Question

Answer the following:

What are anode and cathode of H₂ - O₂ fuel cell? Name the electrolyte used in it. Write electrode reactions and net cell reaction taking place in the fuel cell.

Answer 1

1) The anode and cathode are porous carbon rods containing small amount of finely divided platinum metal that acts as a catalyst.

2) The electrolyte used is hot aqueous solution of KOH.

3) Working (Cell reactions):

i) Oxidation at anode (–):

At anode hydrogen gas is oxidized to H₂O

`2"H"_(2("g")) + 4"OH"_(("aq"))^(-) -> 4"H"_2"O"_(("l")) + 4"e"^(-)`        .....(1)

ii) Reduction at cathode (+):

The electrons released at anode travel, through external circuit to cathode. Here O₂ is reduced to OH^–.

`"O"_(2("g")) + 2"H"_2"O"_(("l")) + 4"e"^(-) -> 4"OH"_(("aq"))^(-)`      .....(2)

iii) Net cell reaction:

The overall cell reaction is the sum of electrode reactions (1) and (2).

`2"H"_(2("g")) + "O"_(2("g")) -> 2"H"_2"O"_(("l"))`

The overall cell reaction is combustion of H₂ to form liquid water. However, the fuel H₂ gas and the oxidant O₂ do not react directly. The chemical energy released during the formation of O-H bond is directly converted into electrical energy accompanying in above combustion reaction. The cell continues to operate as long as H₂ and O₂ gases are supplied to electrodes.