Acidity of HCl in Neutral Buffered Chloroaluminate Molten Salts

King, Dawn; Mantz, Robert A.; Osteryoung, R. A.

doi:10.1021/ja961935b

Cited by 29 publications

(13 citation statements)

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“…Such means have been studied by different authors. [25][26][27][28][29] The use of insoluble solid CaCl 2 and MgCl 2 described by Koronaios and Osteryoung, 25 is a leading example. The control mechanism depends on the fact that excess Cl − activity is pre-empted by formation of the soluble MgCl 4 2− anion.…”

Section: In Developing Lialcl 4 -[Emi][alclmentioning

confidence: 99%

Approaches to, and Problems with, Ionic Liquid Electrolytes for Alkali Metal Electrochemical Devices: The Case of Low-Melting Chloroaluminate Binary Solutions

Tucker

Angell

2014

J. Electrochem. Soc.

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Despite many attempts to use ionic liquid media with dissolved lithium salts as the electrolyte component of electrochemical cells, there has been only limited success. Despite its small size, Li + seems to be the slowest species in the electrolyte, so the cells polarize. As sodium batteries gain attention, the needed Na + -containing ionic liquid electrolytes are likely to encounter similar, but more serious, kinetic problems. Here we first review past attempts to use, as an alternative, inorganic salts and quasi-salts of high conductivity, where conductivity increases with alkali content. Then we provide a detailed study of one organic cation system which confirms and extends earlier work by the Wilkes laboratory that showed how the opposite trend applied for mixtures of NaAlCl 4 with the ionic liquid ethylmethylimidazolium tetrachloroaluminate [EMI] [AlCl 4 ]. In the present work the depression of conductivity for the Na + case is fully characterized and is discussed in terms of a 1983 coulomb field alkali trapping concept for low-melting mixtures. This itself is an adaptation of earlier molten salt electrostatic and ionic polarizability models. The apparent exceptionalism of lithium salts in inorganic quasi-ionic liquid solutions is reviewed and possible ways of sidestepping the identified problems for sodium ion conductors are considered.There are many reasons for seeking liquid electrolytes that are free of molecular solvents for electrochemical applications. A leading one is the great reduction in fire hazard that such electrolytes usually offer. Another is the possibility of ionic conductivities competitive with those of the best salt-in-molecular solvent electrolytes. Wilkes and coworkers 1,2 had long ago (1984) shown that ionic liquids based on the ethylmethylimidazolium (EMI) cation, with tetrachloroaluminate anions, had conductivities as high as 22 mS/cm at 25 • C and 81 mS/cm at 100 • C These were a few% higher than the values reported some years earlier 3 for the α-picolinium tetrachloroaluminates (61 mS/cm at 100 • C) and had the advantage of remaining liquid to ambient temperatures. Both exceeded the conductivities of the "standard" lithium cell electrolyte, (LiPF 6 in the mixed cyclic-acyclic carbonate molecular solvents), 12 mS/cm at 25 • C for EC-DMC, 1:1. 4 Somewhat smaller values (9.1 mS/cm) can now be obtained with air and water-stable ethylmethylimidazolium bis-triflamideor EMINTf 2 ) according to Pan et al., 5 who confirm the earlier values of Tokuda et al. 6 and Widegren et al. 7 Slightly higher values (11 mS/cm) have recently been reported for [EMI + ][BF 2 (TFA) 2− ] by Gores and coworkers in a wide-ranging and precise study of fluoroborate-based anion systems. 8 Kim et al. 9 have since found that solutions of LiNTf 2 in EMINTf 2 may have conductivities only slightly smaller than those of the EMINTf 2 demonstrating that the pessimism concerning ion trapping of lithium in mixtures of lithium salts with ionic liquids expressed by Cooper and one of us, on the basis of early (1983) LiX-IL...

