Differential Capacitance at Au(111) in 1-Alkyl-3-methylimidazolium Tetrafluoroborate Based Room-Temperature Ionic Liquids

Interfacial structures at Au(111) electrode in N-2-saturated 1-alkyl-3-methylimidazolium tetrafluoroborate room-temperature ionic liquids (RTILs) have been studied by the measurements of differential capacitances and cyclic voltammograms. Capacitance-potential (C-E) curves are found to vary significantly with changing the direction of potential scan and temperature. C-E curves measured by sweeping the potential from negative to positive direction always have lower capacitance values compared to the curves measured by reversing the direction of potential scan, and this difference is larger for the RTIL with longer alkyl group. Special arrangement of the ions at the interface in response to the starting potential, constraint in orientation, and change in the ion electrode and ion-ion interactions are presumed to be the causes for this variation. Temperature has a dramatic effect on the Au(111)|EMIBF4 interface. Capacitance around the potential of zero charge decreases with increasing the temperature at the Au(111)|EMIBF4 interface, whereas at the Au(111)|BMIBF4 and Au(111)|OMIBF4 interfaces, it increases, which is discussed on the basis of the effect of temperature on the so-called solidlike crystallinity of RTILs.