Explicit solvation unveils the mechanism of chlorine evolution on RuO₂(110): an AIMD study

The electrochemical chlorine evolution reaction (CER) serves as the cornerstone of the chlor-alkali industry. Ruthenium dioxide (RuO₂)-based materials represent some of the most widely employed electrodes in industrial processes. A mechanistic understanding of reaction processes at the electrode surface is essential for the rational design and targeted modulation of CER kinetics. Herein, we carried out ab initio molecular dynamics (AIMD) simulations with an explicit liquid-solid interface to unravel the CER mechanism on the RuO₂(110) surface. Surface phase diagram analysis identifies the oxygen-saturated configuration as the thermodynamically stable surface. Compared with the conventional simulation based on a gas-solid model that largely neglects the explicit solvation effect, the explicit aqueous environment reshapes the reaction energetics. Electrochemical chloride adsorption, namely the Volmer step, is facilitated by lowering the free energy barrier to 0.53 eV, whereas the Heyrovsky step to generate Cl₂ is coupled with the desorption of Cl₂ from the surface solvent layer, leading to the generation of kinetically unfavorable solvated Cl₂. Thus, a more positive potential, namely a larger overpotential, is required to drive the CER. In comparison, there is no barrier for the Heyrovsky step without explicit solvation. This study highlights the importance of incorporating explicit solvation in electrochemical simulations, and provides insights for the design of CER catalysts.