The electrical double-layer structure in KPF₆ methanol + acetone mixtures

Abstract

The influence of binary organic solvents on the double-layer structure has been analysed for a mercury-solution interface without detectable specific ionic adsorption. Electrocapillary curves and the differential capacity were measured for 0.01 M and 0.1 M KPF₆ solutions in a number of acetone + methanol mixtures covering the complete range from pure methanol to acetone. The electrocapillary maximum (ECM) in pure acetone is shifted in the positive direction compared with that in methanol. Similarly, the interfacial tension at the ECM in acetone is lower by 5.5 mN/m than in the 0.1 M KPF₆ methanolic solution. Acetone is selectively adsorbed more strongly on mercury, particularly on the cathodic branch of the capacity or the electrocapillary curves. As previously observed in the literature for the KPF₆ ion in acetone, the capacity peak appears very close to the limit of positive polarization in methanol + acetone mixtures, as well as in pure methanolic solutions.