Residual oxygen groups in nitrogen-doped graphene to enhance the capacitive performance

Abstract

Nitrogen-doped graphene (NG) was obtained from a facile and eco-friendly hydrothermal reaction and used as electrode materials for supercapacitors. The textural and chemical properties could be easily tuned by adjusting the basicity of the reaction environment. As the basic reaction conditions became stronger, the sheets of NG tended to stack together, the content of residual oxygen groups increased, but the nitrogen content decreased, which affected the electrochemical performance. The NG synthesized under a weak basic environment shows great pseudocapacitance and the largest electrochemical performance in a 6 mol L⁻¹ KOH aqueous electrolyte when measured in a three-electrode system, which can be attributed to its randomly distributed and loosely stacked structure and high amount of residual oxygen atoms (12.8 at%). Furthermore, it presented excellent cycling stability with a capacitance retention ratio of 92.86% at the current densities of 5 A g⁻¹ after 10 000 charge–discharge cycles in two-electrode configuration, which kept stable after 5000 cycles. These results implied that the NG sheets obtained by this simple eco-friendly approach are suitable for high performance supercapacitor applications.