Electrical Double-Layer Structure in Ionic Liquids: A Corroboration of the Theoretical Model by Experimental Results

Abstract

We experimentally observed for the first time a bell-shaped (convex parabolic) differential capacitance versus potential (C dl -E) curve, which is expected according to the theory of Kornyshev given for the electrical double layer (EDL) of metal electrode/ionic liquid (IL) interface, at platinum and gold electrodes in four different [quaternary ammonium, imidazolium, and pyrrolidinium cations and bis(trifluoromethanesulfonyl)imide anion-based] ILs with cations and anions of similar sizes. The C dl -E curves measured at a glassy carbon (nonmetallic) electrode in the same set of ILs were found to be U-shaped, in contrast to those obtained at platinum and gold electrodes. The present study corroborates the so-called Kornyshev's model of the EDL at metal electrode/IL interfaces and at the same time demands a theoretical model for the nonmetallic electrode/ IL interface. The EDL formation in ILs is discussed.

Mean-Field Theory of Electrical Double Layer In Ionic Liquids with Account of Short-Range Correlations

“…7 this law should work not when u 0 >> 1, but when αu 0 >> 1. In other words it should be observed at higher voltages (which is very much in line with experimental observations and simulations) [2,16,17,29,[37][38][39]75]. The physical meaning why α disappears from this law is clear: α represents resistance to crowding, but when Eq.…”

“…(30) into (27) we obtain asymmetric differential capacitance curves. The plot displayed in Figure 4 corresponds to the case of smaller anions than cations, which is often seen in experiments [2,16,17,[37][38][39].…”

“…A renowned Feature Article Ref. 7 has set a tone in this development and triggered a flow of theoretical , as well as experimental [37][38][39][40][41][42][43], works in this area. A simple theory was presented in that paper which predicted 'bell' or 'camel' shaped differential capacitance-potential curves, instead of Gouy-Chapman (GC) U-shape differential capacitance-potential dependence.…”

Some Analytic Expressions for the Capacitance and Profiles of the Electric Double Layer Formed by Ions Near an Electrode

“…This behavior was first predicted by Kornyshev [33] on the basis of a lattice theory and seems to be universal. As well as the simulations of Henderson and Lamperski, it has been seen experimentally 43 (2) by Islam et al [35]. Something of the nature of…”

“…As well as exposing the deficiencies of the GCS theory, EDLs in ionic liquids are important in green technologies, the design of novel energy storage devices, such as high-tech batteries and super-capacitors [34]. Ionic liquid DLs have attracted recent experimental [35,36] and theoretical interest [18][19][20][21][37][38][39]. The differential capacitance, as determined by MC simulations, of a simple model [38] of an ionic salt in which T * = 0.8 and d = 8 Å is given in Fig.…”