(722e) Challenges of Modeling Electrochemical Processes: Electrical Double Layer on Charged Electrode Surface

Electrochemical processes are considered greener and have drawn much attention in the past decades. However, current commercial process simulators are not capable of modeling electrochemical systems yet. Gaps exist between the industrial application and available modeling tool due to the complexity of electrochemical systems with additional non-ideality introduced by the external electric field. The double layer is formed on the electrode surface as electrode is charged and perturbs the surface concentration and the electric potential in the solution. The electrode reaction rate cannot be determined without understanding the double layer structure specifically the ion concentration and the effective electric potential distributions.

This presentation will focus on modeling the double layer structure on the charged electrode surface. The surface concentration is not directly measurable but can be indicated by differential capacitance data, defined as change of potential difference between electrode and solution with surface charge density. The proposed model will be validated by comparing with capacitance data obtained from aqueous electrolyte solution on mercury electrode. The double layer can be separated into the diffuse layer and the inner layer. The diffuse layer can be described by classic Gouy-Chapman-Stern theory and the inner layer capacitance is attributed to water and ion adsorption on the surface. We proposed an activity-based model to describe the species adsorption under influence of electric field and chemical interaction with electrode surface. The model will be firstly applied to systems in the absence of ion adsorption, where reorientation of water dipoles is responsible for the potential difference in the inner layer. The model will be further extended to systems that have specific ion adsorption on the electrode surface. This work is expected to provide a thermodynamic framework with a well-described double layer structure that can be used to study electrode reaction kinetics. The model can be easily incorporated with current commercial simulator and contribute to modeling electrochemical processes.