Ab initio metadynamics study on hydronium ion dynamics at acid-functionalized interfaces: effect of surface group...

Area of Science:

• Computational Chemistry
• Surface Science
• Physical Chemistry

Background:

• Understanding interfacial proton transport is critical for electrochemical applications.
• Hydronium ion (H3O+) mobility is influenced by the local chemical environment.
• Sulfonic acid groups are common in ion-exchange membranes and catalysts.

Purpose of the Study:

• To investigate the effect of surface group density on hydronium ion translocation.
• To determine the activation free energy for hydronium ion transitions under varying surface densities.
• To explore the relationship between surface properties and proton transport mechanisms.

Main Methods:

• Ab initio metadynamics simulations were employed.
• Simulations mimicked minimally hydrated conditions at surfaces with sulfonic acid groups.
• Analysis of frequency spectra was used to determine interaction constants and surface flexibility.

Main Results:

• Hydronium ion translocation is highly sensitive to surface group density.
• A spontaneous concerted transition with a low activation barrier (0.25 eV) occurs at a surface group separation of 6.8 Å.
• Interaction constants and surface group flexibility were determined.

Conclusions:

• Surface group density is a key factor controlling interfacial hydronium ion transport.
• Concerted transitions significantly reduce the activation barrier for proton translocation.
• The findings support and extend the soliton theory of interfacial proton transport.