Measuring the Proton Selectivity of Graphene Membranes

TL;DR

This study investigates proton transport through graphene membranes, revealing that defects facilitate proton passage and that defect modification can tune selectivity, providing insights for membrane design.

Contribution

It demonstrates that proton selectivity in graphene membranes is primarily due to defects and shows how defect engineering can enhance selectivity.

Findings

Protons pass through defects in graphene membranes.

Blocking defects reduces ionic current but increases proton selectivity.

CVD-grown graphene is only weakly selective for protons.

Abstract

By systematically studying the proton selectivity of free-standing graphene membranes in aqueous solutions we demonstrate that protons are transported by passing through defects. We study the current-voltage characteristics of single-layer graphene grown by chemical vapour deposition (CVD) when a concentration gradient of HCl exists across it. Our measurements can unambiguously determine that H+ ions are responsible for the selective part of the ionic current. By comparing the observed reversal potentials with positive and negative controls we demonstrate that the as-grown graphene is only weakly selective for protons. We use atomic layer deposition to block most of the defects in our CVD graphene. Our results show that a reduction in defect size decreases the ionic current but increases proton selectivity.