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Fuel Cell Types

Fuel cells are classified by their electrolyte, which can be in solid or liquid. There are many promising varieties of fuel cells. The main types in development in Canada are the proton exchange membrane, direct methanol, and solid oxide.

Proton Exchange Membrane

Science: An area of Canadian expertise, the Proton Exchange Membrane Fuel Cell (PEMFC) operates at a relatively low temperature, which means it starts and warms up quickly and does not require thermal insulation. The electrolyte is typically a thin polymeric membrane, and platinum is a typical catalyst in this kind of fuel cell.

Applications: Outputs range from 50 milliwatts to 250 kW. These fuel cells are currently the leading technology in transportation applications, and are also being used in some smaller stationary applications, micro and compact portable applications.

Direct Methanol

Science: The Direct Methanol Fuel Cell (DMFC) is a specific type of Proton Exchange Membrane Fuel Cell (PEMFC) that electrochemically converts methanol and oxygen to carbon dioxide and water to produce electricity and heat. The process of converting methanol is not as simple as that of converting hydrogen. Consequently, the power density of a DMFC is less than that of a PEMFC.

Applications: Outputs range from 1milliwatt to 25 kW. Applications are typically small devices such as lawn mowers, laptops and other consumer electronics.

Solid Oxide

Science: Solid Oxide Fuel Cells (SOFCs) use a ceramic electrolyte coated with specialized porous electrode materials, and may use nickel-based compounds as a catalyst. The advantages of SOFCs are high efficiency, high-grade heat and the potential to use hydrocarbon fuels directly without an external reformer. This fuel cell's high operating temperature (650 to 1000 °C ) enables it to extract hydrogen from natural gas through internal reforming - a process still at an early stage in development. At high current densities, some external reforming is also required. Otherwise the fuel cell stack cools itself by using heat produced during the reforming reaction.

Applications: With outputs ranging from 1 to 250 kW, these fuel cells can be used in stationary power systems and auxiliary power units of cars. The SOFC's high operating temperature makes it possible to use by-product heat for localized space heating or even steam turbine operation, which recovers some of the heat as additional electricity. Energy efficiency levels in the 70 to 80 % range are possible in a combined fuel cell/steam turbine machine.

Phosphoric Acid

Science: As the name suggests, Phosphoric Acid Fuel Cells (PAFCs) use phosphoric acid as the electrolyte. PAFCs operate at about 150 to 200°C and average 40 to 50 % efficiency. Efficiency can rise to about 80 % if the waste heat is reused in a cogeneration system.

Applications: Typical outputs are in the 250 kW range, making PAFCs ideal for small-scale stationary power systems. A 200 kW PAFC stationary cogeneration system was the first commercial fuel cell product.

Alkaline

Science: One of the oldest technologies, the Alkaline Fuel Cell AFC uses a water-based solution of potassium hydroxide as its electrolyte. The concentration can be varied with the fuel cell operating temperature. Most AFCs operate at temperatures between 100 and 250°C, but newer designs operate at 23°C to 80°C. The electrolyte used in most AFCs are non-freezing, allowing them to start quickly and operate at sub-zero freezing conditions.

Applications: Outputs range from 300 watts to 20 kW. Both NASA and the Russian space program have chosen AFCs to provide electricity, heat and pure water for all manned spacecraft. As an alternative low temperature technology, AFCs are seen as suitable for a wide range of stationary, portable and mobile applications for example golf carts, fork lifts and off-road vehicles are common applications.

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