Entropy Effects on Reactive Processes at Metal-Solvent Interfaces

Obtaining a reliable estimate of the reaction entropy is of utmost importance for the proper prediction of the reaction-free energies of chemical transformations at electrochemical interfaces. In this realm, we demonstrate the suitability of the two-phase thermodynamic (2PT) model and classical molecular dynamics simulations for the accurate and computationally efficient determination of the entropies of reactive species in a solvent environment. We present a systematic analysis of the entropies of different alcohol species in bulk solution and at platinum (Pt), silver (Ag), and lead (Pb) surfaces. The key observation is a metal-specific entropy reduction at metal-water interfaces in comparison to the corresponding entropy values obtained for bulk aqueous solvents. Entropies are seen to decrease by at least 15% relative to the bulk environment. This effect is attributed to the reduction in rotational and translational entropy contributions. By comparison of these results with predictions of theoretical models, the origin of the cavitation entropy is revealed. Overall, we demonstrate that solvation effects exert a significant impact on the free energies of adsorption/desorption and CO2 reaction-free energies that can cause changes of several orders of magnitude in reaction rates. Entropic effects are therefore highly relevant for the deciphering of electrochemical processes.