3D porous oxygen-enriched graphene hydrogels with well-balanced volumetric and gravimetric performance for symmetric supercapacitors

3D porous oxygen-enriched graphene hydrogels (POGHs) have been successfully prepared via a one-step hydrothermal approach with graphene oxide and a tiny amount of acidic glutamic acid which serves as carboxyl source, reductant, nitrogen dopant, as well as pore size and density regulator at the same time. Owing to the high content of oxygen-containing functional groups and high density, the repaired graphene sheet structure by nitrogen doping, 3D interconnected porous networks and large specific surface areas, the as-obtained POGHs binder-free electrodes exhibit excellent electrochemical properties in 6 M KOH electrolyte. In particular, the POGH-30-based symmetric supercapacitor displays well-balanced volumetric capacitance (241.1 F cm−3) and gravimetric capacitance (256.5 F g−1) at 0.5 A g−1, and this capacitance can be maintained for 91.8% even at 10 A g−1. Moreover, the POGH-30 electrode also delivers high gravimetric and volumetric specific energy densities of 8.8 Wh kg−1 and 8.3 Wh L−1 at 0.5 A g−1, and excellent cycling stability of 100.7% retention after 10000 cycles at 10 A g−1. These results denote that POGH-30 is expected to be used as electrode material for high-performance supercapacitors.