Q.Draw labelled diagram of $H_2-O_2$ fuel cell. Write two applications of fuel cell.

$H_2$ and $O_2$ are fed to porous catalytic electrodes in alkaline electrolyte; their combination generates electric current directly, with water as the only product.

$H_2-O_2$ fuel cell (structure): two porous carbon electrodes, each impregnated with a catalyst (finely divided platinum or palladium), are immersed in a concentrated aqueous KOH (or NaOH) electrolyte. Hydrogen gas is continuously bubbled through the anode compartment, and oxygen gas through the cathode compartment; the two electrodes are connected externally through a load, and the electrolyte permits ion flow between them.

Electrode reactions:

• Anode (oxidation): $2H_2 + 4OH^- \rightarrow 4H_2O + 4e^-$
• Cathode (reduction): $O_2 + 2H_2O + 4e^- \rightarrow 4OH^-$
• Overall: $2H_2 + O_2 \rightarrow 2H_2O$ …