Proton and molecular permeation through the basal plane of monolayer graphene oxide

TL;DR

This study reveals that monolayer graphene oxide is impermeable to gases like helium but allows highly efficient proton transport across its basal plane, surpassing graphene in proton conductivity, with implications for membrane technology.

Contribution

It demonstrates that large-area monolayer GO is gas-impermeable yet highly proton-conductive, challenging assumptions about nanoscale pinholes and highlighting functionalization potential.

Findings

GO monolayers are gas-impermeable over large areas

Proton conductivity in GO is nearly 100 times higher than in graphene

Chemical functionalization can enhance proton transport without gas leakage

Abstract

Two-dimensional (2D) materials offer a prospect of membranes that combine negligible gas permeability with high proton conductivity and could outperform the existing proton exchange membranes used in various applications including fuel cells. Graphene oxide (GO), a well-known 2D material, facilitates rapid proton transport along its basal plane but proton conductivity across it remains unknown. It is also often presumed that individual GO monolayers contain a large density of nanoscale pinholes that lead to considerable gas leakage across the GO basal plane. Here we show that relatively large, micrometer-scale areas of monolayer GO are impermeable to gases, including helium, while exhibiting proton conductivity through the basal plane which is nearly two orders of magnitude higher than that of graphene. These findings provide insights into the key properties of GO and demonstrate that chemical functionalization of 2D crystals can be utilized to enhance their proton transparency without compromising gas impermeability.