Fuel Cells

A fuel cell is an efficient electrochemical device that converts a fuel such as hydrogen into electricity and emits only water and heat. Unlike a combustion engine or steam turbine, a fuel cell is a solid state device that that creates electricity by passing the input fuel through the fuel cell and the electrons migrate between the anode and cathode, in the much the same way as a battery, to produce DC electricity.

Many types of fuel cells are in production or under development for a variety of applications such as cogeneration, transportation and even micro fuel cells to power portable consumer electronic devices.

Certain types of fuel cells are especially suited to cogeneration applications because they produce both a constant supply of electricity and thermal energy which can be used to power buildings and for their heating or cooling. Most fuel cells are fuelled by hydrogen which is easily extracted on site from a natural gas supply, or it can be extracted from water using electricity from a wind turbine or photovoltaic solar cell.

When fuelled by natural gas, a fuel cell emits 80% less carbon dioxide and green house gasses than conventional centralised power stations and is 100% free of carbon dioxide when acting as a battery to a wind or solar renewable energy technology.

Types of Fuel Cell

• Solid oxide fuel cell (SOFC)
  These fuel cells are best suited for large-scale stationary power generators that could provide electricity for factories or towns. This type of fuel cell operates at very high temperatures (between 700 and 1,000 degrees Celsius). This high temperature makes reliability a problem, because parts of the fuel cell can break down after cycling on and off repeatedly. However, solid oxide fuel cells are very stable when in continuous use. In fact, the SOFC has demonstrated the longest operating life of any fuel cell under certain operating conditions. The high temperature also has an advantage: the steam produced by the fuel cell can be channeled into turbines to generate more electricity. This process is called co-generation of heat and power (CHP) and it improves the overall efficiency of the system.
• Alkaline fuel cell (AFC)
  This is one of the oldest designs for fuel cells; the United States space program has used them since the 1960s. The AFC is very susceptible to contamination, so it requires pure hydrogen and oxygen. It is also very expensive, so this type of fuel cell is unlikely to be commercialized.
• Molten-carbonate fuel cell (MCFC)
  Like the SOFC, these fuel cells are also best suited for large stationary power generators. They operate at 600 degrees Celsius, so they can generate steam that can be used to generate more power. They have a lower operating temperature than solid oxide fuel cells, which means they don't need such exotic materials. This makes the design a little less expensive.
• Phosphoric-acid fuel cell (PAFC)
  The phosphoric-acid fuel cell has potential for use in small stationary power-generation systems. It operates at a higher temperature than polymer exchange membrane fuel cells, so it has a longer warm-up time. This makes it unsuitable for use in cars.
• Direct-methanol fuel cell (DMFC)
  Methanol fuel cells are comparable to a PEMFC in regards to operating temperature, but are not as efficient. Also, the DMFC requires a relatively large amount of platinum to act as a catalyst, which makes these fuel cells expensive.