(427e) Incorporating Electrode-Electrolyte Interfacial Effects on the Specific Adsorption of Ions on Late Transition Metal Surfaces Using a Combined DFT/FF-MD Approach

Ions within the electrolyte have pronounced effects on the kinetics of electrocatalytic reactions in batteries, fuel cells, and electrolysis cells. Specific ion adsorption can competitively adsorb to active sites and interact strongly with the interfacial electric field, altering the interfacial structure of the electrochemical double layer (EDL). Incorporating the effects of the local electric field and interfacial solvation on specific ion adsorption is important in the development of electrocatalysts. Our group has previously developed a compartmentalized Helmholtz approach to model elementary electrocatalytic reaction energetics and activation barriers, where barriers of species with large changes in dipole moments (for NH* to NH₂*) are sensitive to the EDL properties. We extend this compartmentalized approach to investigate the potential dependence of ion specific adsorption equilibrium. We used DFT calculations to quantify the specific interactions between (hydrated) ions and the electrode surface, and between ions and specific solvent molecules. Force-field molecular dynamics (FF-MD) simulations are then used to evaluate extended ion-solvent and ion-electrified interface interactions, which the predicted EDL properties are then used to inform the compartmentalized model that evaluates the impact of EDL dielectric polarizability and electric field distributions on ion adsorption.

We determined the equilibrium adsorption potential where specific adsorption of anions and alkali earth metal ions would adsorb across a series of late transition metal surfaces. We observed that adsorption equilibrium potentials can vary by over 1 V depending on the approach used to include EDL effects, varying from implicit solvation models, explicit H₂O molecules, or from a FF-MD description. Incorporation of the interactions between the local electric field effects and the ions significantly affect the adsorption energies of ions with larger surface dipole moments. The solvent structures around the ions and how they change with applied potential are investigated using FF-MD to correlate their effects to the adsorption of ions.