text: Aluminium is produced by electrolytic reduction of aluminium oxide dissolved in molten cryolite.
  At the same time the carbon electrode is oxidised, initially to carbon monoxide
  Although the formation of carbon monoxide (CO) is thermodynamically favoured at the reaction temperature, the presence of considerable overvoltage (difference between reversible and polarization potentials) changes the thermodynamic equilibrium and a mixture of CO and  is produced. Thus the idealised overall reactions may be written as
  By increasing the current density up to 1 A/cm, the proportion of  increases and carbon consumption decreases.
  As three electrons are needed to produce each atom of aluminium, the process consumes a large amount of electricity. For this reason aluminium smelters are sited close to sources of inexpensive electricity, such as hydroelectric.