Electrocatalysis is pivotal in sustainable energy infrastructure, enabling processes like green hydrogen production and CO₂ conversion using renewable energy. 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 accurately represent reactions but are limited by the cost of modeling the dynamics within the electrochemical double-layer (EDL). Representing elementary electrochemical reaction paths and activation barriers especially challenging due to coupled 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 across multiple metals. DFT calculations capture the local electronic structure of adsorbates on electrocatalysts. The DDEC method is used to assign adsorbate and transition state’s atomic charges. The DFT-located state is then integrated into an FF-MD model of the EDL, incorporating complex solvation effects and ion distribution in a fully electrified model. A classical dynamic charge approach ("QDyn") classically simulates metal charge movement in response to electrolyte dynamics, enabling simulations of nanoseconds over modest computational resources. The ion distributions produced by this classical method were parameterized against umbrella sampled ab-initio MD simulations, demonstrating consistency with higher-accuracy methods. DFT-optimized structures are inserted into FF-MD simulations to examine solvation energy changes along reaction paths. This analysis assesses activation barriers as a function of electrode potential and EDL structure. Our model predicts that processes with large surface dipole changes show significant adsorption and activation energy shifts due to EDL property variations.
