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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.
Solution
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.
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