Analytical Interfacial Layer Model for the Capacitance and Electrokinetics of Charged Aqueous Interfaces

Area of Science:

• Physical Chemistry
• Materials Science
• Electrochemistry

Background:

• Solid-electrolyte interfaces are critical in various electrochemical applications.
• Understanding the properties of the subnanometer interfacial layer is essential for optimizing device performance.
• Existing models often simplify or neglect the complex behavior of this interfacial region.

Purpose of the Study:

• To develop an analytical model incorporating a subnanometer interfacial layer.
• To investigate the influence of this layer on differential capacitance and electro-osmotic mobility.
• To extract interfacial layer properties from macroscopic experimental data.

Main Methods:

• Constructed an analytical model integrating a box model for interfacial properties into Poisson-Boltzmann and Stokes equations.
• Calculated differential capacitance and electro-osmotic mobility as functions of surface charge density and salt concentration.
• Compared model predictions with experimental data for graphite, silver, titanium oxide, and silver iodide.

Main Results:

• The model successfully reproduced experimental differential capacitance for silver interfaces.
• An additional capacitance component was needed for graphite interfaces.
• A power-law dependence for electro-osmotic mobility at high surface charges was observed and explained.
• A finite-viscosity layer provided a better fit for electro-osmotic mobility than hydrodynamic slip.

Conclusions:

• The analytical model effectively captures the impact of subnanometer interfacial layers.
• The model allows for the extraction of interfacial layer properties from experimental measurements.
• Findings provide insights into the fundamental behavior of solid-electrolyte interfaces.