Module 5 : Electrochemistry
Lecture 23 : Batteries and Fuel Cells
 
The combustion (oxidation) reaction
2 H2 ( g ) + O2 ( g ) = 2 H2 O, can be made to occur in a galvanic cell of the type (Fig. 23.3)
Inert electrode H2 ( g) | H+ | O2 ( g) Inert electrode
 
Anode: 2H2 + 4H2O = 4 H3O+ + 4e (E 0 = 0)
Cathode: O2+ 4H 3O+ + 4e = 6 H2O (E 0 = 1.23 V)
 

In the H2- O2 fuel cell, the electrodes are Ti coated with porous Pt, and a water-soaked caution exchange resin in the acid form is used as the electrolyte. If the pressure of the gases are 1 atm, and water in the resin is pure, the EMF of this cell should be + 1.23 V, corresponding to the cathode reaction O2+ 4 H 3O+ + 4e = 6 H2O.
This is because the potential of the hydrogen electrode under these conditions is zero. In practice, the emf is about 0.8 to 1.0 V.
 

The only product discharged by the cell is water. The electrolyte in a H2 - O2 fuel cell may also be alkaline.

The electrode reactions in this case are
O2+ 2 H 2 O + 4e- = 4 OH - ; E 0 = + 0.40 V
 

Figure 23.3 : Schematic representation of a H2 - O2 fuel cell using H30+ as electrolyte
 

1] Ti electrodes coated with porous Pt, 2] Fuel (H 2) inlet, 3] Oxidiser (O2) inlet, 4] Caution exchange membrane in acid form (source of H+).

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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