(450e) Solvation Effects on Electrocatalytic Reaction Barriers through Multiscale Modeling of the Electrochemical Double Layer

Electrocatalysis is pivotal in sustainable energy conversion, enabling processes such as green hydrogen production and carbon dioxide conversion using renewable sources. However, electrification of the interface poses challenges to rational design, as interactions among the charged electrocatalyst, solvation layer, electrolyte countercharge, and adsorbed reaction intermediates dictate catalytic activity and selectivity. Atomistic-scale modeling is hindered by the complex dynamics of reactions and electrolyte structures. Quantum mechanical (QM) methods are essential for accurate representation of reactions but limited by the computational cost of modeling the dynamic ensemble of structures representing the electrochemical double-layer (EDL). Representing elementary electrochemical reaction paths and activation barriers is particularly challenging due to involving both electron and ion transfer from the electrolyte. A combination of methods, integrating quantum mechanics, continuum theories, and force-field molecular dynamics (FF-MD), is necessary to connect EDL composition, structure, and catalytic performance.

We introduce a combined multiscale density functional theory (DFT) and FF-MD model to represent the EDL in determining elementary reaction energies and activation barriers. DFT calculations capture the local electronic structure of adsorbates on electrocatalysts, incorporating explicit H₂O molecules to represent local solvation along the reaction coordinate. This is combined with an FF-MD model of the double layer, incorporating complex solvation effects and ion distribution in a fully electrified model. A classical dynamic charge approach ("QDyn") simulates charge movement in response to electrolyte dynamics, enabling simulations of nanoseconds over modest computational resources. By employing a frozen solute approximation, DFT optimized structures are inserted into the FF-MD simulation to examine variations in solvation energies along a reaction path. This analysis assesses activation barriers as a function of electrode potential and changes in double layer properties. Our model predicts that reaction processes with significant changes in surface dipole moments experience pronounced effects on adsorption and activation energies from changing the properties of the EDL.