Atypical electric behavior of the double layer. Experimental case studies: Rh(111) in aqueous HCl solutions, and Au(111) in an ionic liquid, BMIPF6

Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and zero-charge-potential measurements have been performed for the title systems. The results of the Rh(111)/aqueous HCl solutions demonstrate that in solutions of binary electrolytes with adsorbing anions the interfacial impedance is a single, indivisible element, even if its frequency dependence implies a four-element circuit. The measurements on Au(111) in 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF6) reveal that double-layer formation and rearrangement in ionic liquids are very slow processes manifesting themselves as a parallel combination of a capacitance and a constant phase element (CPE).