In the electrometallurgy of aluminium, a fused mixture of purified alumina (Al₂O₃), cryolite (Na₃AlF₆) and fluorspar (CaF₂) is electrolysed. In this electrolysis, graphite is used as the anode and graphite-lined iron is used as the cathode. During the electrolysis, Al is liberated at the cathode, while CO and CO₂ are liberated at the anode, according to the following equation.

Cathode: Al³⁺_(melt) + 3e^- → Al(l)

Anode: C_(s) + O^2-(melt) → CO_(g) + 2e^-

C_(s) + 2O^2-_(melt) → CO_2(g) + 4e-

If a metal is used instead of graphite as the anode, then O₂ will be liberated. This will not only oxidise the metal of the electrode, but also convert some of the Al liberated at the cathode back into Al₂O₃. Hence, graphite is used for preventing the formation of O₂ at the anode. Moreover, graphite is cheaper than other metals.