Q.What are 'fuel cells'? Write cathode and anode reaction in a fuel cell.

Fuel cells generate electricity by continuously oxidising a fuel gas at the anode and reducing oxygen at the cathode, over a KOH electrolyte.

A fuel cell is a galvanic (voltaic) cell in which the reactants — a fuel such as hydrogen, methane or methanol, and an oxidant such as oxygen or air — are fed in continuously from outside, so the cell keeps generating electrical energy as long as the supply lasts, without needing to be recharged like an ordinary battery. The $H_2$–$O_2$ fuel cell is the classic example: two porous carbon electrodes (impregnated with catalysts like Pt/Pd) are dipped in concentrated aqueous KOH; hydrogen gas is bubbled at the anode and oxygen gas at the cathode.

Anode (oxidation): $2H_2(g) + 4OH^-(aq) \rightarrow 4H_2O(l) + 4e^-$

Cathode (reduction): $O_2(g) + 2H_2O(l) + 4e^- \rightarrow 4OH^-(aq)$

Overall cell reaction: $2H_2(g) + O_2(g) \rightarrow 2H_2O(l)$

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