Proton and Li-Ion Permeation through Graphene with Eight-Atom-Ring Defects

TL;DR

Disordered graphene with high densities of 8-atom-ring defects significantly increases proton and lithium ion permeability while still blocking larger molecules, offering potential for advanced membrane and barrier applications.

Contribution

This study experimentally demonstrates that atomic-scale defects in graphene dramatically enhance proton and lithium ion permeation, a phenomenon previously only predicted theoretically.

Findings

Proton permeability increases by ~1,000 times in defect-rich graphene.

Lithium ions can permeate through disordered graphene.

Larger molecules remain blocked despite defects.

Abstract

Defect-free graphene is impermeable to gases and liquids but highly permeable to thermal protons. Atomic-scale defects such as vacancies, grain boundaries and Stone-Wales defects are predicted to enhance graphene's proton permeability and may even allow small ions through, whereas larger species such as gas molecules should remain blocked. These expectations have so far remained untested in experiment. Here we show that atomically thin carbon films with a high density of atomic-scale defects continue blocking all molecular transport, but their proton permeability becomes ~1,000 times higher than that of defect-free graphene. Lithium ions can also permeate through such disordered graphene. The enhanced proton and ion permeability is attributed to a high density of 8-carbon-atom rings. The latter pose approximately twice lower energy barriers for incoming protons compared to the 6-atom rings of graphene and a relatively low barrier of ~0.6 eV for Li ions. Our findings suggest that disordered graphene could be of interest as membranes and protective barriers in various Li-ion and hydrogen technologies.