Structure and dynamics of the interfacial layer between ionic liquids and electrode materials

Abstract

In this paper we present a combined in situ STM, AFM and EIS study on the structure and dynamics of the interfacial layers between Au(111) and two extremely pure ionic liquids, namely [Py 1,4 ]FAP and [EMIM]FAP. The combination of these methods provides valuable information for both neutral and electrified interfaces. In situ STM and AFM results reveal that multilayered morphology is present at the IL/Au(111) interface, with stronger near surface layering detected at higher electrode potentials. The in situ STM measurements show that the structure of the interfacial layers is dependent on the applied electrode potential, the number of subsequent STM scans and the scan rate. Furthermore, in the case of [Py 1,4 ]FAP, the Au(111) surface undergoes herringbone reconstruction, Au(111)(22 x √3), in the cathodic potential regime, and the ultra-slow formation of vacancies in the herringbone structure is probed with in situ STM. EIS measurements reveal the presence of two distinct capacitive processes at the interface taking place on different time scales. The time scale of the fast process is typically in the millisecond range and is governed by the bulk ion transport in the IL, which exhibits a Vogel-Fulcher-Tammann-type temperature dependence. The slow process takes place on a time scale of seconds and is Arrhenius activated. The contribution of this process to the overall interfacial capacitance is

Ionic Liquids in Catalysis

“…IL surface properties have been investigated by numerous surface-sensitive spectroscopic techniques and scattering methods. Initially, these studies were mainly restricted to methods that can be applied under ambient conditions, such as sum-frequency generation (SFG) [100,[109][110][111][112][113][114][115][116], X-ray reflectivity and neutron reflectometry [112,[117][118][119][120][121], grazing incidence X-ray diffraction [122], atomic force microscopy (AFM) [104,[123][124][125][126][127][128][129][130][131][132][133][134] and surface force balance (SFB) [135][136][137]. In 2005, it was realized that the surface properties of ILs can also be investigated using the well-developed techniques of ''classical'' surface science.…”

Electrochemical impedance spectroscopy in interfacial studies

“…4. Atkin et al [8] measured impedance for Au(111) electrode in two ionic liquids obtaining apparently good quality data. However, by fitting Cole-Cole functions to the frequency normalized admittances of the electrodes instead of the interfaces, the electrolyte resistance blurred the determined capacitances.…”

Ionic Liquid-Modified Electrocatalysts: The Interaction of [C 1 C 2 Im][OTf] with Pt(1 1 1) and its Influence on Methanol Oxidation Studied by Electrochemical IR Spectroscopy

“…photoelectron spectroscopy, vibrational spectroscopy and scanning probe microscopy, it could be shown that ILs show very specific ion-surface interactions [23][24][25], may undergo interfacial reaction [25,26], and may form layered [27][28][29] and even ordered structures at noble metal surfaces [30][31][32][33][34][35][36]. On electrochemically controlled surfaces either the cation, or the anion or both are adsorbed at the electrode surface depending on the electrode potential [30,[32][33][34][35]37]. In their electrochemical STM studies on Au(111), for instance, Magnussen and coworkers recently showed that a variety of different ordered structures are formed as a function of the potential [30].…”

“…In their electrochemical STM studies on Au(111), for instance, Magnussen and coworkers recently showed that a variety of different ordered structures are formed as a function of the potential [30]. Atkin et al recently reviewed the pioneering work of several groups on the structure formation at IL-Au(111) interfaces [37]. The work shows that structure formation occurs not only at the interface but over several monolayers into the electrolyte and involves processes on timescales that span many orders of magnitude.…”