Interfacial Water-Mediated Ion Transport through Electrified Graphene Membranes

Abstract Ion transport at charged interfaces in aqueous environments is central to a broad spectrum of electrochemical and biological processes1–8. Conventional strategies for electrostatically modulating interfacial ion transport have focused primarily on direct Coulombic interactions, achieved through chemically introduced surface charges9–14 or externally applied potentials15–21, and are typically based on the assumption that water behaves as a passive dielectric medium. Here, we present a nanofluidic platform based on electronically conductive multilayered reduced graphene oxide membranes that reveals a new mechanism of electrically modulated ion transport, in which interfacial water actively governs transport dynamics. This platform enables continuous ion transport measurements across a wide voltage range of both polarities and uncovers strongly asymmetric and nonlinear behaviours, including up to a thousand-fold enhancement in ambipolar diffusivity under strong negative gating, an effect that is unattainable through conventional electrostatics-driven approaches. Molecular dynamics simulations attribute this phenomenon to voltage-induced reorganisation of interfacial water, which promotes ion clustering and fundamentally reshapes interfacial ion dynamics. Our findings establish interfacial water as a voltage-tuneable mediator of ion transport and demonstrate how coupling electrostatic gating with solvent-mediated interactions can enable new designs for electrically responsive nanofluidic and iontronic systems.