Galvanic cells that are designed to convert
the energy of combustion of fuels like hydrogen, methane, methanol, etc. directly into electrical energy are called fuel cells

The electrode
reactions are given below:
Cathode: O2(g) + 2H₂O(l) + 4e^- -->4OH^-(aq)
Anode: 2H₂ (g) + 4OH^-(aq) ---> 4H₂O(l) + 4e^-

Overall reaction being:
2H₂(g) + O₂(g) ---> 2 H₂O(l )

Kohlrausch examined Ëm° values for a number of strong electrolytes and observed certain regularities. He noted that the difference in Ëm° of the electrolytes NaX and KX for any X is nearly constant. For example
at 298 K:

Ëm°(KCl) – Ëm° (NaCl)= Ëm°(KBr) – Ëm°(NaBr)
= Ëm°(KI) – Ëm° (NaI) ≃ 23.4 S cm2 mol–1

and similarly it was found that
Ëm°(NaBr)– Ëm°(NaCl)= Ëm°(KBr) – Ëm°(KCl) ≃ 1.8 S cm2 mol–1

On the basis of the above observations he enunciated Kohlrausch
law of independent migration of ions