Redox Electrochemistry

In a hydrogen­-oxygen fuel cell, combustion of hydrogen occurs to

  1. remove adsorbed oxygen from electrode surface
  2. produce high purity water
  3. generate heat
  4. create potential difference between the two electrodes


Direct conversion of chemical energy to electric energy can be made considerably more efficient (i.e. upto 75%) than the 40% maximum now obtainable through burning of fuel and using the heat to form steam for driving turbines. Furthermore, the water obtained as a byproduct may be used for drinking by the astronauts.

At anode: 2H2(g) + 4OH(aq)  → 4H2O(l) + 4e

At cathode: O2(g) + 2H2O(l) + 4e  → 4OH(aq)

2H2(g) + O2(g) →  2H2O(l)

The correct option is D.