The co-doping of graphene with nitrogen and sulfur was investigated aiming at understanding their interactions with the presence of oxygen in graphene. The co-doped graphene (NS-G) was synthesized via a one-pot hydrothermal route using graphene oxide as starting material and L-cysteine, an amino acid containing both N and S, as the doping agent. The obtained NS-G with a three-dimensional hierarchical structure containing both macropores and mesopores exhibited excellent mechanical stabilities under both wet and dry conditions. As compared to N or S singly doped graphene, the co-doped sample contains significantly higher concentrations of N and S species especially pyrollic N groups. The co-doped sample considerably outperformed the singly doped samples when used as free-standing electrode in supercapacitors due to enhanced pseudocapacitance. The simultaneous incorporation of S and N species with the presence of oxygen significantly modified the surface chemistry of carbon leading to considerably higher doping levels, although directly bonding between N and S is neither likely nor detected. Hence, the synergetic effect between N and S occurred through carbon atoms in neighboring hexagonal rings in a graphene sheet.

Porous carbons integrated with high gravimetric/volumetric/areal capacitances, especially at high mass loadings (>10 mg cm−2), are important for practical applications in supercapacitors. Here, a strategy is developed for the synthesis of ultramicroporous carbons puzzled by graphene quantum dots as the building units through chemical welding and in situ activation. The resulted carbon has unique ultramicroporous structure (≈0.5 nm) with both high surface area (1730 m2 g−1) and packing density (0.97 g cm−3), providing high gravimetric and volumetric capacitances of 270 F g−1 and 262 F cm−3 at 1 A g−1, respectively. More importantly, such carbon achieves an ultrahigh areal capacitance of 5.70 F cm−2 with a high mass loading of 25 mg cm−2 at 1 A g−1, which is one of the best among the previously reported porous carbons. Furthermore, a two‐electrode supercapacitor exhibits an ultrahigh areal capacitance of 3 F cm−2 at 0.5 A g−1, rapid charge–discharge ability, and long lifespan. This work paves an avenue for developing advanced porous carbons with integrated capacitive performances for supercapacitors.

Nitrogen-doped graphene hydrogels were synthesized using amino acids as doping agents. The acidity of the amino acid affects the morphology and ultimately the electrochemical performance of the material.

The capacitive energy storage performance of activated carbon can be significantly improved by embedding graphene quantum dots owing to the formation of overall conductive networks.

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Porous carbon nanofibers were prepared by electrospinning using coal as the raw material. The activated carbon fiber mat is a promising candidate for the electrode of supercapacitors.

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