Phosphoric acid fuel cell

File:Proton Exchange Fuel Cell Diagram.svg

Diagram of a phosphoric acid fuel cell

Phosphoric acid fuel cells (PAFC) are a type of fuel cell that uses liquid phosphoric acid as an electrolyte. They were the first fuel cells to be commercialized. Developed in the mid-1960s and field-tested since the 1970s, they have improved significantly in stability, performance, and cost. Such characteristics have made the PAFC a good candidate for early stationary applications.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Design

Electrolyte is highly concentrated or pure liquid phosphoric acid (H₃PO₄) saturated in a silicon carbide (SiC) matrix. Operating range is about 150 to 210 °C. The electrodes are made of carbon paper coated with a finely dispersed platinum catalyst.

Electrode reactions

Anode reaction: 2H₂(g) → 4H⁺ + 4e

Cathode reaction: O₂(g) + 4H⁺ + 4e‾ → 2H₂O

Overall cell reaction: 2 H₂ + O₂ → 2H₂O

Advantages and disadvantages

At an operating range of 150 to 200 °C, the expelled water can be converted to steam for air and water heating (combined heat and power). This potentially allows efficiency increases of up to 70%.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> PAFCs are CO₂-tolerant and can tolerate a CO concentration of about 1.5%, which broadens the choice of fuels they can use. If gasoline is used, the sulfur must be removed.<ref name="FCorg">Fuel Cells 2000 : Fuel Cell Basics : Types Template:Webarchive.</ref> At lower temperatures phosphoric acid is a poor ionic conductor, and CO poisoning of the platinum electro-catalyst in the anode becomes severe.<ref name="FuelcellHandbook">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> However, they are much less sensitive to CO than proton-exchange membrane fuel cells (PEMFC) and alkaline fuel cells (AFC).

Disadvantages include rather low power density and chemically aggressive electrolyte.Template:Clarify

Applications

File:PureCell System 400 CEP.jpg

PureCell System 400 CEP

PAFC have been used for stationary power generators with output in the 100 kW to 400 kW range and are also finding application in large vehicles such as buses.<ref name="FCToday">Fuel Cell Today – Home Page.</ref>

Major manufacturers of PAFC technology include Doosan Fuel Cell America Inc.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> (formerly ClearEdge Power & UTC Power<ref>ClearEdge Power – Media Room.</ref>) and Fuji Electric.

India's DRDO has developed PAFC based air-independent propulsion for integration into their Template:Sclasss.<ref>Template:Cite news</ref><ref>Template:Cite news</ref>

See also

• Glossary of fuel cell terms

External links

• National Pollutant Inventory - Phosphoric acid fact sheet
• UTC Power Official Site
• Photo Gallery of Fuel Cells Being Used Today
• Cox Communications Installs Fuel Cells in California Template:Webarchive
• D.O.E. -PAFC
• Fuel Cell Basics
• Alternative Energy Magazine Template:Webarchive
• Supermarket Benefits From 400kW Fuel Cell
• Stationary Fuel Cells at Retail and Grocery Sites