Graphene quantum dots cut from graphene flakes: high electrocatalytic activity for oxygen reduction and low cytotoxicity

3-8 nm sized high quality graphene quantum dots with zigzag edges and multi-heteroatom doping were synthesized through a green process of electrochemically cutting pristine few-layer graphene flakes. The graphene quantum dots exhibit the structural features of monodisperse and shaped nanocrystals codoped by O, N and F elements or chemical groups mainly at the zigzag edges. The cutting and in situ doping of the graphene flakes into dots were realized in the potential/current exchangeable electrochemical etching process without any thermal treatment. It was found that the graphene dots showed high electrocatalytic activity for the oxygen reduction reaction including 70 times enhancement in voltammetric current in oxygen saturated KOH compared to that in nitrogen. In addition, low in vitro cytotoxicity and fluorescent labeling to Vero cells and NRK cells of the graphene dots were presented. The Gdots synthesized may potentially be applied in the fields of electrocatalysis and biomedicine.