Study on the electrochemical reduction of graphene oxide multilayered films

Full text: The chemical oxidative exfoliation of graphite for the production of graphene oxide (GO) is the most feasible and less expensive way of preparation of graphene-based materials. The as-obtained GO still needs to be reduced in order to restore conjugated bonds and improve its optoelectronic properties. GO reduction can be performed by several routes each of which presenting different efficiencies and disadvantages. The electrochemical reduction is an interesting approach, especially when electrochemical applications are devised. The reduced graphene oxide (RGO) can thus be obtained directly onto the working electrode. However, the mechanisms underlying the electrochemical GO to RGO conversion are still controversial and far from a common sense. In order to give an additional point of view to this subject, we investigated the influence of support electrolyte and potential scan over the cyclic voltammetry reduction of graphene oxide multilayered films prepared under the layer-by-layer (LbL) technique. According to our findings, a few voltammetric cycles (~ 5) in any type of tested electrolytes (KCl, H₂SO₄ , Na₂SO₄ , PBS, NaOH) are sufficient to promote the conversion of GO to RGO. The multilayered films initially pale yellow become dark after reduction. To confirm the reduction, Raman and XPS characterization of samples were performed. Among the tested electrolytes, PBS buffer in either pH 7 or 10 was found to be the most effective in the electrochemical reduction. According to XPS data, this electrolyte enables one to decrease the oxygen functionalities, as measured by the surface atomic ratio of C-O/C-C bonds, from 0.20 in the control multilayer to 0.02 and 0.01 for those reduced in PBS at pH 7 and 10, respectively. The process is slow and is more efficient when the electrodes are cycled at lower scan rates. (author)