Phosphoric acid fuel cells (PAFC) are a type of

fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen fuel, hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most bat ...

that uses liquid

phosphoric acid Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solutio ...

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.

Design

Electrolyte is highly concentrated or pure liquid phosphoric acid (H₃PO₄) saturated in a

silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal ...

(SiC) matrix. Operating range is about 150 to 210 °C. The

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials ...

s are made of

carbon paper Carbon paper (originally carbonic paper) consists of sheets of paper which create one or more copies simultaneously with the creation of an original document when inscribed by a typewriter or ballpoint pen. History In 1801, Pellegrino Tur ...

coated with a finely dispersed

platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Pla ...

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

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 Cogeneration or combined heat and power (CHP) is the use of a heat engine or power station to generate electricity and useful heat at the same time. Cogeneration is a more efficient use of fuel or heat, because otherwise- wasted heat from elec ...

). This potentially allows efficiency increases of up to 70%. 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.Fuel Cells 2000 : Fuel Cell Basics : Types
At lower temperatures phosphoric acid is a poor ionic conductor, and CO poisoning of the platinum electro-catalyst in the anode becomes severe. However, they are much less sensitive to CO than proton-exchange membrane fuel cells (PEMFC) and

alkaline fuel cell The alkaline fuel cell (AFC), also known as the Bacon fuel cell after its British inventor, Francis Thomas Bacon, is one of the most developed fuel cell technologies. Alkaline fuel cells consume hydrogen and pure oxygen, to produce potable wate ...

s (AFC). Disadvantages include rather low power density and chemically aggressive electrolyte.

Applications

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.Fuel Cell Today – Home Page
Major manufacturers of PAFC technology include Doosan Fuel Cell America Inc. (formerly ClearEdge Power & UTC Power) and Fuji Electric. India's DRDO has developed PAFC based air-independent propulsion for integration into their s.

References

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

Fuel Cell Basics

Alternative Energy Magazine

Supermarket Benefits From 400kW Fuel Cell

Stationary Fuel Cells at Retail and Grocery Sites
{{Fuel cells Fuel cells ko:연료전지#인산형 연료전지 (Phosphoric Acid Fuel Cell, PAFC) ja:燃料電池#りん酸形燃料電池 (PAFC)