Give an example of a fuel cell and write the cathode and anode reactions for it. 

Ans:

Fuel cells :Galvanic cells that are designed to convert the chemical energy from combustion of fuels like hydrogen, methane, methanol directly into electrical energy are called fuel cells. The efficiency of fuel cell is higher than that of galvanic cell, e.g. hydrogen-oxygen fuel cell, in which hydrogen and oxygen are bubbled through porous carbon electrodes into conc. KOH solution. Finely divided Pt or Pd metals are incorporated into the electrodes for increasing the rate of electrode reactions.

At cathode

$O_2(g) \, + \, 2H_2O(l) \, + \, 4e^{-} \rightarrow 4OH^-(aq) $

At anode

$ 2H_2(g) \, + \, 4OH^-(aq) \rightarrow 4H_2O(l) \, + \, 4e^{-} $

Overall reaction

$ 2H_2(g) \, + \, O_2 (g) \rightarrow 2H_2O(l) $