Exploration of the Effective Location of Surface Oxygen Defects in Graphene-Based Electrocatalysts for All-Vanadium Redox-Flow Batteries

Oxygen functional groups play a key role in vanadium redox reactions. To identify the effective location of oxygen functionalities in graphene-based nanomaterials, a selectively edge-functionalized graphene nanoplatelet (E-GnP) with a crystalline basal plane is produced by a ball-milling process in the presence of dry ice. For comparison, the reduced graphene oxide (rGO) that contains defects at both edges and in the basal plane is produced by a modified Hummers' method. The location of defects in the graphene-based nanomaterials significantly affects the electrocatalytic activity towards vanadium redox couples (V2+/V3+ and VO2+/VO2 (+)). The improved activity of these nanoplatelets lies in the presence of oxygen defects at the edge sites and higher crystallinity of basal planes than in rGO. This effective location of oxygen defects facilitates fast electron-transfer and mass-transport processes.