Buffering agents-assisted synthesis of nitrogen-doped graphene with oxygen-rich functional groups for enhanced electrochemical performance

Abstract In this work, designed growth of two type of N-doped graphene nanosheets has been investigated using NH 4 H 2 PO 4 and (NH 4 )2HPO 4 as buffering agents, respectively, in a mild hydrothermal process. X-ray photoelectron spectroscopy (XPS) characterization indicates that the graphene nanosheets grown using NH 4 H 2 PO 4 (NGC) have lower nitrogen but higher oxygen content than those using (NH4)2HPO4 (NGL). Electrochemical measurements in three-electrode systems show that both type of the graphene products exhibit superior electrochemical performance (383 and 356 F g-1 at 1 A g-1). While the specific capacitance of NGC is steadily higher than that of NGL under all investigated current densities, the capacitance attenuation of NGL is 4.80% from 500 to 10000 cycles showing more durable in cyclicity than that of NGC (8.81%). The two-electrode supercapacitor devices for NGC and NGL exhibit high energy density of 12.21 Wh kg −1 and 9.28 Wh kg −1 at 0.25 A g −1 . The difference in electrochemical behaviors between NGC and NGL electrodes can be attributed to the different contribution of nitrogen and oxygenic groups. The buffer agents assisted synthesis procedure coupled with the reasonable capacitance performance suggests an alternative way in the designed functionalization of graphene for developing high performance supercapacitors.