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 solution, ...

as an

electrolyte An electrolyte is a substance that conducts electricity through the movement of ions, but not through the movement of electrons. This includes most soluble Salt (chemistry), salts, acids, and Base (chemistry), bases, dissolved in a polar solven ...

. 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 wide bandgap semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder a ...

(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 a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...

s are made of carbon paper coated with a finely dispersed

platinum Platinum is a chemical element; it has Symbol (chemistry), symbol Pt and atomic number 78. It is a density, dense, malleable, ductility, ductile, highly unreactive, precious metal, precious, silverish-white transition metal. Its name origina ...

catalyst Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...

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 Efficiency is the often measurable ability to avoid making mistakes or wasting materials, energy, efforts, money, and time while performing a task. In a more general sense, it is the ability to do things well, successfully, and without waste. ...

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 cells (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 Air-independent propulsion (AIP), or air-independent power, is any marine propulsion technology that allows a non-nuclear submarine to operate without access to atmospheric oxygen (by surfacing or using a snorkel). AIP can augment or replace th ...

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)