Graphene oxide (GO) and reduced graphene oxide (rGO), synthesised from GO, has a promising future in fields ranging from electronics to energy technologies[1]. We are investigating rGO as porous air electrodes in lithium-air batteries, which have potential to reach energy densities many times higher than for present day batteries. Small changes in the GO synthesis affects properties such as intercalated water[2] and surface functionalities[3], and changes in the thermal reduction routes causes changes in the deoxygenation process[4]. The synthesis mechanism of GO by the modified Hummers method and subsequent controlled thermal reduction to produce rGO is still unknown. We present the in situ synchrotron X-ray diffraction (XRD) of the two syntheses.

The in situ XRD of the GO synthesis, showed that the reaction proceeds in three separate stages, with formation of GO starting early during the synthesis. The first stage was the dissolution of potassium permanganate, followed by an intercalation stage and subsequent formation of crystalline material. The in situ XRD results of the thermal reduction of GO to rGO show a dependence on the temperature ramping and addition of diamond powder. Three stages were also observed for the reduction process; a GO stage, an amorphous stage and formation of a graphitic like material. The results show how the nature of the rGO material depends heavily on both temperature and additives. The three stages observed for both syntheses illuminates how important it is to consider the experimental parameters dependent on the application; they might even have to be optimized separately.

[1] M. Segal, Nat Nano, 4 (2009) 612-614.
[2] T.N. Blanton, D. Majumdar, Powder Diff., 27 (2012) 104-107.
[3] M.M. Storm, M. Overgaard, R. Younesi, N.E.A. Reeler, T. Vosch, U.G. Nielsen, K. Edström, P. Norby, Carbon, (2014, submitted).
[4] A. Ganguly, S. Sharma, P. Papakonstantinou, J. Hamilton, The Journal of Physical Chemistry C, 115 (2011) 17009-17019.

Mie Møller Storm is a Ph.D. student at the Energy Conversion department at The Technical University of Denmark, where she is studying cathodes for Li-air batteries with primary focus on different graphene materials and in situ X-ray diffraction studies of capillary batteries.