Ionic Liquids as Solvents for the Variable Temperature Electrodeposition of Metals and Semiconductors: A Short Introduction

Abedin, Sherif Zein El; Endres, Frank

doi:10.1002/9780470947777.ch7

Cited by 1 publication

(1 citation statement)

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“…1 Although studies on ionics have mainly been performed in aqueous solutions, which limits the types of substances we can handle, over the last 100 years nonaqueous solvent systems (e.g., molten salts, organic molecular liquids, solid oxides, etc.) have also been studied, enabling us to handle often unstable species that have many practical applications, such as Li ion transport in batteries, 2 electrodeposition of elements (e.g., Al), 3,4 and hydride (H − ) transfer 5,6 or conduction. 7,8 Ionic liquids (ILs) are one of the most recent classes of nonaqueous solvent systems to have been established.…”

Section: ■ Introductionmentioning

confidence: 99%

Experimental Insight into the Thermodynamics of the Dissolution of Electrolytes in Room-Temperature Ionic Liquids: From the Mass Action Law to the Absolute Standard Chemical Potential of a Proton

2016

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Room-temperature ionic liquids (ILs) are a class of nonaqueous solvents that have expanded the realm of modern chemistry, drawing increasing interest over the last few decades, not only in terms of their own unique physical chemistry but also in many applications including organic synthesis, electrochemistry, and biological systems, wherein charged solutes (i.e., electrolytes) often play vital roles. However, our fundamental understanding of the dissolution of an electrolyte in an IL is still rather limited. For example, the activity of a charged species has frequently been assumed to be unity without a clear experimental basis. In this study, we have discussed a standard component-based scheme for the dissolution of an electrolyte in an IL, supported by our observation of ideal Nernstian responses for the reduction of silver and ferrocenium salts in a representative IL, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([emim + ][NTf 2 – ] or [emim + ][TFSI – ]). Using this scheme, which was also supported by temperature-dependent measurements with ILs having longer alkyl chains in the imidazolium ring, and the solubility of the IL in water, we established the concept of Gibbs transfer energies of “pseudo-single ions” from the IL to conventional neutral molecular solvents (water, acetonitrile, and methanol). This concept, which bridges component- and constituent-based energetics, utilizes an extrathermodynamic assumption, which itself was justified by experimental observations. These energies enable us to eliminate inner potential differences between the IL and molecular solvents (solvent–solvent interactions), that is, on a practical level, conditional liquid junction potential differences, so that we can discuss ion–solvent interactions independently. Specifically, we have examined the standard electrode potential of the ferrocenium/ferrocene redox couple, Fc + /Fc, and the absolute intrinsic standard chemical potential of a proton in [emim + ][NTf 2 – ], finding that the proton is more acidic in the IL than in water by 6.5 ± 0.6 units on the unified pH scale. These results strengthen the progress on the physical chemistry of ions in IL solvent systems on the basis of their activities, providing a rigorous thermodynamic framework.

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