Capacitance and ionic association at the electrified oil ∣ water interface: the effect of the oil phase composition

The capacitance of the polarisable aqueous ∣ organic interface was measured with the impedance method, varying both the solvent and the electrolyte of the organic phase. The results were analysed using the idea of interfacial ion-pairing presented earlier (J. Chem. Soc. Faraday Trans. 87 (1991) 107). It appeared that this model was capable of explaining the measured capacitances quite well for 2-heptanone, 2-octanone and 1,3-dibromopropane as the organic solvent, while for 1,2-dichloroethane — which is perhaps the most common solvent used in liquid ∣ liquid electrochemistry — the model needed to be modified, assuming a mixed layer between the bulk solvent phases as suggested earlier in the literature.