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Section: In Developing Lialcl 4 -[Emi][alclmentioning

confidence: 99%

Approaches to, and Problems with, Ionic Liquid Electrolytes for Alkali Metal Electrochemical Devices: The Case of Low-Melting Chloroaluminate Binary Solutions

Tucker

Angell

2014

J. Electrochem. Soc.

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“…King et al have measured the acidity of HCl in various neutral buffered melts, using arenes as weak indicator bases. Mantz et al have measured the Gutmann acceptor numbers of the neutral buffered melts themselves.…”

Section: Introductionmentioning

confidence: 99%

Acidity of Neutral Buffered 1-Ethyl-3-methylimidazolium Chloride−AlCl₃ Ambient-Temperature Molten Salts

1998

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A series of studies on the acidity of AlCl 3 -1-ethyl-3-methylimidazolium chloride (EMIC) melts buffered with alkali metal chlorides were carried out. The solubility of HCl, a strong Brønsted acid in these melts, was measured in melts buffered with LiCl, NaCl, and KCl. The solubility of HCl in all three melts is 450-475 mM under 1 atm of HCl, approximately the same as that in the acidic (AlCl 3 -rich) melts. The relative solubility products of LiCl, NaCl, and KCl were measured, and it was found that K sp (NaCl)/K sp (LiCl) ) 72 ( 6 and K sp (KCl)/K sp -(NaCl) ) 1000 ( 400. It is likely that the differences in the acidity of HCl in the various melts are due to the differences in the solubility product of the relevant alkali metal chlorides. These ratios are consistent with the results of previous studies on the acidity of HCl in the melts. The concentrations of the strongly Lewis acidic Al 2 Cl 7ion in melts buffered with LiCl were measured using an aluminum electrode. The results of the potentiometric work indicate that a melt containing 1 M Li + (approximately n AlCl3 /n EMIC ) R ) 1.25:1 prior to buffering) would contain about 200 µM Al 2 Cl 7 -. This corresponds to a solubility product of about (1.5 ( 0.5) × 10 -12 M 2 . The liquid junction potentials between unbuffered and buffered melts were found to be about 49 mV × ([Li + ]/M). These results are related to previous work on the acidity of HCl in these melts, and it is shown that it is possible to explain many of the acidity and latent acidity results on the basis of the solubility products of the alkali metal chlorides.

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“…This is due to the reaction of the chloride with the acidic anions [Al 2 Cl 7 ] À and [Al 3 Cl 10 ] À forming a ''naked'' superacid proton. 10 The Hammett acidity of these protons has been determined by different groups using both spectroscopic methods 11 and test reactions 12 and values down to H 0 = À18 have been reported.…”

mentioning

confidence: 99%

Effective n-octane isomerization under exceptionally mild conditions using a novel class of superacidic ionic liquids

Meyer

Wasserscheid

2010

Chem. Commun.

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Acidity of HCl in Neutral Buffered Chloroaluminate Molten Salts

Cited by 29 publications

References 16 publications

Approaches to, and Problems with, Ionic Liquid Electrolytes for Alkali Metal Electrochemical Devices: The Case of Low-Melting Chloroaluminate Binary Solutions

Approaches to, and Problems with, Ionic Liquid Electrolytes for Alkali Metal Electrochemical Devices: The Case of Low-Melting Chloroaluminate Binary Solutions

Acidity of Neutral Buffered 1-Ethyl-3-methylimidazolium Chloride−AlCl₃ Ambient-Temperature Molten Salts

Effective n-octane isomerization under exceptionally mild conditions using a novel class of superacidic ionic liquids

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Acidity of HCl in Neutral Buffered Chloroaluminate Molten Salts

Cited by 29 publications

References 16 publications

Approaches to, and Problems with, Ionic Liquid Electrolytes for Alkali Metal Electrochemical Devices: The Case of Low-Melting Chloroaluminate Binary Solutions

Approaches to, and Problems with, Ionic Liquid Electrolytes for Alkali Metal Electrochemical Devices: The Case of Low-Melting Chloroaluminate Binary Solutions

Acidity of Neutral Buffered 1-Ethyl-3-methylimidazolium Chloride−AlCl3 Ambient-Temperature Molten Salts

Effective n-octane isomerization under exceptionally mild conditions using a novel class of superacidic ionic liquids

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Acidity of Neutral Buffered 1-Ethyl-3-methylimidazolium Chloride−AlCl₃ Ambient-Temperature Molten Salts