Electrochemical investigation of 1,5-pentanediol adsorption on the Ag(111)and Ag(110) faces

The electrosorption of 1,5-pentanediol (PD) on a Ag(111) single-crystal ele ctrode surface was investigated from aqueous 0.05 M KClO4 on the basis of c hronocoulometric measurements of the capacitive charge sigma(M) and of diff erential capacity measurements. The sluggishness of the PD adsorption/desor ption step prevented differential capacity measurements under conditions of adsorption equilibrium, other than in the neighbourhood of the potential o f maximum adsorption. Chronocoulometric measurements do not suffer from thi s limitation. Adsorption isotherms at constant potential E and at constant sigma(M) were therefore determined on the basis of a thermodynamic analysis of chronocoulometric sigma(M) versus E plots at different PD concentration s. The potential dependence of the electrosorption valency was found to be determined mainly by the reorientation of the water dipoles under the inter facial electric field. The adsorption isotherm at the potential of maximum adsorption. E-m, obtained by the thermodynamic procedure, was compared with that obtained from differential capacity data via an extra-thermodynamic p rocedure based on the Frumkin two-parallel capacitors model. The latter pro cedure was also adopted to estimate the adsorption isotherm of PD on Ag(110 ) at the potential of maximum adsorption. The absolute value of the standar d Gibbs energy of adsorption at E-m decreases in passing from Ag(111) to Ag (110), namely with an increase in the hydrophilicity of the face. (C) 1999 Elsevier Science S.A. All rights reserved.