Parameter-Fitting-Free Continuum Modeling of Electric Double Layer in Aqueous Electrolyte

Area of Science:

• Physical Chemistry
• Computational Materials Science
• Electrochemistry

Background:

• Electric double layers (EDLs) are crucial in electrochemistry, but accurate modeling remains computationally demanding.
• Existing models often require extensive parameter fitting, limiting their predictive power and applicability.
• Challenges persist in capturing the complex interplay of microscopic interactions within EDLs.

Purpose of the Study:

• To develop a predictive multiscale continuum model for EDL structure that eliminates the need for parameter fitting.
• To incorporate novel microscopic interactions, including solvation shell polarization, parallel plane electrostatic interactions, and ion-size-dependent entropy.
• To provide a computationally efficient tool for understanding and predicting EDL behavior.

Main Methods:

• A multiscale continuum model was developed based on minimizing the total grand potential of the system.
• The model incorporates newly introduced microscopic interactions: solvation polarization, parallel plane electrostatic interaction, and ion-size-dependent entropy.
• Model parameters were derived from independent experimental literature data for electrode and electrolyte materials.

Main Results:

• The model successfully reproduced experimental differential capacitance trends for Ag(110) and Hg electrodes with non-adsorbing electrolytes.
• Calculations indicated that electron stability changes rationalize observed differential capacitance values.
• Sensitivity analyses identified key material properties (ion radius, valence, electrode Wigner-Seitz radius, bulk modulus) governing EDL structure.

Conclusions:

• The proposed predictive multiscale continuum model offers accurate EDL structure prediction with low computational cost.
• The model's ability to reproduce experimental data validates its predictive capability and the significance of incorporated microscopic interactions.
• While successful for several systems, the model suggests the need for incorporating electrode/ion-specific interactions for certain materials like Pt(111).