Anomalous Proton Blocking Property of Pore‐Free Graphene Oxide Membrane

Graphene oxide (GO) has been attracting intensive attention as a flexible barrier film, however, provides no barrier for proton transfer due to its out-of-plane proton conductivity (10^-6 S cm^-1) based on nanoscale defects with oxygen functional groups. In this study, it is reported that a pore-free GO (Pf-GO) membrane with controlled oxygen functional groups exhibits unexpected proton blocking behavior (10^-11 S cm^-1). Proton permeation tests conducted in aqueous solution demonstrate that proton permeation is below the detection limit, and lithium metal foils coated with the Pf-GO show higher chemical stability to water than those coated with previously reported GO. The Pf-GO has periodic honeycomb atomic structure, which is found to impart the Pf-GO membrane with novel performance characteristics distinct from those of conventional GO.