Method for Evaluating the Surface Concentrations of Two Like-Charged Ions Simultaneously Adsorbed at an Electrode-Solution Interface

摘要

A recent preliminary report by Gonzales and co-workers highlights the experimental difficulties in determining the amounts of specific adsorption of two types of ions simultaneously present at a mercury-aqueous interface. The authors note that the elegant analysis of Lakshmanan and Rangarajan required such a large amount of data that the method has scarely ever been employed. There are additional difficulties with this analysis when employed at solid electrode surfaces. It is desirable to find a method that could readily be applied at polycrystalline solid, as well as liquid, electrodes. This reports outlines such an analysis for determining the simultaneous adsorption of like-charged ions, based on a simple extension of the well-known Hurwitz-Parsons approach. These authors demonstrated independently that the amount of specific adsorption of, for example, an anion X can be assessed from differential capacitance-potential data for a series of mixed electrolytes containing varying proportions of the salts BX and BY at a constant total ionic strength, where Y is an anion that is not specifically adsorbed. The electrocapillary equation can be written in terms of salt chemical potentials.