(Max Bredig Award in Molten Salt & Ionic Liquid Chemistry) Molten Salts and Ionic Liquids: Where Have We Been and Where Are We Going? An Electrochemist’s Perspective

From the very beginnings of molten or fused salt chemistry in the early 19^th century with the preparation of alkali metals from their molten hydroxides by Sir Humphrey Davy, the formulation of the laws of electrolysis by Michael Faraday from experiments with molten lead halides, and the eventual development of the civilization-changing Hall-Héroult process for the large scale production of aluminum in 1886, there has always existed a common theme of electrochemical applications.  Molten salt electrolytes can be prepared from almost any stable salt, but the most commonly employed systems are based on alkali carbonates, halides, hydroxides, and nitrates and their mixtures.  These melts have found applications in batteries and fuel cells; the electrowinning, surface treatment, and heat treatment of metals; and even in the electrochemical processing of spent nuclear fuel.  Many are commonly employed at temperatures well over 1000 ^oC!

Latecomers to the field of molten salt chemistry include the class of materials known as “ionic liquids,” which are by agreement salts that melt below 100 ^oC and are usually, but not absolutely, based on organic cations and inorganic anions.  Although they can trace their origin to the first report of the room-temperature protic salt, ethylammonium nitrate, by Paul Walden in 1914, their novel properties and electrochemical applications were not really appreciated until the pioneering work of Frank H. Hurley and Thomas P. Wier, who electrodeposited aluminum from room-temperature mixtures of ethylpyridinium bromide and aluminum chloride (U.S. Patents 2,446,331; 2,446,349; and 2,446,350) in 1944.  In a sense, it is the work by these early pioneers from which everything else pertaining to ionic liquids has flowed, including the development of the ubiquitous dialkylimidazolium chloride salts and many other quaternary ammonium salts that form the backbones of the fascinating, highly-stable hydrophobic ionic liquids we use as electrochemical solvents today.

In this presentation, the award recipient will provide a brief historical perspective about the electrochemical applications of molten salts and their ionic liquid progeny.  He will also describe his work with previous Bredig Award recipients and with many other long-time collaborators and students in the field of molten salts and ionic liquids.