  Defect-free graphene is impermeable to gases and liquids but highly permeable
to thermal protons. Atomic-scale defects such as vacancies, grain boundaries
and Stone-Wales defects are predicted to enhance graphene's proton permeability
and may even allow small ions through, whereas larger species such as gas
molecules should remain blocked. These expectations have so far remained
untested in experiment. Here we show that atomically thin carbon films with a
high density of atomic-scale defects continue blocking all molecular transport,
but their proton permeability becomes ~1,000 times higher than that of
defect-free graphene. Lithium ions can also permeate through such disordered
graphene. The enhanced proton and ion permeability is attributed to a high
density of 8-carbon-atom rings. The latter pose approximately twice lower
energy barriers for incoming protons compared to the 6-atom rings of graphene
and a relatively low barrier of ~0.6 eV for Li ions. Our findings suggest that
disordered graphene could be of interest as membranes and protective barriers
in various Li-ion and hydrogen technologies.

Materials Science;Mesoscale and Nanoscale Physics