PHOSPHORIC ACID FUEL CELL(PAFC)

& HYDROGEN OXYGEN FUEL CELL

What is a fuel cell?

• A fuel cell is a device that generates electricity by a chemical reaction.

• Has two electrodes, one positive and one negative respectively the anode and cathode. The reactions that produce electricity take place at the electrodes.

• Has an electrolyte, which carries electrically charged particles from one electrode to the other

• And a catalyst, which speeds the reactions at the electrodes.

PHOSPHORIC ACID FUEL CELL• Electrolyte-Conc.Phosphoric acid• Electodes-Porous conducting material(commonly

nickel)• At negative electrode-Pure Hydrogen or Hydrogen

rich gas is supplied• At negative electrode-Oxygen or Air is supplied• Catalyst- Finely divided Platinum or Nickel/Silver• Operational temperature: 150°C-220°C• Electric efficiency: 50%-60%• EMF produced 1.23v @25 degree Celsius 1.15v @200 degree Celsius

WORKING DIAGRAM

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

HYDROGEN OXYGEN FUEL CELL

• Electrolyte-40% aqueous KOH• Electrodes-Porous conducting material(commonly

nickel)• At negative electrode-Pure Hydrogen or Hydrogen

rich gas is supplied• At negative electrode-Oxygen or Air is supplied• Catalyst- Finely divided Platinum or Nickel/Silver• Operational temperature: below 80 degree Celsius• Electric efficiency: 60-70%• EMF produced :1.1V

WORKING DIAGRAM

•On the anode: 2H2 + 4OH- => 4H2O + 4e-

•On the cathode: O2 + 2H2O + 4e- => 4OH-

•The complete reaction: 2H2 + O2 => 2H2O

REACTION

ADVANTAGES:•One of the most efficient cells•Low production costs due to the fact that different types of electrolytes can be used•Relatively low operational temperature•Quick start

DISADVANTAGES:•High sensitivity to carbon dioxide, carbon monoxide and methane, since these gases can react with the electrolyte and so reduce the efficiency of the cell. It feels best locked away from the outer world, where these gases cannot damage it•Pure hydrogen and oxygen are needed for its operation

AREAS OF USE:•Submarines•Ships•Arms industry