Galvanic cells which use energy for combustion of fuels like H2,CH4,CH3OH etc. as the source to produce electrical energy are called fuel cells. Fuel cell uses the reaction of H2 and O2 in gaseous state to form water. At anode, hydrogen is oxidised to H2O (i) 2H2───▸4H++4e− (ii) 4H++4OH−───▸4H2O At cathode, oxygen is reduced to OH⊖ ions O2(g)+2H2O(l)+4e−───▸