Electrochemical Electron Transfer: Key Concepts, Theories, and Parameterization via Atomistic Simulations.

Electron transfer (ET) at electrochemical interfaces lies at the heart of numerous modern technologies, yet its theoretical description and computational modeling remain dynamic areas of research. This review is aimed at elucidating the key concepts and theories of ET kinetics, focusing on the coupling between classical solvent fluctuations and quantum electronic states of metallic electrodes and redox species. We begin with fundamental rate theories, reaction coordinates, and time scales relevant to electrochemical systems, and then systematically explore the regimes of weak, strong, and intermediate electronic coupling. Special attention is given to solvent dynamics and the structure of the electrical double layer (EDL), both of which critically impact ET kinetics. Atomistic simulations, particularly density functional theory (DFT) and molecular dynamics (MD), are highlighted as useful tools for assessing key assumptions such as linear response and determining key parameters such as solvent reorganization energy, electronic coupling strength, and those describing nuclear dynamics. We conclude by outlining opportunities for advancing the field through multiscale, quantum-classical models that incorporate EDL effects, multiple reaction coordinates, solvent-controlled dynamics, and transitions between adiabatic and nonadiabatic regimes. This review aims to serve as both a conceptual guide and a practical resource for researchers seeking to integrate theory and simulation in the study of electrochemical ET across diverse systems.