Battery or cell converts chemical energy of the redox reaction to electrical energy. In fuel cell (a galvanic cell), the chemical energy of combustion of fuels like H2 , ethanol, etc. are directly converted to electrical energy. In a fuel cell, H2 and O2 react to produce electricity, where H2 gas is oxidised at anode and oxygen is reduced at cathode and the reactions involved are
Anode reaction : H₂ + 2OH– -> 2H₂O + 2e–

Cathode reaction : O₂+ 2H₂O + 4e– -> 4OH–

67.2 L of H₂ at STP reacts in 15 minutes.