Preparation and electrochemical properties of heteroatom-doped graphene hydrogels

Graphene hydrogel electrode materials doped with nitrogen, phosphorus and sulfur were prepared by a hydrothermal method. SEM, TEM, Raman spectroscopy, XRD and XPS were used to characterize their microstructures and electrochemical properties for use as supercapacitor electrodes. The results indicate that nitrogen, phosphorus and sulfur are doped in the graphene lattice and that they improve the electrochemical performance of graphene with phosphorus being the best of them. Because of their having the largest atomic radius, P atoms produce the largest graphene lattice distortion and significantly increase the specific surface area, which is favorable for fast ion transfer. The capacitance of the P-doped graphene is 388 F/g at a current density of 1 mA/cm² in a 1 mol/L H₂SO₄ electrolyte. A symmetrical cell using the P-doped graphene as the electrodes delivers an energy density of 25.2 Wh/kg at a current density of 1 A/g. The high capacitance of the doped graphene is mainly due to the Faraday pseudocapacitance provided by the heteroatoms.