Addition of graphene oxide into graphite toward effective positive electrode for advanced zinc-cerium redox flow battery

The paper first reports the use of a kind of positive electrode material (graphite/graphene-oxide composite) in zinc-cerium redox flow battery (RFB). It exhibits excellent electrochemical performance toward Ce3+/Ce4+ redox couple in zinc-cerium RFB. The material was characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The electrochemical activity of this kind of material to Ce3+/Ce4+ redox reaction was studied with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results showed that the electrochemical performance of the electrode was improved significantly when 2.5 wt% graphene oxide (GO) was added into graphite electrode. The redox peak current of Ce3+/Ce4+ couple on the composite electrode was significantly larger than that on the graphite electrode, and the charge transfer resistance on the composite electrode is also obviously reduced. The enhanced electrochemical activity could be attributed to the presence of plentiful oxygen-containing functional groups on the basal planes and sheet edges of the GO and large specific areas introduced by the GO. The energy efficiency of zinc-cerium RFB using graphite/GO composite as positive electrode is around 76.3 %, which is larger than that using graphite (65.9 %). The excellent results demonstrate that the graphite/GO composite holds great promise in the application of zinc-cerium RFB.