Abstract
This study investigated the electrochemical activities of various chemical reduced Graphenes for electrode in all-vanadium redox flow battery (VRB) .The reductants used including NaBH4,N2H4, and HBr. The XPS analysis was utilized to analyze the element compositions of the Graphene oxide, HBr reduced Graphene, NaBH4 reduced Graphene, and N2H4 reduced Graphene. The oxygen functional groups in Graphene is related to the electrochemical activity. The correlation between oxygen functional groups and electrochemical activity in VRB was studied in detail. The electrochemical activities of graphene prepared with various redox reactions of [VO2]+/[VO]2+ were studied by cyclic voltammetry. Results showed that HBr reduced Graphene exhibited the highest electrochemical activity ( the smallest peak potential separation is 0.26V, 0.28V and 0.32V for NaBH4 reduced Graphene and N2H4 reduced Graphene,respectively.)due to the balance between electroactivity and electrical conductivity of the HBr reduced Graphene. The EIS results show that the Y value of HBr reduced Graphene(9.3×10-5S.s-n) is higher than other graphenes respectively, 2.57×10-5S.s-n and 1.31×10-5 S.s-n for NaBH4 and N2H4 reduced graphene, respectively, implying that Vanadium ions adsorbed on the HBr reduced graphene electrode surface are easier than other graphenes.The easier the Vanadium ions adsorbed on the electrode, the higher the electrochemical activity. Consequently, HBr reduced graphene eletrode shows the highest electrochemical activity among various chemical reduced Graphenes.