Water Structure, Dynamics, and Sum-Frequency Generation Spectra at Electrified Graphene Interfaces

Abstract

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Confined Water’s Dielectric Constant Reduction Is Due to the Surrounding Low Dielectric Media and Not to Interfacial Molecular Ordering

“…5,7,23,25 A second difficulty for this postulate is that it would require an extreme alignment of interfacial water dipoles, a situation in stark contrast with the moderate structural perturbation of water at graphene interfaces found in a series of recent molecular dynamics simulations. [26][27][28][29] Also, it has been proposed 16 that the slower reorientation dynamics of water at the interface compared to the bulk would be consistent with the very low dielectric constant. However, the static dielectric constant is not a dynamical property, and in any event our recent work has shown 26,27 that interfacial water dynamics is too moderately affected to be consistent with any extreme restriction of molecular orientations.…”

“…[26][27][28][29] Also, it has been proposed 16 that the slower reorientation dynamics of water at the interface compared to the bulk would be consistent with the very low dielectric constant. However, the static dielectric constant is not a dynamical property, and in any event our recent work has shown 26,27 that interfacial water dynamics is too moderately affected to be consistent with any extreme restriction of molecular orientations. 30 To address the dielectric constant issue, we will use molecular dynamics simulations of water confined between graphene plates with different separations.…”

Stripping off of the Hydration Shells in the Double Layer Formation: Water Networks Matter

“…Furthermore, our results on the in-plane orientation of water that persists longer under positive surface charging supports the idea of an asymmetric reorientation of water at positive/negative electrodes as described in Refs. (13,49). The novel result provided here is that the building-up of an in-plane oriented interfacial layer exclusively at positively charged gold surfaces causes anions and cations to migrate differently when positive/negative potentials are applied.…”

A Model Electron Transfer Reaction in Confined Aqueous Solution

“…There is zero charge placed on the graphene carbon atoms (see Refs. [18,19] for the distinct situation of graphene electrodes held at constant potential and the impact on interfacial water layer structure and dynamics). The simulation box dimensions are 24.58 × 25.56 × 62 Å 3 and the number of water molecules ( 1150) is determined such that the water has the correct bulk density in the middle of the slab.…”

“…[13] In the present work, we explore such a possibility for key aspects of a model ET reaction in water bounded by (here uncharged) graphene sheets, whose separation is fixed, a system of considerable interest in a wide variety of arenas. [14][15][16][17] Our study employs both molecular dynamics simulations and the theoretical results of previous efforts [12,18,19] on water confined between such sheets, in particular a recent investigation [12] of water's dielectric constant behavior in such an environment.…”