Control of proton transport and hydrogenation in double-gated graphene.

Abstract

The basal plane of graphene can function as a selective barrier that is permeable to protons^1,2 but impermeable to all ions^3,4 and gases^5,6, stimulating its use in applications such as membranes^1,2,7,8, catalysis^9,10 and isotope separation^11,12. Protons can chemically adsorb on graphene and hydrogenate it^13,14, inducing a conductor-insulator transition that has been explored intensively in graphene electronic devices^13-17. However, both processes face energy barriers^1,12,18 and various strategies have been proposed to accelerate proton transport, for example by introducing vacancies^4,7,8, incorporating catalytic metals^1,19 or chemically functionalizing the lattice^18,20. But these techniques can compromise other properties, such as ion selectivity^21,22 or mechanical stability²³. Here we show that independent control of the electric field, E, at around 1 V nm^-1, and charge-carrier density, n, at around 1 × 10¹⁴ cm^-2, in double-gated graphene allows the decoupling of proton transport from lattice hydrogenation and can thereby accelerate proton transport such that it approaches the limiting electrolyte current for our devices. Proton transport and hydrogenation can be driven selectively with precision and robustness, enabling proton-based logic and memory graphene devices that have on-off ratios spanning orders of magnitude. Our results show that field effects can accelerate and decouple electrochemical processes in double-gated 2D crystals and demonstrate the possibility of mapping such processes as a function of E and n, which is a new technique for the study of 2D electrode-electrolyte interfaces.