Capacitance Measurements in a Series of Room-Temperature Ionic Liquids at Glassy Carbon and Gold Electrode Interfaces

Abstract

An extensive study has been done for the first time on the structure of the electrical double layer (EDL) at polarized glassy carbon (GC) and gold (Au) electrode interfaces in a series of room-temperature ionic liquids (RTILs) via the measurement of capacitance-potential curves. The parabolic capacitance-potential curves similar to those observed in high-temperature inorganic molten salts were obtained at GC electrode in all of the RTILs studied. Potential of zero charge (PZC) at GC electrode in imidazolium-based RTILs depends significantly on the electrochemical pretreatment of the electrode surface: Electrochemical oxidation pretreatment generates the oxide surface on GC electrode, which results in a favorable adsorption of positively charged imidazolium cations on the electrode surface and in turn shifts the PZC to the positive direction of potential, whereas at the electrochemically reduced GC electrode, on which the adsorption of the imidazolium cations is less favorable, PZC shifts to the negative direction of potential. Such an effect of electrochemical pretreatment was not observed at the highly oriented pyrolytic graphite electrode. The hump on the anodic side of the capacitance-potential curves at Au electrode in imidazolium-based RTILs results from the π-electronic interaction of the imidazolium ring with the metal electrode, which was substantiated by using nonmetallic electrode and varying the ions of the RTILs. Such an enhanced interaction of the imidazolium ring with a gold electrode, as in the case of anion adsorption, shifts the PZC to the negative direction of potential. Such a hump as that observed at the gold electrode was not observed at the GC electrode. Similarly to the case in high-temperature inorganic molten salts, capacitances at PZC increase with increasing temperature. Different aspects of the obtained capacitance-potential curves are interpreted satisfactorily based on the hitherto proposed concept of the EDL structures.

Fused coarse-grained model of aromatic ionic liquids and their behaviour at electrodes

“…The results from the 3-bead CG model also display close values as Hu et al 27 Feng and co-workers also provided some results for the same IL in room temperature via atomistic simulation, the capacitances are about 6-8 µF/cm 2 , which are between our results and the previous two literatures. 46 But the overall values in our results are close with the experimental works by Alam et al 47 The reason that causes the differences might be different force fields of ILs, as well as various parameters for the electrodes. Ac- tually, the capacitances varies under different conditions, for example, temperatures.…”

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

“…Estimates based on Israelashsvili's publications generate capacitance curves behaving as GC at moderate potentials. Such behaviour is seen for some electrodes such as HOPG [78,79], but this is believed to be from the contribution of the space charge in semi-metallic graphite electrode rather than the double layer in ionic liquid (for analysis of those contributions see Ref. 31 and citations therein).…”

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

“…Up to now, differential capacitance curves have been measured on different electrodes including liquid metal Hg, [56,95,96] solid metals Au [29,97,98] and Pt, [83,84,[97][98][99] glassy carbon (GC), [48,97,98,100] and HOPG. [98,100] The ionic liquids involved are mainly with alkylimidazolium-based cations.…”

“…Up to now, differential capacitance curves have been measured on different electrodes including liquid metal Hg, [56,95,96] solid metals Au [29,97,98] and Pt, [83,84,[97][98][99] glassy carbon (GC), [48,97,98,100] and HOPG. [98,100] The ionic liquids involved are mainly with alkylimidazolium-based cations. Bell-shaped, [29,97] camel-shaped, [48] and even parabolic [56,83,84,[95][96][97][98]100] capacitance curves have been obtained depending on the electrodes and ionic liquids employed, which exclude the possibility to determine the PZCs from differential capacitance curves in ionic liquids by a universal rule.…”

“…[98,100] The ionic liquids involved are mainly with alkylimidazolium-based cations. Bell-shaped, [29,97] camel-shaped, [48] and even parabolic [56,83,84,[95][96][97][98]100] capacitance curves have been obtained depending on the electrodes and ionic liquids employed, which exclude the possibility to determine the PZCs from differential capacitance curves in ionic liquids by a universal rule.…”