What does an ion feel at the electrochemical interface? Revisiting electrosorption through nonlocal electrostatics

Area of Science:

• Electrochemistry
• Physical Chemistry
• Surface Science

Background:

• Traditional Gouy-Chapman-Stern theory is limited in explaining ion behavior at metal/electrolyte interfaces.
• Key factors like interfacial water structure and metal electron screening are often overlooked.

Purpose of the Study:

• To develop a more comprehensive model for ion adsorption at metal/electrolyte interfaces.
• To investigate the influence of water molecular structure and metal properties on ion behavior.

Main Methods:

• Combines the method of images with a field-theoretic framework for dilute electrolytes.
• Utilizes the Thomas-Fermi model for metals and a first-order gradient expansion for nonlocal water polarization.
• Avoids the "specular reflection approximation" for boundary conditions.

Main Results:

• Identifies an electrostatic energy minimum for test charges near the interface, dependent on metal screening and potential drop.
• Demonstrates that aligned water dipoles create energy asymmetry for cations and anions.
• Derives an electrosorption isotherm considering potential distribution and lateral charge interactions.

Conclusions:

• Interfacial water structure plays a crucial role in driving ion adsorption.
• The model provides insights into phenomena like underpotential deposition due to favorable electrostatic conditions for ion adsorption.