Polymer Electrolyte Membrane Fuel Cell (PEMFC) or Solid Polymer Fuel Cell (SPFC)

Polymer Electrolyte Membrane Fuel Cell (PEMFC) or Solid Polymer Fuel Cell (SPFC) 

• The schematic diagram of a low temperature polymer electrolyte membrane fuel cell shown in Figure A. In this type of cell, the electrolyte is a solid polymer membrane of an organic material such as polystyrene sulfonic acid.

• This polymer is permeable to H⁺ ions to pass through it when it is saturated with water but it does not conduct electrons. Other properties include that this polymer has high resistance to dehydration and oxidation coupled with high ionic conductivity. The membrane is coated on its both sides with finely powdered platinum which acts as catalyst.
• The fuel used is, and oxidant as H₂. The electro-chemical reactions are :

At anode : H₂ = 2H⁺ + 2e

At cathode : 1/2 O₂ + 2H⁺ + 2e =  H₂O

Overall reaction is :  H₂ + 1/2O₂=  H₂O + Heat

Advantages of PEMFC are :

1. It can be started quickly.
2. Polymer membrane retains only limited quantity of water and rejects excess H₂O vapour produced in the cell.
3. It is comparatively cheap.
4. It has no corrosion problems due to use of polymer.
5. It has an ideal e.m.f. of 1.23V and actual e.m.f. of about 1V at 25°C.
6. It operates at low temperature of 40°C – 60°C.

Desirable properties of an ideal ion-exchange membrane :

1. Zero electronic conductivity.
2. Low permeability of fuel and oxidant.
3. High ionic conductivity.
4. High resistance to dehydration and hydrolysis.
5. Mechanical stability.