N/O co-enriched graphene hydrogels as high-performance electrodes for aqueous symmetric supercapacitors

In this study, an easy one-pot hydrothermal strategy was used to prepare N/O co-enriched graphene hydrogels (NOGHs) using graphene oxide (GO) solution and n-propylamine as a reactant. The n-propylamine can be used not only as a reductant, nitrogen dopant and structure regulator, but also as a spacer to inhibit the agglomeration of graphene sheets. Benefiting from the synergistic effect between the heteroatoms (N, O), 3D porous structures and high specific surface area, the as-prepared NOGH samples present excellent electrochemical properties. Remarkably, the NOGH-140 based binder-free symmetric supercapacitor shows a high specific capacitance of 268.1 F g^-1 at the current density of 0.3 A g^-1 and retains 222.5 F g^-1 (82.9% of its initial value) at 10.0 A g^-1 in 6 M KOH electrolyte. Furthermore, the assembled device also displays a notable energy density (9.3 W h kg^-1) and outstanding cycling performance (1.8% increase of its initial specific capacitance after 10 000 cycles at 10 A g^-1). The simple preparation method and excellent electrochemical properties indicate that NOGHs can be used as electrode materials for commercial supercapacitors.