Static capacitance at the electrochemical liquid-liquid interface between ionic liquids and eutectic Ga-In alloy measured using the pendant drop method

Abstract

Static differential capacitance (Cdc) at the liquid-liquid interface between ionic liquids (ILs) and eutectic Ga-In alloy (EGaIn) has been measured using the pendant drop method for two ILs: 1-ethyl-3-methylimidazolium tetrafluoroborate ([C₂mim⁺]BF₄⁻) and 1-octyl-3-methylimidazolium bis(nonafluorobutanesulfonyl)amide ([C₈mim⁺][C₄C₄N⁻]). The potentials of zero charge for the IL|EGaIn interfaces are shifted compared with the IL|Hg interfaces with an amount that can be considered by the difference in the work functions of EGaIn and Hg. The measured Cdc at the [C₂mim⁺]BF₄⁻|EGaIn interface has well reproduced the camel-shape potential dependence of Cdc at the Hg interface of the same IL at the negatively charged potential region. This suggests that there are little specific interaction between the IL ions with EGaIn and Hg. The [C₈mim⁺][C₄C₄N⁻]|EGaIn has been compared with the [C₈mim⁺]BF₄⁻|Hg interface where IL-cation is the same but IL-anion is different. Also in that case, Cdc is similar to each other at the negatively charged potential region, which means that accumulated C₈mim⁺ ions at the interface mainly govern the Cdc behavior.