Magnesium, electrochemistry

D. Aurbach and A. Schechter, On Non-aqueous Magnesium Electrochemistry, in preparation (1998). 

Magnesium electrochemistry in molten salts media is especially important for the mass production of the pure metal. Magnesium is frequently produced and refined by electrolysis of high-temperature, molten eutectic mixtures of anhydrous MgCl2 with various salts, such as KC1, CaCl2 etc. High-temperature molten salts baths, with similar compositions, with the addition of borate are also studied for the production of MgB2. 

Hence, when reviewing important aspects of non-aqueous magnesium electrochemistry, it is important to consider the reversibility of Mg deposition processes, to map possible corrosion process of Mg electrodes, and to determine the anodic stability of electrolyte solutions in which Mg electrodes behave reversibly. In the following sections, we will briefly review conventional non-aqueous electrolyte solutions and the passivation of active metals in non-aqueous solutions, after which we will describe systematically the behavior of Mg electrodes in various types of conventional and non-conventional non-aqueous electrolyte solutions. Finally, we will review in brief another important aspect of non-aqueous magnesium electrochemistry, which is the electrochemical intercalation of Mg ions into inorganic hosts. 

Another important class of polar aprotic systems that can be relevant for magnesium electrochemistry is that of ionic liquids (ILs). Figure 13.4 presents formulae of relevant ionic liquids. This figure also includes tabulated physical properties of commonly used ILs in electrochemistry. The main important features of ILs are the possibility to obtain highly ionically conducting solutions with wide electrochemical windows, low... 

In certain IL systems, such as ethyl-methyl imidazolium-AICI4, Mg metal visibly dissolves. We tried to repeat the experiments described by Nuli et al. [50,51] but were unable to obtain any reversible behavior of Mg electrodes or reversible Mg deposition-dissolntion processes or noble metal electrodes in any of the IL systems described in Fig. 13.8. Hence, we have to conclude that most commonly used ILs, including those showing apparent high cathodic stability, are not suitable solvents for reversible Mg electrodes. Thereby, ILs cannot be considered as compatible/promising electrolyte solutions for non-aqueous magnesium electrochemistry. 

Sir Humphry Davy, 1778—1829. English chemist and physicist. One of the founders of electrochemistry. Inventor of die safety lamp for miners. He was the first to isolate potassium, sodium, calcium, barium, strontium, and magnesium. Davy in England and Gay-Lussac and Thenard in France, working independently, were die first to isolate boron. 

There are two major interests in nonaqueous electrochemistry of magnesium ... 

Nonaqueous solvents can form electrolyte solutions, using the appropriate electrolytes. The evaluation of nonaqueous solvents for electrochemical use is based on factors such as -> dielectric constant, -> dipole moment, - donor and acceptor number. Nonaqueous electrochemistry became an important subject in modern electrochemistry during the last three decades due to accelerated development in the field of Li and Li ion - batteries. Solutions based on ethers, esters, and alkyl carbonates with salts such as LiPF6, LiAsly, LiN(S02CF3)2, LiSOjCFs are apparently stable with lithium, its alloys, lithiated carbons, and lithiated transition metal oxides with red-ox activity up to 5 V (vs. Li/Li+). Thereby, they are widely used in Li and Li-ion batteries. Nonaqueous solvents (mostly ethers) are important in connection with other battery systems, such as magnesium batteries (see also -> nonaqueous electrochemistry). 

Modem electrochemistry is concerned not only with systems based on aqueous solutions but also with solvent-free systems. Indeed, it is in such systems that many important electrochemical processes are carried out, such as the production of metals (aluminum, sodium, and magnesium) and the development of high-energy-density batteries. 

The basket-handle and picket-fence porphyrins show dramatic effects not only during metallation and binding of small molecules but in their redox and coordination chemistry. Detailed studies on the electrochemistry of the iron complex have been made paralleling the earlier electrochemical studies on the free base, magnesium and zinc complexes of 192. and 201 ... 

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