Electrosorption of 2,2-Dimethyl-1-propanol on silver(111). A Comparison between capacitive charge and differential capacity measurements

The adsorption of 2,2-dimethyl-1-propanol (neopentyl alcohol, NPA) on a Ag(111) single-crystal electrode surface from aqueous 0.05 M KClO4 as a function of the applied potential E was investigated on the basis of measurements of the capacitive charge óM by a computerized chronocoulometric apparatus and of the differential capacity C by a frequency response analyzer. A satisfactory agreement was found between directly measured C vs E curves and those obtained by numerical differentiation of the corresponding óM vs E curves. Adsorption isotherms at constant E and at constant óM were determined on the basis of a thermodynamic analysis of capacitive charge data. The standard Gibbs energy of adsorption, ¢G°ads, was determined as a function of E and of óM, and attains a minimum value of -12.6 kJ mol-1 at E ) -0.77 V/SCE and óM ) -1.1 íC cm-2. The results of the thermodynamic analysis of adsorption data at the potential of maximum adsorption were compared with those of an extrathermodynamic analysis based on the Frumkin two-parallel capacitors model.