FUEL CELLS Chapter 7

Types of Fuel Cells Fuel CellOperating Conditions Alkaline FC (AFC)Operates at room temp. to 80 0 C Apollo fuel cell Proton Exchange Membrane FC (PEMFC) Operates best at C Hydrogen fuel Originally developed by GE for space Phosphoric Acid FC (PAFC)Operates best at ~200 0 C Hydrogen fuel Stationary energy storage device Molten Carbonate FC (MCFC)Operates best at C Nickel catalysts, ceramic separator membrane Hydrocarbon fuels reformed in situ Solid Oxide FC (SOFC)Operates at C Conducting ceramic oxide electrodes Hydrocarbon fuels reformed in situ Direct Methanol Fuel Cell (DMFC) Operates best at C Methanol Fuel For portable electronic devices

Chemistry of a Fuel Cell  Anode : 2H 2  4H e -  Cathode : O 2 + 4H e -  2H 2 O  Net reaction: 2H 2 + O 2  2H 2 O

Proton Exchange membrane / Polymer Electrolyte Membrane Fuel Cells (PEMFCs)

 Electrolyte: Use a solid polymer (Poly perfluorosulfonic acid polymer / Naflon).  Electrodes used: Porous carbon electrodes containing a Pt catalyst.  Cell output: 50 – 250kW.  Chemical Reaction Involved: Anode : 2H 2  4H + + 4e - Cathode : O 2 + 4H + + 4e -  2H 2 O Net reaction: 2H 2 + O 2  2H 2 O

PEMFC

Advantages of PEMFCs  Operating Temperature 90 o C lower than other fuel cells.  High power density, low weight and volume  Because of low operating temperature results in less wear and better durability.  Quick start up properties use for automobile applications  No corrosive fluids

Disadvantages of PEMFCs  Expensive platinum as a catalyst extremely sensitive to CO poisoning.  Hydrogen storage is problem. Applications of PEMFCs  In Automobiles applications for light duty vehicles.  Building rechargeable batteries.

Phosphoric acid Fuel Cell (PAFC)

Phosphoric Acid Fuel cell  World first commercially available fuel cell produced by UTC  First generation of modern fuel cell.  Electrolyte: Liquid Phosphoric acid retained on a silicon carbide material.  Operating temperature: o C.  Catalyst: platinum  Electrical efficiency of 40%

Advantages :  Using impure hydrogen as fuel.  85% of the steam can be used for cogeneration of heat and electricity.  Tolerate up to 1.5% poisoning of CO concentration.

Disadvantages:  At low temperature, phosphoric acid is a poor ionic conductor.  Less efficient 37-42%.  Large size and weight  uses expensive platinum as catalyst  Low power and current  Existing PAFC’s have outputs of 200kW and 1MW are being tested

Applications  Use for stationary power generation and in heavy and large vehicles.  Used in hospitals, nursing homes, an air port terminals, waste treatment plant and for all commercial purposes.