Electrolysis of a molten salt uses electrical energy to force a non-spontaneous redox reaction. The molten ionic compound is decomposed as its cations are reduced at the cathode and its anions are oxidized at the anode.
This is SL and HL content within Reactivity 3.2, electron transfer reactions.
The Mechanism
When an ionic salt melts, its lattice breaks apart and the ions become mobile. These ions carry charge through the liquid: cations move toward the negative electrode, while anions move toward the positive electrode.
A direct-current power supply pushes electrons toward the cathode, making it negative, and removes electrons from the anode, making it positive. Reduction occurs at the cathode because cations gain electrons; oxidation occurs at the anode because anions lose electrons.
For molten sodium chloride, the mobile ions are and :