Inverse kinetic isotope effect of proton and deuteron permeation through pyridinic N-doped graphene

Graphene is becoming an increasingly popular platform for developing high-efficiency hydrogen isotope sepa-ration technologies operated at room temperature. However, its performance can be strongly affected by con-tributions from atomic defects. Understanding the influence of defects on the hydrogen isotope selectivity of graphene is thus imperative but remains elusive. In this work, we investigated the electrically driven proton/ deuteron permeation through nitrogen-doped graphene membranes with varying N concentrations and config-urations. The results show that N-doping significantly enhances the proton and deuteron permeability of gra-phene (by one order of magnitude). More importantly, deuterons are found to permeate faster through pyridinic N-containing defects than protons, demonstrating a pronounced inverse kinetic isotope effect (KIE) with kH/kD of 0.75. Conversely, pyrrolic N-containing defects exhibit a normal KIE (kH/kD = 1.56). The exclusive contribution of the pyridinic N to the inverse KIE is confirmed by the reversed KIE factor of the pyridinic N-dominated sample subjected to modification. Theoretical calculations indicate that the explicit dependence of KIE on N configu-ration originates from the different leading mechanisms of proton/deuteron permeation through these N-con-taining defects, which is governed by the size and the chemisorption imparted by defects. These findings provide fundamental insights into the correlation between defect characteristics and proton/deuteron transport in gra-phene, and contribute to developing economical hydrogen isotope separation technologies through the defect engineering of graphene.