Oxygen functional groups improve the energy storage performances of graphene electrochemical supercapacitors

Graphene is a promising electrode material for supercapacitors due to its superior physical and chemical properties, but the influence of its oxygen functional groups on capacitive performance still remains somewhat uncertain. In this work, graphene sheets with different oxygen content have been prepared through thermal reduction in argon. Furthermore, oxidation and pore-forming treatment of graphene annealed at 800 °C are also performed to explore the important effect of oxygen functional groups. The effects of disorder degree, surface area and oxygen functional groups on the specific capacitance were explored systematically. The content and species of oxygen functional groups are found to be significant factors influencing the electrochemical supercapacitor performance of graphene electrodes. The specific capacitances of graphene annealed at 200, 400 and 800 °C are 201, 153 and 34 F g^-1, respectively. However, the specific capacitance of graphene reduced at 800 °C can be increased to 137 F g^-1 after nitric acid oxidation treatment, and is only 39 F g^-1 after pore forming on graphene surface, demonstrating that the oxygen functional groups can improve the capacitive performances of graphene electrochemical supercapacitors.