UV-Assisted Photoreduction of Graphene Oxide into Hydrogels: High-Rate Capacitive Performance in Supercapacitor

Self-assembly of graphene oxide (GO) into three-dimensional (3D) macroscopic architectures is an efficient strategy to exploit their inherent properties fully and restrict the formation of irreversible aggregates or restack into graphitic structure. In the present work, we first report a photoreduction method for producing the 3D photoreduced graphene hydrogels (PRGHs) through self-assembly of GO suspension under photochemical reduction of Hantzsch 1,4-dihydropyridine (HEH). The reduction of GO into PRGHs was confirmed by X-ray powder diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), elemental analysis, and Fourier transform infrared spectroscopy (FT-IR). It is observed that most of the oxygenated groups could be efficiently removed, and the sp(2)-like domains are restored as a result of photoreduction process. The 3D hierarchically porous structures of the resulting PRGHs have been intensively investigated by field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and N-2 sorption measurement. More interestingly, the supercapacitor based on the PRGHs showed a high specific capacitance of 254 F g(1) at 1 A g(1) in KOH electrolyte. The specific capacitance can still be maintained for 64% with an increase of the discharging current density to 4 A g(1). It also showed that the electrode based on PRGHs has good stability and high reversibility in the charge/discharge cycling test. The specific capacitance of the supercapacitor maintained at 224 F g(1) (capacitance retention approximate to 88%) after 4000 cycles.