Synthesis and characterization of nitrogen-doped graphene hydrogels by hydrothermal route with urea as reducing-doping agents

Abstract

Nitrogen-doped graphene hydrogels (NGHs) were synthesized through a one-pot hydrothermal route with graphene oxide (GO) as raw material and urea as reducing-doping agents. The morphology, structure, and components of the NGHs were characterized by scanning electron microscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, methylene blue adsorption, thermogravimetric analysis and electrical conductivity measurements. The results demonstrated that nitrogen was doped into the graphene plane at the same time as the GO sheets were reduced, and the nitrogen content incorporated into the graphene lattice was in the range of 3.95 to 6.61 at.% with pyrrolic N as the main component. The NGHs contained about 97.6 wt% water and have a large specific surface area (SSA) of >1300 m² g⁻¹ in the wet state. In addition, the electrochemical performance of the NGHs was investigated. The sample NGHs-4 with a nitrogen content of 5.86 at.% and SSA of 1521 ± 60 m² g⁻¹ in the wet state showed excellent capacitive behavior (308 F g⁻¹ at 3 A g⁻¹) and superior cycling stability (92% retention after 1200 cycles) in 6 mol L⁻¹ KOH. The experimental results indicated that not only the N-content but also the N-type have very significant impact on the capacitive behavior. Furthermore, NGHs strongly influenced the electrochemical properties because of their high SSAs and mesoporous structure.