Toward rational understanding of the hydrogen evolution polarization curves through multiscale simulations.

To properly understand complex heterogeneous electrocatalytic processes, it is essential to consider not only the microscopic electrochemical reaction mechanisms at electrodes but also the macroscopic mass transport effects, which are usually overlooked in current computational electrochemistry. Here, we develop a multiscale simulation framework that integrates grand canonical density functional theory calculations, microkinetic modeling, and a continuum transport model to successfully reproduce the experimental polarization curves of hydrogen evolution reaction on Au(111) across the entire pH range. Our simulations reveal how the potential-dependent evolution of local environments governs reaction mechanisms and behavior, identifying a dynamic balance between local pH increases and decreases in reaction barriers that controls characteristic current plateaus. By classifying polarization curves into five distinct regimes based on their governing factors, we provide comprehensive mechanistic insights into how mass transport influences polarization behavior. Our multiscale simulation framework not only adequately reproduces existing experimental results but also provides a basis for rational optimization of the microenvironment to achieve efficient electrochemical processes.