Calculating adsorption parameters of organic substances from the capacitance curves in the absence of information on the electrode zero-charge potential in a supporting electrolyte solution

The possibility of estimating the potential of zero charge (PZC) of an electrode in a supporting electrolyte solution (SES) from the differential capacitance vs. potential dependences measured in SES and in the presence of different amounts of organic substances is analyzed by using model calculations. It is shown that the electrode PZC in SES cannot be uniquely determined in the model of two parallel capacitors and Frumkin isotherm which are commonly used for describing the organic substance adsorption. It is shown that all adsorption parameters, with the exception of the adsorption potential drop of the organic substance, can be calculated from capacitance curves in the absence of information on the electrode PZC. From the analysis carried out it follows that, under given conditions, the potential of the organic-substance maximum adsorption is an adsorption parameter on the same scale as is used for differential-capacitance measurements.