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Fuel Cells

Here are two examples of proton-exchange-membrane fuel cells. They were designed to power buses.
Photo credit: Ballard Power Systems and DOE/NREL

Read a related article: Why Fuel Cells?

The first fuel cell was build about 150 years ago in England. More recently, fuel cell technology has been used as an efficient and lightweight energy source for space exploration. Fuel cells were carried aboard the Gemini and Apollo spacecraft and also aboard NASA's space shuttles.

Over the next few years, technological advances and cost reductions will likely lead to widespread use of fuel cells in a number of different applications. Fuel cells may someday be as common in residential households as refrigerators or dishwashers are today, producing clean and reliable electricity. In addition, it is highly likely that a new generation of clean automobiles using electric-drive motors will rely on fuel cells as their source of power. One-day families may buy cars that also serve as a small power plant, supplying energy and heat to their homes.

How a Fuel Cell Works

A fuel cell is a device that converts hydrogen and oxygen into electricity. Fuel cells are similar to batteries in their design, yet they do not run down or need recharging. Like a battery, fuel cells have electrodes, an electrolyte, and positive and negative terminals. An electrode is a conductor through which an electric current enters or leaves a medium, such as an electrolyte. Electrolytes are non-metallic conductors, which come in many different forms that allow a current to be carried by the movement of protons. However, electrons cannot move through electrolytes. Oxygen passes over one electrode (cathode) and hydrogen over the other (anode), generating electricity, water, and heat. The way in which this happens is that, 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 to react with oxygen creating water. The electrons are unable to pass through the electrolyte and must travel around it; thus creating direct current electricity that can be utilized before they return to the cathode. Individual fuel cells are assembled in stacks to provide the required power output. Fuel cells have no moving parts and produce little noise.

The first generation of commercially available fuel cells will rely on fossil fuels, such as natural gas and propane, as a source of hydrogen. These fuel cell systems must include a fuel reformer to extract the hydrogen from the fuel.

Fuel cells will offer greater environmental benefits when it becomes economical to extract pure hydrogen from water. Pure hydrogen can be produced through water electrolysis (splitting H20 into separate oxygen and hydrogen molecules) using electricity generated from renewable energy sources. This hydrogen could be used directly in fuel cells to generate electricity, thus completely eliminating the use of fossil fuels. The combination of a fuel cell using hydrogen with electricity generated from clean, renewable energy sources, such as solar or wind, would create a truly sustainable energy system. But before this vision can become a reality, many technological and cost barriers need to be overcome.

Fuel Cell Types

Fuel cells can be made from a variety of different materials. In general, fuel cell technology differs in terms of what type of electrolyte they contain.

  • The most commercially developed type of fuel cell is made from phosphoric acid. This type of fuel cell is most appropriate for larger scale applications. In fact, they are currently in use in hospitals, nursing homes, and other locations where power quality and reliability are critical.
  • Phosphoric acid fuel cells achieve very high conversion efficiencies (40%). Efficiencies are even higher when the waste heat is used for heating water or living spaces.
  • Another type of fuel cell contains a proton exchange membrane, in which a thin plastic membrane that looks like plastic wrap is used as the electrolyte. These fuel cells operate at low temperatures and have high power density, making them particularly attractive for transportation applications.
  • Alkaline fuel cells have been NASA's choice as a source of power for space exploration. These fuel cells use alkaline potassium hydroxide as the electrolyte. Although they are still very costly, several companies are looking at ways to cut costs and improve operating flexibility.
  • Solid oxide is another very promising fuel cell technology. A hard ceramic material is used instead of a liquid electrolyte. This fuel cell technology is best suited for large-scale power production applications.

Although there are other fuel cell technologies being developed, those described above represent the most promising, near-term fuel cell types.

Economics and Future Prospects

Fuel cell technology offers the potential to revolutionize electricity generation. This technology is well suited for ushering in a new, decentralized energy production and delivery system. Recent studies suggest that a decentralized energy system (also known as a "distributed" system) would improve overall efficiency through: 1.) reduced losses over power lines since electricity would no longer need to travel hundreds of miles from where it is produced to where it is used, and 2.) reduced investments in the transmission and distribution infrastructure. Furthermore, technologies, such as fuel cells, suited for distributed applications, generally produce less harmful pollution than the large central-station power plants used today.

A number of companies are actively developing fuel cell technology for commercial applications. Fuel cells can serve a number of niche markets from on-site generation to transportation. In addition to the size and performance of fuel cells, their cost will determine the applications and locations that make economic sense in the near term. One company currently markets fuel cells that use natural gas as a fuel for $3,000/kW. At this price, fuel cells only make sense in certain niche markets where electricity prices are very high and natural gas prices are very low. A recent study suggests that fuel cells with a $1,500/kW price would achieve market penetration nationwide in a number of different applications. One company claims that it will have a fuel cell ready for residential markets within one year that will generate electricity at a cost that is competitive with power purchased from the electric grid in certain regions. Given the high cost of electricity in the Northeast, fuel cells will likely be an attractive option for on-site power production. It is therefore likely that fuel cell technology will be widely available for commercial applications within the next several years.

Environmental Issues

Because fuel cells convert the fuel to electricity through an electrochemical process rather than a combustion process typical of most power plants, the emissions are much cleaner. Compared to burning fossil fuels like coal and oil, which produces emissions of sulfur dioxide, nitrogen oxide, and carbon dioxide, the electrochemical process used in fuel cells only has carbon dioxide and water as byproducts. The low emissions from fuel cells make them an environmentally preferred form of power production. However, it should be emphasized that the first generation of fuel cells will likely operate on natural gas or propane, which are finite fossil fuels whose extraction from the ground and delivery produce negative environmental impacts. In the future, fuel cells will run on gas derived from biomass (plant matter) or pure hydrogen extracted from water using wind or solar energy, thus playing a key role in ushering in a sustainable energy future.

For Further Information

Visit the following web sites:

Northeast Sustainable Energy Association
50 Miles Street
Greenfield, MA 01301
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