Surface Charge Density Spectra: Complex Analysis of the Electrical Double Layer Developed from Measurements of Hexanol Adsorption Kinetics

A procedure for deriving surface charge density spectra from differential capacitance data is presented in this study, providing a deeper analysis of the generated charge. A set of simulated differential capacitance spectra was determined for three types of adsorption process control: diffusion control, adsorption control, and mixed control. Based on the differential capacitance curves and spectra, surface charge density spectra were determined. Shapes characteristic of the three types of control of the adsorption process were identified. Using the Dynamic Electrochemical Impedance Spectroscopy (DEIS) technique, the kinetics of hexanol adsorption on a mercury electrode was analyzed. A change in the controlling step of the hexanol adsorption process from diffusion control to adsorption control was observed, based on the relaxation time values and differential capacitance spectra shape. Using a procedure developed on the basis of simulated data, the surface charge density spectra were determined over the entire range of investigated potentials. The developed procedure enabled the separation of the electric double layer (EDL) capacitance from the adsorption pseudocapacitance over a wide potential range. The charges associated with the EDL and generated by increasing pseudocapacitance were determined. The contribution of both charges to the total charge generated with a change in electrode potential varied with the electrode potential.