Measurement of Physical Adsorption of Neutral Organic Species at Solid Electrodes

Chronocoulometry recorded during the first 100 ms of double layer charging has been used to study the physical adsorption of neutral organic molecules on solid electrodes. The adsorption of cyclohexanol on gold is used to illustrate the method. The film pressure and the Gibbs surface excess for this system are determined as functions of potential from charge densities obtained by the analysis of the potentiostatic transients. Charge densities determined by chronocoulometry are compared with results obtained from the integration of differential capacities, which were independently measured at 25 Hz. Film pressures determined from these differential capacity measurements are shown to be unrealistically low and inconsistent with changes in bulk cyclohexanol concentration. In contrast, chronocoulometry gives consistent results and allows the determination of results that are comparable to those obtained on mercury.