Impedance spectra (50kHz–1Hz) were acquired and used to obtain the differential capacitance at the interfaces between 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6] ionic liquid and three different electrode materials (Hg, Pt, and glassy carbon (GC)) as a function of the applied potential. The electrocapillary curve for the Hg/[BMIM][PF6] interface was obtained from drop time measurements, from which the potential of zero charge was calculated to be −0.39V (Ag wire). The potential of zero charge is 0.30V less negative than the potential of differential capacitance minimum. This disagreement suggests that the differential capacitance minimum is not related to a classical diffuse layer minimum. Additional support to this conclusion was obtained from positive temperature coefficient for the differential capacitance in contrast to the negative temperature predicted by the classic Gouy-Chapman model. The results do not support the recent model predictions of bell shaped capacitance curves for room temperature ionic liquids, RTILs.