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

Area of Science:

• Materials Science
• Physical Chemistry
• Nanotechnology

Background:

• Ion transport in nanoconfinement (<2 nm) is complex and differs from bulk behavior.
• Surface charge and applied potentials create electric fields influencing ion diffusion within nanoporous materials.
• The electrical double layer (EDL) under nanoconfinement significantly impacts ion dynamics, posing experimental challenges.

Purpose of the Study:

• To experimentally investigate how surface potential and nanoconfinement interplay to manipulate ion diffusion.
• To explore the use of tunable nanoconfinement in graphene-based membranes for controlling ion transport.
• To understand the mechanisms behind potential-induced modulation of ion diffusion.

Main Methods:

• Utilized layered graphene-based nanoporous membranes with tunable nanoconfinement.
• Applied controlled surface potentials to modulate the electrical double layer (EDL).
• Measured ion diffusion rates across a range of salt concentrations, including up to seawater salinity.

Main Results:

• Demonstrated strong modulation of sub-2 nm confined ion diffusion by surface potential-induced EDL.
• Observed reversible modulation and anomalous enhancement of diffusion rates (4-7 times) within 0.5 V.
• Showcased the influence of potential sign, ion pair combination, and concentration on diffusion.

Conclusions:

• Surface potential is a critical factor in controlling ion diffusion in severely confined systems.
• Anomalous diffusion enhancement is attributed to strong ion-ion correlations under nanoconfinement, beyond conventional theories.
• Graphene-based nanoporous membranes offer a promising platform for tunable ion transport control in energy and water applications.