and can be refueled in a simple process. The zinc fuel is in the form of pellets 0.5 to 0.8 mm in diameter.

When all or part of the zinc fuel is transformed into zinc oxide, the cell is then refueled by removing the reaction product, and adding fresh pellets and electrolyte. The pellets are suspended in the electrolyte fluid, so the process is similar to any non-flammable fluid transfer process. Alternatively, the regeneration components can be packaged with the fuel cell to form a complete system that recharges automatically upon the application of external power. Round-cycle efficiency is approximately 50%.

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