Abnormally selective proton transport through angstrom channels of highly reduced graphene oxide

The fabrication of advanced membranes with simultaneously high electron and proton conductivities for energy applications such as H₂ separation has been a long-running challenge because a trade-off exists between the two conductivities in general. Here, we report simultaneous improvement of the electron and proton conductivities in angstrom scale graphene oxide (GO) channels through elaborate thermal reduction and vertical confinement of the stacked GO. The electrical conductivity in the highly reduced GO angstrom channels is significantly improved by the removal of oxygen functional groups, which cause high resistance. Concurrently, the extremely reduced channel size of 4.4 Å allows protons to selectively pass through while easily removing other ions through the sieving mechanism. The GO angstrom channels reduced at 220 °C show 58.8 times higher selectivity for protons compared to K⁺ ions in a 1 M KCl environment, indicating a 42.6-fold improvement over the selectivity of Nafion. The highly reduced horizontal GO membrane has potential applicability in energy devices based on proton exchange membrane requiring high electron as well as proton conductivities.