Proton transport through one atom thick crystals

TL;DR

This study reveals that atomically thin graphene and hBN monolayers are unexpectedly permeable to protons under ambient conditions, challenging prior assumptions of their impermeability and opening new avenues for hydrogen technologies.

Contribution

It demonstrates proton transport through graphene and hBN monolayers, showing their potential as atomically thin proton conductors, which was previously thought impossible.

Findings

Graphene and hBN monolayers are permeable to protons at room temperature.

Proton conductivity is highest in hBN with low activation energy (~0.3 eV).

Graphene's proton conductivity improves at higher temperatures, below 10^-3 Ohm/cm^2 above 250°C.

Abstract

Graphene is impermeable to all gases and liquids, and even such a small atom as hydrogen is not expected to penetrate through graphene's dense electronic cloud within billions of years. Here we show that monolayers of graphene and hexagonal boron nitride (hBN) are unexpectedly permeable to thermal protons, hydrogen ions under ambient conditions. As a reference, no proton transport could be detected for a monolayer of molybdenum disulfide, bilayer graphene or multilayer hBN. At room temperature, monolayer hBN exhibits the highest proton conductivity with a low activation energy of about 0.3 eV but graphene becomes a better conductor at elevated temperatures such that its resistivity to proton flow is estimated to fall below 10^-3 Ohm per cm2 above 250 C. The proton barriers can be further reduced by decorating monolayers with catalytic nanoparticles. These atomically thin proton conductors could be of interest for many hydrogen-based technologies.