Focus

Types of fuel cells

Different fuel cell designs use different materials, but the basic premise outlined above is the same.

Polymer Electrolyte Fuel Cells (PEFC) accept hydrogen as a fuel and operate at low temperatures. A subset of PEFC’s are Direct Methanol Fuel Cells (DMFC) which use methanol instead of hydrogen as a fuel, which is easier to transport.

Solid Oxide Fuel Cells (SOFC) and Molten Carbonate Fuel Cells (MCFC) operate at high temperatures, and the heat can internally reform almost any hydrocarbon fuel into hydrogen and carbon dioxide. The difference between them is their electrolyte, SOFC uses a ceramic compound and MCFC uses a molten carbonate held in a ceramic matrix.

The high power density and low operating temperature of PEFC lends itself to transport applications. The high temperatures (~900°C) of SOFC and MCFC means they are suited to co-generation stationary power, as waste heat can be used to run a turbine.

Fuel cells can also operate in “reverse”; using electricity to create hydrogen and oxygen from water.

Fuel Cell Type

Common
Electrolyte

Operating Temperature

System Output

Efficiency

Applications

Advantages

Disadvantages

Polymer Electrolyte Membrane (PEM)*

Solid organic polymer poly-perfluorosulfonic acid

50 - 100°C
122 - 212°F

<1kW – 250kW

50-60% electric

• Back-up power
• Portable power
• Small distributed generation
• Transportation

• Solid electrolyte reduces corrosion & electrolyte management problems
• Low temperature
• Quick start-up

• Requires expensive catalysts
• High sensitivity to fuel impurities
• Low temperature waste heat

Molten Carbonate (MCFC)

Liquid solution of lithium, sodium, and/or potassium carbonates, soaked in a matrix

600 - 700°C
1112 - 1292°F

<1kW – 1MW
(250kW module typical)

85% overall with CHP
(60% electric)

• Electric utility
• Large distributed generation

• High efficiency
• Fuel flexibility
• Can use a variety of catalysts
• Suitable for CHP

• High temperature speeds corrosion and breakdown of cell components
• Complex electrolyte management
• Slow start-up

Solid Oxide (SOFC)

Solid zirconium oxide to which a small amount of yttira is added

650 - 1000°C
1202 - 1832°F

5kW – 3MW

85% overall with CHP
(60% electric)

• Auxiliary power
• Electric utility
• Large distributed generation

• High efficiency
• Fuel flexibility
• Can use a variety of catalysts
• Solid electrolyte reduces electrolyte management problems
• Suitable for CHP

• High temperature enhances corrosion and breakdown of cell components
• Slow start-up

*Direct Methanol Fuel Cells (DMFC) are a subset of PEM typically used for small portable power applications with a size range of about a subwatt to 100W and operating at 60 - 90°C.