The Electrode/Ionic Liquid Interface: Electric Double Layer and Metal Electrodeposition

102

Aiming at a comprehensive understanding of the interaction of ionic liquids (ILs) with metal surfaces we have investigated the adsorption of two closely related ILs, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][TFSA] and 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide [OMIM][TFSA], with two noble metal surfaces, Au(111) and Ag(111), under ultrahigh vacuum (UHV) conditions using scanning tunneling microscopy (STM). At room temperature, the ILs form a 2D liquid on either of the two surfaces, while at lower temperatures they condense into two-dimensional (2D) islands which exhibit ordered structures or a short-range ordered 2D glass structure. Comparison of the adlayer structures formed in the different adsorption systems and also with those determined recently for n-butyl-n-methylpyrrolidinium [TFSA](-) adlayers on Ag(111) and Au(111) (B. Uhl et al., Beilstein J. Nanotechnol., 2013, 4, 903) gains detailed insight into the adsorption geometry of the IL ions on the surface. The close similarity of the adlayer structures indicates that (i) the structure formation is dominated by the tendency to optimize the anion adsorption geometry, and that (ii) also in the present systems the cation adsorbs with the alkyl chain pointing up from the surface.

Section: For All Four Adsorption Systems [Emim][tfsa] and [Omim][tfssupporting

confidence: 67%

Interaction of ionic liquids with noble metal surfaces: structure formation and stability of [OMIM][TFSA] and [EMIM][TFSA] on Au(111) and Ag(111)

Uhl

Huang

Alwast

et al. 2015

102

“…A cation is then surrounded by anions and vice-versa. Nevertheless in situ scanning tunnel microscopy (STM) studies have provided evidence of potential-induced transitions in the adsorbed layers of ionic liquids, with the formation of ordered structures on the surface of the electrode 29,30,79,80 [36][37][38] As the imension by B35%, layer entirely (which esent in a concentraeffect the measured t at high concentracation palisade layer in an orientation that is relatively compressed. It is our opinion that the true situation is some combination of the latter two possibilities.…”

Section: A Structurementioning

confidence: 99%

Computer simulations of ionic liquids at electrochemical interfaces

Merlet¹,

Rotenberg²,

Madden³

et al. 2013

154

188

Ionic liquids are widely used as electrolytes in electrochemical devices. In this context, many experimental and theoretical approaches have been recently developed for characterizing their interface with electrodes. In this perspective article, we review the most recent advances in the field of computer simulations (mainly molecular dynamics). A methodology for simulating electrodes at constant electrical potential is presented. Several types of electrode geometries have been investigated by many groups, in order to model planar, corrugated and porous materials and we summarize the results obtained in terms of the structure of the liquids. This structure governs the quantity of charge which can be stored at the surface of the electrode for a given applied potential, which is the relevant quantity for the highly topical use of ionic liquids in supercapacitors (also known as electrochemical double-layer capacitors). A key feature, which was also shown by atomic force microscopy and surface force apparatus experiments, is the formation of a layered structure for all ionic liquids at the surface of planar electrodes. This organization cannot take place inside nanoporous electrodes, which results in a much better performance for the latter in supercapacitors. The agreement between simulations and electrochemical experiments remains qualitative only though, and we outline future directions which should enhance the predictive power of computer simulations. In the longer term, atomistic simulations will also be applied to the case of electron transfer reactions at the interface, enabling the application to a broader area of problems in electrochemistry, and the few recent works in this field are also commented upon.

“…Multilayers of alternating ions with well ordered compact layers of RTILs have been proposed to explain such interfaces. 6,[27][28][29] However, this potential-dependent re-arrangement of cations and anions is not that simple and adsorption-desorption hysteresis 19,22 as well as ultra-slow restructuring 30,31 have also been reported. [13][14][15] Several surface sensitive spectroscopic techniques have been used to investigate RTIL/electrode interfaces, including sum frequency generation (SFG), [16][17][18][19] surface-enhanced Raman spectroscopy (SERS), 20,21 surface-enhanced infrared absorption spectroscopy (SEIRAS), 22,23 subtractive normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) 24 and infrared reflection absorption spectroscopy (IRRAS).…”

Section: Introductionmentioning

confidence: 99%

In situ PM-IRRAS of a glassy carbon electrode/deep eutectic solvent interface

Vieira

Schennach

Gollas

2015

The interface of a 1 : 2 molar choline chloride/ethylene glycol deep eutectic solvent with a glassy carbon electrode has been investigated by polarization modulation reflection-absorption spectroscopy (PM-IRRAS). Temporal spectral changes at open circuit potential show the experiments to be surface sensitive and indicate slow adsorption of electrolyte molecules on the electrode surface. In situ spectroelectrochemical PM-IRRAS measurements reveal characteristic potential-dependent changes of band intensities and wavenumber-shifts in the surface spectra. The potential dependent spectral changes are discussed in terms of adsorption, reduction, desorption and reorientation of choline cations at the interface. Analogies are drawn to the ionic layer structure proposed for the architecture of electrode/ionic liquid interfaces. The results show that in situ PM-IRRAS is generally applicable to glassy carbon electrodes and to electrode interfaces with deep eutectic solvents.