Structure and Dynamics at Ionic Liquid/Electrode Interfaces

Abstract

The utilization of ionic liquids (ILs) for future electrochemical applications shows great promise. Recently ILs have been investigated for many electrochemical systems however, further characterization and development of ILs remains as they are utilized in devices such as batteries, capacitors, fuel cells, sensors, and other applications. In this study, we present time resolved (TRS) FTIR spectroscopy data as a means to characterize interfaces between IL-based electrolytes and gold electrodes. These data are important in that dynamic interactions at the electrode/electrolyte interface are crucial to device efficiency, power density, sensitivity, et cetera.

The electrochemical double layer in ionic liquids

“…These timescales are also not uncommon for reorientations and ordering transitions within the IL literature. 64,151,174,205 Our results suggest that hysteresis effects could arise simply from the potential range selected, which is an important aspect not yet fully examined in IL systems. Current literature provides only one report 52 in addition to ours that examines this variable with ILs.…”

“…Upon repetitive cycling of the potential over a 3.2 V range, the spectra indicate that the anion concentration increases (relative to the starting concentration) at an electrode surface even while poised at a strongly negative potential. 64 In another study employing EIS and probe microscopy, two distinctively different processes were detected at the interface between 1ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate and 1-butyl-1methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate ILs and Au (111). A faster, millisecond process is governed by bulk ion transport in the IL due to double layer charging, while a slower process hypothesized to be surface reconstruction of the single crystal electrode took place over several seconds.…”

“…63 Uysal et al 150 suggest that potential dependent hysteresis effects and slow processes during potential steps, which are associated with the reorganization of interfacial IL ions, likely originate from the same mechanism. Hysteresis effects and slow processes, such as the evolution of a probe signal or the change in signal depending on the applied potential direction, have also been demonstrated for the ILelectrode interface from surfaceenhance infrared absorption spectroscopy, 64,152,174 sum frequency generation spectroscopy, 63 X-ray reflectivity, 150,167 and surface plasmon resonance 176 measurements.…”

“…62 Furthermore researchers suggest that once the potential is moved far from the system open circuit potential (OCP), recovering to initial OCP of the electrochemical system is experimentally challenging. 63 Hysteresis effects have also been demonstrated for the ILelectrode interface from surface-enhance infrared absorption spectroscopy, 64,152,174 sum frequency generation spectroscopy, 63 X-ray reflectivity, 150,167 and surface plasmon resonance 176 measurements. Uysal et al 150 hypothesize that potential-dependent hysteresis effects and slow processes during potential steps, which are associated with the (re)organization of interfacial IL ions, likely originate from the same mechanism.…”

“…process was credited to bulk ion transport. 38 IL structural hysteresis was further characterized by surface-enhanced infrared absorption spectroscopy 64,174 and timeresolved X-ray reflectivity 167 for bis(trifluoromethanesulfonyl)imide-based ILs. These reports detailed an ultraslow (several minutes) relaxation of the IL EDL, which has been hypothesized 63,129,150 to be a common feature of ILs at electrified interfaces.…”