Ionic Liquid Structure Dependent Electrical Double Layer at the Mercury Interface

Abstract

Structures of the electrical double layer at Hg|room-temperature ionic liquid (RTIL) interfaces were studied by measuring the differential capacitance and electrocapillary curves as a function of potential. Maxima of the electrocapillary curves measured at the Hg|1-hexyl-3-methylimidazolium tetrafluoroborate (HMIBF4) and 1-octyl-3-methylimidazolium tetrafluoroborate (OMIBF4) interfaces demonstrate an unusual broadness on the anodic side of the potential of zero charge (PZC), which is significantly different from those obtained at Hg in RTILs containing shorter alkyl chains or in conventional molecular solvents containing electrolytes. This broadness of the electrocapillary curve was found to depend on the crystal structure and spatial heterogeneity of the RTILs containing larger alkyl groups, which impede the charged moieties from being in contact with the electrode surface within a certain potential range. Cleaving of the liquid crystal structure by the dilution of OMIBF4 with dimethyl sulfoxide, which i...