Spatially confined radical addition reaction in the sub-nanometer scaled interlayers of electrochemically expanded graphene sheets

Here we report a spatially confined radical addition reaction which occurs in the sub-nanometer scaled interlayers of the expanded graphene sheets during the electrochemical exfoliation processes of graphite. Due to its chemical stability, challenge remains to functionalize graphene simultaneously during the preparation processes. To this, we use tetrachloroaluminate (AlCl) as the co-intercalation anions together with sulfate (SO) for the electrochemical exfoliation of graphite. We revealed the extremely irreversible intercalation of AlCl ions in graphite layers and the generation of C–Cl bonds during electrolysis. Chlorine and oxygen were homogeneously distributed on the basal plane of the obtained graphene, and the controlled functionalization was achieved by tuning the concentration of AlCl anions in the electrolyte solution, indicating the spatially confined chlorine addition reaction occurring between the sub-nanometer interlayers of expanded graphite. Furthermore, the chlorine and oxygen hybrid-substituted graphene exhibited excellent electrocatalytic performance for oxygen reduction reaction. This work demonstrates an innovative radical addition reaction in the confined space at nanometer or subnanometer scale and, meanwhile, provides a direct functionalization of graphene during the electrochemical exfoliation of graphite.