The structure of the electrical double layer in the presence of adsorbed organic molecules

On the model of the electrical double layer previously proposed by the author, equations are derived for the differential capacity of the metal/electrolyte interface in the presence of organic molecules. It is shown that the equations apply even when ions are specifically adsorbed. A method of calculating the amount of adsorption of the organic species from differential capacity data is outlined and applied to published results for thiourea at the mercury aqueous sodium fluoride interface. It is shown that the results are in good agreement with thermodynamic data. From the calculated adsorption d a ta it is shown that thiourea obeys a virial equation of state but that lateral electrostatic forces are probably negligible except at high coverage. The free energy of adsorption as a function of charge has been evaluated and shown to consist of an electrostatic term and a chemical term which decreases as the electron density of the mercury surface decreases.