Do solvation layers of ionic liquids influence electrochemical reactions?

Abstract

In this discussion paper we discuss our recent results on the electrodeposition of materials and in situ STM/AFM measurements which demonstrate that ionic liquids should not be regarded as neutral solvents which all have similar properties. In particular, we focus on differences in interfacial structure (solvation layers) on metal electrodes as a function of ionic liquid species. Recent theoretical and experimental results show that conventional double layers do not form on metal electrodes in ionic liquid systems. Rather, a multilayer architecture is present, with the number of layers determined by the ionic liquid species and the properties of the surface; up to seven discrete interfacial solvent layers are present on electrode surfaces, consequently there is no simple electrochemical double layer. Both the electrodeposition of aluminium and of tantalum are strongly influenced by ionic liquids: in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py(1,4)]TFSA, aluminium is obtained as a nanomaterial, whereas in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, [EMIm]TFSA, a microcrystalline material is made. Tantalum can be deposited from [Py(1,4)]TFSA, whereas from [EMIm]TFSA only non-stoichiometric tantalum fluorides TaF(x) are obtained. It is likely that solvation layers influence these reactions.

The interface between Au(100) and 1-butyl-3-methyl-imidazolium-bis(trifluoromethylsulfonyl)imide

“…[ 40,41,42].For the Au(111) │ BMIPF 6 interface, the existence of interior and exterior layers next to the surface was reported. Here, the interior layers reveal a distinct reduced layer thickness and need a much stronger force to be ruptured [42].…”

“…Atkin et al and Zhang et al detected several ionic-liquid layers in front of the electrode by measuring AFM force curves [40][41][42]. [ 40,41,42].For the Au(111) │ BMIPF 6 interface, the existence of interior and exterior layers next to the surface was reported.…”

Spotlight on ionic liquids

“…20,21 The popularity of ILs as a research topic is reflected in the numerous reviews, 1,10,22 monographs, 6 and conference proceedings [23][24][25] that have been published recently. The reviews by Hamaguchi and Ozawa 26 and Kobrak, 27 as well as several journal special issues [28][29][30] have focused primarily on the physical chemistry and chemical physics of ILs.…”

Structural Analysis of Ionic-liquid/Organic-monolayer Interface by Phase Modulation Atomic Force Microscopy Utilizing a Quartz Tuning Fork Sensor

“…Several studies have indicated that solvation layers are formed on IL/solid interfaces. [7][8][9][10]28,29 If they were also formed on the HD-SAM/EMI-Tf 2 N interface, there is possibility that the tip scanned on solvation layer formed on the HD-SAM when ¦f was small. After that, ¦f was increased to +50 Hz and the tip scanned the inside of the solvation layer, where the topographic feedback became unstable.…”

“…Recently, several force curve studies on IL/solid interfaces using contact-mode AFM have been reported and they have revealed the presence of the solvation layers on the interface. [7][8][9][10] Nevertheless, contact-mode AFM has disadvantage on lateral resolution and in fact, high-resolution lateral imaging on IL/solid interfaces was mainly carried out by scanning tunneling microscopy (STM). It is well known that STM is capable of atomic-resolution imaging on conductive materials such as metals and semiconductors.…”