No abstract

No abstract

No abstract

The thermodynamics of pyrazine adsorption onto a polycrystalline gold electrode was investigated quantitatively by employing chronocoulometry. The measurement of the charge density on the metal side of the metal-solution interface allowed the determination of the adsorption parameters. The film and surface pressures, the relative Gibbs surface excesses, the free energies of adsorption, and the electrosorption valency as functions of both electrode potential and surface charge density were calculated. The maximum Gibbs surface excess found for pyrazine is 5.8 X 1CT10 mol cm"2. The Gibbs free energy of adsorption determined at the potential and charge of maximum adsorption (0.25 V (SCE) and 17.5 /uC cm"2, respectively) is equal to -32.8 kJ mol"1. The adsorption of pyrazine on Au and Hg is compared, and the differences in the orientation of pyrazine molecules at the two interfaces are also discussed. In addition, the similarities between the adsorption of pyrazine and pyridine on a polycrystalline gold electrode are described.

Adsorption of coumarin on an Au(210) single-crystal electrode was investigated using chronocoulometry and phase-sensitive a.c. voltammetry. The adsorption parameters, such as the relative Gibbs surface excess, the Gibbs energies of adsorption and the electrosorption valencies, were calculated. The results suggest that coumarin molecules assume a flat, -bonded orientation on the Au(210) surface. The zero coverage Gibbs energy of adsorption at the potential of maximum adsorption is À42 kJ mol À1 , which is a value typical of chemisorption. The adsorption of coumarin on the Au(210) surface was compared with adsorption at the (111) and (100) planes of gold.