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

Abstract

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 sp2-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 N2 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 ≈ 88%) after 4000 cycles.

Graphene oxide: strategies for synthesis, reduction and frontier applications

“…Xing et al 212 reported a facile photochemical reduction method for producing the photoreduced graphene hydrogels with 3D porous structures from GO suspension. The supercapacitor based on this structure performed a high specific capacitance of 254 F g -1 at 1 A g -1 in KOH electrolyte.…”

Three dimensional reduced graphene hydrogels with tunable pore sizes using thiourea dioxide for electrode materials in supercapacitors

“…3b, strong vibrations of D bands (the A 1g symmetry mode) in the vicinity of 1349 cm À1 and G bands (the E 2g mode of the sp 2 carbon atoms) in the vicinity of 1596 cm À1 are obviously observed in GO and RGHs. The intensity ratio of I D /I G is 0.89 in GO [41] and increases to 0.99, 1.04 and 1.07 for RGHs-1, RGHs-2 and RGHs-5, which mean the removal of oxygenated groups and reduction of GO. FT-IR spectra is employed to further prove the removal of oxygenated groups by thiourea dioxide with ammonia.…”

“…Besides, the appearance of the new characteristic peak corresponding to C-N bond .7 and 533.6 eV, respectively. All the highresolution XPS spectra demonstrate the effective removal of oxygen-containing groups and doping of nitrogen by thiourea dioxide with ammonia in the reduction process compared to GO [38,41].…”

“…GO which possessed good dispersion in monolayered sheets was synthesized from natural graphite by using modified Hummer's method according to our previous work [38,41]. The concentration of GO suspension was determined by drying small amount of suspension in a vacuum oven at 50 C for 24 h and then weighing the dried GO.…”

Three dimensional nitrogen-doped graphene aerogels functionalized with melamine for multifunctional applications in supercapacitors and adsorption

“…S1) was synthesized from natural graphite by using modified Hummer's method according to our previous work [55,56]. The concentration of GO suspension was determined by drying small amount of suspension in a vacuum oven at 50 °C for 24 h and then weighing the dried GO.…”