Electrochemistry in Molten Salts

A noticeable part of the important electrochemical processes proceeds at high temperatures using molten salt electrolytes. Electrochemistry of molten salts started at the beginning of the nineteenth century, when H. Davy extracted potassium and sodium from molten hydroxides by electrolysis in 1807. At the end of the nineteenth century C. M. Hall and P. L. T. Héroult invented the electrolytic route to aluminium production, and this led to the establishment of the largest industry of metal extraction from molten salts. Compared to aqueous solutions and organic electrolytes, the advantages of molten salts are the following:
1. The electrical conductivity is higher, i.e. about an order of magnitude higher than that of aqueous solutions and several orders higher than that of organic electrolytes.
2. The electrode reactions are faster at high temperatures.
3. The absence of water in the molten salt and therefore no hydrogen reduction. As a result metals with more negative potentials than hydrogen can be reduced.
Electrolytic production of metals from molten salts, with the Hall-Héroult process as the most important industrial application, is currently a major part of modern electrochemistry. In 1995 for example, the total world production was about 6.3 thousand metric tons of lithium, 339 thousand metric tons of magnesium, and 19.4 million metric tons of aluminium.
It is clear that in order to use and to develope the high-temperature electrochemical technologies the knowledge in modern electrochemistry of molten salts is important.
It was shown in the BRITE/Euram II Project (Contract no. BRE2.CT93.0447) that electrochemical investigation of the molten salt catalytic media can help to understand the mechanism of catalytic reaction.