Defect-free graphene is impermeable to gases and liquids [1][2][3][4] but highly permeable to thermal protons [5][6][7][8] . Atomic-scale defects such as vacancies, grain boundaries and Stone-Wales defects are predicted [9][10][11] 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.Despite being a one-atom-thick material, no more than a few gas atoms per hour can permeate through micrometer-sized defect-free graphene membranes, as proven experimentally 3 . Even the smallest ions are blocked by the crystal 4 . These phenomena arise because the dense electron clouds of graphene's crystal lattice impose energy barriers of several eV to incoming molecular and ionic species [9][10][11] , which forbids their permeation under ambient conditions. In contrast, it has been shown experimentally that protons, nuclei of hydrogen atoms, can transport through defect-free graphene relatively easily, overcoming an energy barrier of only ≲1 eV (refs 3-6 ). In this context, theory predicts

Strong electric fields can accelerate molecular dissociation reactions. The phenomenon known as the Wien effect was previously observed using high-voltage electrolysis cells that produced fields of about 107 V m−1, sufficient to accelerate the dissociation of weakly bound molecules (e.g., organics and weak electrolytes). The observation of the Wien effect for the common case of water dissociation (H2O $$\leftrightarrows$$ ⇆ H+ + OH−) has remained elusive. Here we study the dissociation of interfacial water adjacent to proton-permeable graphene electrodes and observe strong acceleration of the reaction in fields reaching above 108 V m−1. The use of graphene electrodes allows measuring the proton currents arising exclusively from the dissociation of interfacial water, while the electric field driving the reaction is monitored through the carrier density induced in graphene by the same field. The observed exponential increase in proton currents is in quantitative agreement with Onsager’s theory. Our results also demonstrate that graphene electrodes can be valuable for the investigation of various interfacial phenomena involving proton transport.