Beyond Dielectrics: Interfacial Water Polarization Governs Graphene-Based Electrochemical Interfaces

TL;DR

This study demonstrates that interfacial water polarization significantly influences electrochemical interfaces on graphene, challenging the traditional dielectric assumption and leading to a revised electric double layer model.

Contribution

It introduces a new understanding of interfacial water polarization effects, extending beyond classic models to include surface-induced polarization impacts.

Findings

Interfacial water polarization differs from bulk water.

Surface polarization can invert electrode potential polarity.

Revised EDL model better describes interfacial electrostatics.

Abstract

Water molecules are traditionally regarded as passive dielectric media in electrochemical systems. In this work, we challenge this conventional perspective using molecular dynamics simulations and theoretical analysis. We show that interfacial water is polarized differently from bulk water and effectively screens the electrostatic potential between ions and the surface. This goes beyond the classic electric double layer (EDL) model, which treated water as merely a passive dielectric. The observed overscreening occurs because a significant portion of water polarization directly responds to the graphene surface, in addition to screening the electrostatic interactions between ions and charged surfaces. Furthermore, we reveal that this surface-induced polarization of interfacial water governs the electric potential distribution and EDL capacitance, and can even invert the electrode surface potential polarity, overriding the contribution of ions. These molecular-level insights lead to a revised EDL model that more accurately describes the electric and chemical potential distributions in the interfacial EDL regions.