Systematic study on structural and electronic properties of diamine/triamine functionalized graphene networks for supercapacitor application

In this report, a series of diamine/traimine molecules were selected to make different functionalized graphene networks using a facile two-step hydrothermal method. The molecular level grafting of amines to graphene surface via covalent bonds was confirmed by FTIR and XPS. XRD patterns revealed that these amine molecules served as molecular spacers to enlarge the interlayer spacing and the specific surface area. Upon functionalization, the interlayer spacing values varied from 0.84 to 1.23 nm, and the spacing was found to change negligibly after the GO reduction, implying the high stability of the 3D graphene nanostructure. The influence of chain conformation and degree of functionalization on molecular spacing was also discussed. The as-fabricated graphene composite exhibited an improved capacitance in aqueous and organic electrolytes with less than 10% capacitance decay during 10,000 charge/discharge cycles and fast ionic diffusion features. The composite also delivered a maximum capacitance of 119 F/g in ionic liquid electrolyte with an ultrahigh energy density of 51 Wh/kg and slow self-discharge rate. Furthermore, computational study was performed to model the electron distribution and band gap structures of graphene networks. The use of aliphatic amine spacers could better elucidate the correlation between spacing effect and electrical double-layer capacitance.