Formation of graphite oxide nano-disks by electrochemical oxidation of HOPG

•Nano-disks of graphite oxide is formed on the HOPG surface by electroxidation.•They are 15 nm in diameter, an electrical insulator, and surface-bound material.•They are different from the conventional view of the intercalation.

When HOPG (highly oriented pyrolytic graphite) was electrochemically oxidized in alkali solution, STM observation showed that graphite oxide with homo-sized disks 15 nm in diameter and 0.5 nm in thickness was formed dispersively on the HOPG surface. With an increase in the anodic charge, the number of the disks enhanced, and covered finally the HOPG surface without overlap at the maximum coverage, 70%. The projected area of the disks was proportional to the anodic charge when the charge was small. The disks were hydrophilic. The double layer capacitance of the oxidized HOPG increased slightly with the anodic charge, implying that the disks should be an electrical insulator. The fully disk-coated HOPG did not block the diffusion-controlled current of the redox species. The layer of the disks must be porous for ions or solutions. The formation of the uniform size may be ascribed to the difference between the density of graphite oxide and that of the basal plane of graphite. The formation of nano-disks and their properties are inconsistent with such an image of intercalation that ions are inserted into layers of graphenes of HOPG.

Graphical abstractSTM image of the HOPG surface oxidized at 1.2 V, which includes some nano-disks on the crystalline graphite.Figure optionsDownload full-size imageDownload as PowerPoint slide