Perfect proton selectivity in ion transport through two-dimensional crystals.

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Defect-free 2D materials like graphene and hexagonal boron nitride are impermeable to gases but permeable to protons.
• The permeation of small ions through these materials remains largely untested.

Purpose of the Study:

• To investigate the permeation of small ions through defect-free graphene and hexagonal boron nitride monolayers.
• To determine if these 2D materials exhibit selective ion transport.

Main Methods:

• Mechanically exfoliated graphene and hexagonal boron nitride monolayers were used.
• Suspended monolayers were tested for atomic-scale defects using gas permeation.
• Monolayers separated reservoirs of hydrochloric acid solutions to measure ion flow and electrical current.

Main Results:

• Graphene and hexagonal boron nitride exhibited perfect Nernst selectivity, allowing only proton permeation.
• No detectable flow of counterions (chloride ions) was observed.
• Protons accounted for all measured electrical current, confirming their selective passage.

Conclusions:

• Defect-free 2D materials like graphene and hexagonal boron nitride are highly selective for proton transport.
• These findings support the conclusion that thermal protons can penetrate defect-free 2D crystals.
• The results have implications for developing advanced separation technologies utilizing 2D materials.