Electrochemistry at solid-water interface lies at the center of many technologies to address energy and environment challenges. Although Density Functional Theory (DFT) has been widely used to study such system, these calculations are often based on simplified models that neglect the presence and/or dynamics of surface charge and solvation, which fluctuate at a given reaction coordinate and evolve along the reaction path. Consequently, these models fail to give accurate/correct kinetic information about the electrochemical reactions at solid-water interface.<br/><br/>Here we develop a new first-principles model that overcomes these challenges and thus enables accurate and efficient simulations of the reaction kinetics at the electrified solid-water interface. Specifically, we use sufficient number of water molecules in conjunction with implicit solvation model to fully solvate the relevant chemical species, and couple the electrons with a fictitious potentiostat so that the number of electrons fluctuates following the grand-canonical distribution at the preset electrode potential. To accelerate the sampling of the configurations and charge states, we use molecular dynamics with the force field generated from on-the-fly machine learning of DFT results. To obtain the free energy barriers, we use the thermodynamic integration to compute the free energy profiles along the reaction coordinates.<br/><br/>We then apply this model to study two important systems: (1) CO2 reduction to CO catalyzed by single-nickel-atom embedded in graphene. It has high activity and selectivity in experiments, but the active site structure and the mechanism are under debate; (2) Oxygen reduction to hydrogen peroxide by carbon catalysts. It has high performance at base conditions but poor performance at acid conditions, but the origin of this pH dependence is unclear. Our model is able to explain both systems, and reveals the critical roles of charge capacity and hydrogen bonding in single metal atom electrocatalysis.

First-principles simulations of the electrochemical kinetics at solid-water interface

ACS Spring Meeting 2021

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