Interfacial ionic ‘liquids’: connecting static and dynamic structures

Abstract

It is well known that room temperature ionic liquids (RTILs) often adopt a charge-separated layered structure, i.e. with alternating cation- and anion-rich layers, at electrified interfaces. However, the dynamic response of the layered structure to temporal variations in applied potential is not well understood. We used in situ, real-time x-ray reflectivity to study the potential-dependent electric double layer (EDL) structure of an imidazolium-based RTIL on charged epitaxial graphene during potential cycling as a function of temperature. The results suggest that the graphene-RTIL interfacial structure is bistable in which the EDL structure at any intermediate potential can be described by the combination of two extreme-potential structures whose proportions vary depending on the polarity and magnitude of the applied potential. This picture is supported by the EDL structures obtained by fully atomistic molecular dynamics simulations at various static potentials. The potential-driven transition between the two structures is characterized by an increasing width but with an approximately fixed hysteresis magnitude as a function of temperature. The results are consistent with the coexistence of distinct anion- and cation-adsorbed structures separated by an energy barrier (∼0.15 eV).

Copper-Tin Alloys for the Electrocatalytic Reduction of CO2 in an Imidazolium-Based Non-Aqueous Electrolyte

“…The addition of 100 mM [BMIM] + to the N 2 -saturated MeCN containing 0.1 M TBAPF6 ( Figure 5, left) causes an increase of charge stored within the double layer region [29,30], which may be presumed to be due to the adsorption of [BMIM] + at the electrode/electrolyte interface of the negatively polarized CuSn film [31][32][33]. Similar phenomena have been observed for Au electrodes [34][35][36][37], and it has been demonstrated that [Im] + cations prefer to π-stack and lie flat on electrode surfaces, thereby supporting more capacitive charge build-up than an inner layer containing large TBA + cations [38][39][40].…”

Topological defects in electric double layers of ionic liquids at carbon interfaces

“…This is the first time the degree of ion ordering can be directly visualized and analyzed through imaging techniques with a lateral resolution of around 20 nm. This will allow for comparison of the AFM result with X-ray and neutron scattering techniques performed on similar systems in the future [16,38]. All the dislocations marked in Regions I-III show the same general behavior but it happens over different lengths scales between 50 and 80 nm.…”

Molecular scale structure and dynamics at an ionic liquid/electrode interface

“…Time resolved experiments, covering the relaxation dynamics on the seconds to minute scale, indicated the presence of ultraslow interfacial processes. 31,32 Scanning tunneling microscopy and AFM studies indicate that the substrate-adsorbed cation layer is affected by an applied potential. 20,28,[33][34][35] Sum frequency generation (SFG) spectroscopy 36 detected molecular reorientations upon variation of the applied potential.…”