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PAFC power plant in Alaska
source: http://www.wisconsindr.org/

Phosphoric Acid Fuel Cells (PAFC) were the first fuel cells to be released. This type was developed in the middle of the 1960’s, and the first ones were sold in the next decade. In comparison with other types of fuel cells it appeared to behave much more stably, and it delivered higher power at a relatively low price. In these cells the electrolyte was exclusively phosphorous acid (H₃PO₄). Since the ionic conductivity of phosphorous acid is small at a low temperature, therefore their operating temperature is rather high, sometimes exceeding 200°C. Its operation is similar to that of the Proton Exchange Membrane Fuel Cells. Therefore, the reactions on the cathode and the anode are the same as for PEMFCs.

Parameters:

• Type of electrolyte: undiluted liquid phosphorous acid
• Operational temperature: 150°C-220°C
• Electric efficiency: 50%-60%

Reactions:

• On the anode: 2H₂ => 4H⁺ + 4e^-
• On the cathode: O₂ + 4H⁺ + 4e^- => 2H₂O
• The complete reaction: 2H₂ + O₂ => 2H₂O

Advantages:

• The high operational temperature allows the efficient utilization of heat
• Not sensitive to carbon dioxide and carbon monoxide
• Long lifetime (phosphorous acid is low-volatile)
• Stability
• Simple construction

Disadvantages:

• Large size
• Requires platinum catalyst
• Hard starting (phosphorous acid is solid under 40°C)

Areas of use

• Energy supply of buildings
• Power plants
• Arms industry

Related links

1. Fuel Cell Basics
2. Wikipedia
3. NREL