Exploration of the Active Center Structure of Nitrogen-Doped Graphene for Control over the Growth of Co₃O₄ for a High-Performance Supercapacitor

Nitrogen-doped graphene sheets with different active center structures, such as amine N, quaternary N, pyridinic N, or pyrrolic N atoms, were successfully fabricated using targeted nitrogen precursors and a designed annealing process. Then, the nitrogen-doped graphene with a different structure is used as the active center for the growth of Co3O4 nanoparticles. The investigation results reveal that the interaction between loaded Co3O4 particles and amine N atoms doped in graphene sheets is stronger than those of quaternary N, pyridinic N, or pyrrolic N atoms, and leads to a smaller particle size of Co3O4 and a high specific surface area of composite electrodes which perform with better electrochemical behavior. The Co3O4/N-RGO 550 °C dominated with amine N atoms exhibits the highest capacitance of 3553 and 1967 F g–1 at 1 and 15 A g–1, respectively, which are apparently higher values than those of the other Co3O4 composite grown on the nitrogen-doped graphene dominated with pyridinic N, pyrrolic N, or quaternary N atoms, respectively, and those of previously reported Co3O4 with different morphology or Co3O4 composite materials. Moreover, an electrode prepared from Co3O4/N-RGO 550 °C dominated with amine N atoms also has an excellent cycling stability with >90% capacity retention after 3000 cycles at 5 A g–1. The stronger interaction between Co3O4 and amine N atoms doped in graphene sheets, which facilitate the formation of smaller Co3O4 particle sizes to form higher specific surface and desired pore size distribution to enhance the capacitance and make the Co3O4/N-RGO 550 °C extremely stable for capacitive energy storage, suggest the potential usage of the Co3O4/N-RGO 550 °C composite as high-supercapacitor electrode materials.