Facile synthesis of hierarchical porous two-dimensional N-doped carbon nanosheets as bi-functional electrode for superior supercapacitor and photo-catalyst

The hierarchical porous nitrogen-doped two-dimensional carbon (HNGC) was prepared by simple calcination of magnesium sulfate (MgSO4) and self-synthesized nitrogen-doped two-dimensional graphene-like carbon at a mild temperature in oxygen. The influence MgSO4 on the morphology, structure and chemical composition of the prepared HNGC samples were studied using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, surface area analysis, X-ray photoelectron microscopy and elemental analyzer. HNGC-2 exhibited a uniform three-dimensional coral-like porous inter-connected structure, large specific surface area, high pore volume, and no loss of nitrogen content. HNGC-2 demonstrated an excellent rate capability of 62.8% at 20 A g−1, outstanding stability of 96.1% following 5000 cycles and the assembled symmetric supercapcitor achieved 12.5 Wh kg−1 at a 350 Wkg-1 and 7.5 Wh kg−1 at 3500 Wkg-1. The novel method was also found to be effective for facilitating the electrochemical performance of commercial biomass active carbon. In addition, HNGC-2 was used for the photo-catalytic degradation of methylene blue and over 99% of methylene blue was successfully degraded under 25-min visible irradiation in the presence of potassium persulfate. The enhanced electrochemical performance and the excellent photo-catalytic performance of HNGC-2 indicated that porous carbon can be successfully activated using an appropriate oxidation strategy.