Microscopic dynamics of charge separation at the aqueous electrochemical interface

Abstract

We have used molecular simulation and methods of importance sampling to study the thermodynamics and kinetics of ionic charge separation at a liquid water-metal interface. We have considered this process using canonical examples of two different classes of ions: a simple alkali-halide pair, Na${}^{+}$I${}^{-}$, or classical ions, and the products of water autoionization, H${}_3$O${}^{+}$OH${}^{-}$, or water ions. We find that for both ion classes, the microscopic mechanism of charge separation, including water's collective role in the process, is conserved between the bulk liquid and the electrode interface. Despite this, the thermodynamic and kinetic details of the process differ between these two environments in a way that depends on ion type. In the case of the classical ion pairs, a higher free energy barrier to charge separation and a smaller flux over that barrier at the interface, results in a rate of dissociation that is 40x slower relative to the bulk. For water ions, a slightly higher free energy barrier is offset by a higher flux over the barrier from longer lived hydrogen bonding patters at the interface, resulting in a rate of association that is similar both at and away from the interface. We find that these differences in rates and stabilities of charge separation are due to the altered ability of water to solvate and reorganize in the vicinity of the metal interface.

arXiv comment6 pages, 3 figures + SI

References in corpus (8)

• A molecular perspective of water at metal interfaces
• Joint Density-Functional Theory of the Electrode-Electrolyte Interface: Application to Fixed Electrode Potentials, Interfacial Capacitances, and Potentials of Zero Charge
• Solvation at Aqueous Metal Electrodes
• Charge fluctuations in nano-scale capacitors
• Water at an electrochemical interface - a simulation study
• The statistics of electric field fluctuations in liquid water
• Molecular Dynamics Simulation of Water between Metal Walls under Electric Field: Dielectric Response and Dynamics after Field Reversal
• Fluctuations of local electric field and dipole moments in water between metal walls

Cited by in corpus (8)

• Molecular Simulation of Electrode-Solution Interfaces
• Water's interfacial hydrogen bonding structure reveals the effective strength of surface-water interactions
• Local distortions and dynamics in hydrated Y-doped BaZrO${}_3$
• Microscopic origin of the effect of substrate metallicity on interfacial free energies
• Studying rare nonadiabatic dynamics with transition path sampling quantum jump trajectories
• Rate constants in spatially inhomogeneous systems
• Learning intermolecular forces at liquid-vapor interfaces
• Deep vacancy induced low-density fluxional interfacial water