Multi-scale modeling of electrochemical interfaces: New methods and applications to RuO2 surfaces

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The computational simulation of electrochemical interfaces is a key methodology to understand electrochemical processes at a molecular level. Solid/liquid interfaces are subject to significant complexity due to the interplay of electrostatic interactions, charge transfer processes and the formation of an electrical double layer. Considering the intricate structure and dynamical processes at electrochemical interfaces and currently available computational resources, the simulation of realistic models with ab initio electronic structure theory is infeasible. In this project we develop new simulation protocols which combine simulation methods at multiple scales to achieve predictive, yet computationally inexpensive, models of electrochemical reactions at catalyst surfaces.As a prototypical example we focus on the electrochemical water oxidation reaction at RuO2/electrolyte interfaces. RuO2 is one of the most efficient catalysts for the oxygen evolution reaction in electrolyzers, but catalyst morphology and stability at operating conditions are still under debate. The intrinsic multiscale nature of electrochemical processes, which involve fast charge redistribution but also electrolyte diffusion processes at a nanosecond timescale, are addressed by complementary methods combining density functional and classical theories. Based on initial screening of surface structures using surface free energy calculations by ab initio thermodynamics, selected structures are used for the development of quantum/molecular mechanics (QM/MM) and implicit solvation techniques. The implemented methods are validated by experimental data and ab initio molecular dynamics simulations treating all components of a system strictly at the same level of density functional theory. From simulations of RuO2/electrolyte interfaces at open-circuit and operating conditions we address fundamental questions concerning morphology, stability and activity in relation to potential, pH and electrical double layer.