Catalyst synthesis and many catalytic reactions occur at the interface between a charged solid electrode and an aqueous electrolyte. The structural and dynamic properties of water and electrolytic ions at this interface can impact transport and reaction kinetics. For example, varying cation identity and concentration in the electrolyte influences activity and selectivity in the CO2 reduction reaction. Atomistic simulation of the electrode-electrolyte interface is needed to examine such cationic effects, and more generally how electrolyte properties can be used to influence catalytic processes. In this talk, I will present our efforts in modeling the electrode-electrolyte interface using both DFT and classical force-field molecular dynamics (MD). Firstly, we determine the dielectric constant profiles of water on an Ag(111) electrode surface. We found the dielectric behavior of water at &lt;1nm from the metal surface starkly distinct from bulk water. A clear anisotropic feature is observed, with the in-plane dielectric constant enhanced and the out-of-plane dielectric constant negative, suggesting an over-screening behavior. Next, by using the potential of mean force, we map out the free energy surface of bringing the cations from bulk toward the electrode surface. We furthermore decouple the contribution of the ion-metal interactions from the ion-water interactions. The solvation thermodynamics of the cations is further investigated by calculating their solvation free energies (free energy relative to a gas phase) and also delineating the enthalpic and entropic contributions to solvation. The solvation thermodynamics of the cations is then connected back to the measured dielectric constants. Finally, DFT was used to capture the electronic signature of adsorbing cations such as charge transfer. Integrating DFT electronic structures with solvation thermodynamics from classical MD results in a rigorous atomistic picture of cation adsorption, paving the way for future study of cationic effects in electrocatalysis.

Atomistic DFT/MD model for water structure, dynamics, and ion distribution at catalyst-electrolyte interfaces

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