Low-voltage electrostatic modulation of ion diffusion through layered graphene-based nanoporous membranes

Abstract

Ion transport in nanoconfinement differs from that in bulk and has been extensively researched across scientific and engineering disciplines. For many energy and water applications of nanoporous materials, concentration-driven ion diffusion is simultaneously subjected to a local electric field arising from surface charge or an externally applied potential. Due to the uniquely crowded intermolecular forces under severe nanoconfinement (<2 nm), the transport behaviours of ions can be influenced by the interfacial electrical double layer (EDL) induced by a surface potential, with complex implications, engendering unusual ion dynamics. However, it remains an experimental challenge to investigate how such a surface potential and its coupling with nanoconfinement manipulate ion diffusion. Here, we exploit the tunable nanoconfinement in layered graphene-based nanoporous membranes to show that sub-2 nm confined ion diffusion can be strongly modulated by the surface potential-induced EDL. Depending on the potential sign, the combination and concentration of ion pairs, diffusion rates can be reversibly modulated and anomalously enhanced by 4~7 times within 0.5 volts, across a salt concentration gradient up to seawater salinity. Modelling suggests that this anomalously enhanced diffusion is related to the strong ion-ion correlations under severe nanoconfinement, and cannot be explained by conventional theoretical predictions.

Solvation‐Involved Nanoionics: New Opportunities from 2D Nanomaterial Laminar Membranes

“…Although nanopores may only be able to accommodate one or two ionic layers where this overscreening effect could be prevented, the short‐range ion–ion correlation may still affect the transport of ions in nanopores . It has recently been found that ion–ion correlation could also account for the ability of electrostatic modulation of ion diffusion in graphene‐based nanochannels of less than 2 nm …”

“…Examples of this approach include chemical functionalization and thermal annealing . Additionally, the electrons inside the materials can be modulated by the means of voltage bias or light illumination so that the electrostatic interactions (e.g., Debye screening in EDL) between ions and materials could be indirectly regulated through the coupling of electrons and ions . Examples of materials with such functionality include graphene and MoS 2 , where metal‐semiconductor transition for modulation of electrons could be achieved by controlling the reduction level or phase transition .…”

Structure and Transport Properties of Water and Hydrated Ions in Nano‐Confined Channels

“…Surprisingly, two distinct peaks of the counter-ions will be observed with a surface charge density of −0.2882 C m −2 . [150] Generally, diffusion phenomena are mainly divided into two types, namely, the diffusion caused by the concentration gradient and self-diffusion by the heat movement. [146][147][148] This can be explained that one layer of counter-ions is dehydrated and adsorbed onto the negatively charged solid wall under high surface charge density, which forms the inner Helmholtz plane.…”

Self‐Assembled Gold Arrays That Allow Rectification by Nanoscale Selectivity

“…[17,18] Theasymmetric shapes and charge distributions of nanochannels contribute to the generation of their rectification characteristics. [19] Nanochannels with rectifying characteristics can be roughly divided into two types:h omogeneous structures [20] and heterostructures. [21,22] In general, stimulusresponsive gating, such as pH gating [23][24][25] and light-responsive gating, [26][27][28] can be achieved by the functional modification of the inner surface of the nanochannel.…”