A NEW ANALYSIS OF THE DIFFERENTIAL CAPACITANCE OF AN IDEALLY POLARIZED ELECTRODE .2. NONAQUEOUS SOLVENTS

A previously presented analysis of the differential capacitance of an ideally polarized electrode without ionic specific adsorption is used for investigating the interface between a mercury electrode and a non-aqueous electrolyte solution. Capacitance data for eight non-aqueous solvents are considered. The solvent contribution C(s) is obtained by separating from the inner layer capacitance C(i) deduced from experiment the contribution C(m) related to the relaxation with charge of the surface dipole of the metal and to the variation with the electrode charge sigma of the distance of closest approach of the solvent molecules to the metal surface. The C(s)(sigma) curves are found to be specific to each solvent but all curves have a common simple shape and a single maximum in the range of charges explored. For all solvents but methanol and acetonitrile this maximum is either at a negative charge close to the pzc. The size of the solvent molecule is found to play an important role in the magnitude of C(s) near its maximum. The contribution C(dip) originating from the orientation of the permanent dipoles is analyzed. A clear separation between associated and non-associated solvent is evidenced. The influence of the physical parameters of the solvent and the nature of intermolecular interactions is discussed.