Chunnian Chen

Fabrication of functionalized nitrogen-doped graphene for supercapacitor electrodes

A unique and convenient one-step hydrothermal process for synthesizing functionalized nitrogen-doped graphene (FGN) via ethylenediamine, hydroquinone, and graphene oxide (GO) is described. The graphene sheets of FGN provide a large surface area for hydroquinone molecules to be anchored on, which can greatly enhance the contribution of pseudocapacitance. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and electrochemical workstation are used to characterize the materials. The nitrogen content exhibited in FGN can be up to 9.83xa0at.%, and the as-produced graphene material shows an impressive specific capacitance of 364.6xa0Fxa0g−1 at a scan rate of 10xa0mVxa0s−1, almost triple that of the graphene (GN)-based one (127.5xa0Fxa0g−1). Furthermore, the FGN electrodes show excellent electrochemical cycle stability with 94.4xa0% of its initial capacitance retained after 500 charge/discharge cycles at the current density of 3xa0Axa0g−1.

Hollow polypyrrole nanosphere embedded in nitrogen-doped graphene layers to obtain a three-dimensional nanostructure as electrode material for electrochemical supercapacitor

A novel approach was developed to prepare hollow polypyrrole (PPy) nanospheres and nitrogen-doped graphene/hollow PPy nanospheres (NG/H-PPy) composites. In this process, uniform poly (methyl methacrylate-butyl methacrylate-methacrylic acid) (PMMA-PBMA-PMAA) latex microspheres as sacrificial templates were synthesized byxa0using an emulsion polymerization method. Then, hollow PPy nanospheres were obtained on the surface of PMMA-PBMA-PMAA microspheres by in situ chemical oxidative polymerization. Finally, H-PPy was embedded in NG layers successfully through a simple approach. The nanobeads have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectra, and Fourier transform infrared spectra (FTIR). Different electrochemical methods including cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS) have been applied to study the electrochemical properties. The specific capacitance of NG/H-PPy composites based on the three-electrode system is as high as 575xa0F g−1 at a current density of 1xa0A g−1 and enhanced stability about 90.1xa0% after 500xa0cycles, indicating that the composite has an impressive capacitance and excellent cycling performance.

One-step hydrothermal synthesis of nitrogen and sulfur co-doped graphene for supercapacitors with high electrochemical capacitance performance

A facile and effective self-sponsored doping method was introduced via a simple and convenient one-step hydrothermal process. The loose layered and silk-like structure of as-prepared material facilitates hydronium ion diffusion into the outer and inner areas of graphene sheets, which contributes to electric double-layer capacitance, and the anchored functional groups containing N and S greatly enhance pseudocapacitance. The field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction, and electrochemical workstation are used to characterize the materials. The as-produced material shows superior specific capacitance of 302.2xa0Fxa0g−1 at a scan rate of 5xa0mVxa0s−1 and excellent electrochemical stability with 94xa0% of its initial capacitance retained after 1000xa0charge/discharge cycles at the current density of 10xa0Axa0g−1.

Facile fabrication of hollow polyaniline spheres and its application in supercapacitor

Polyaniline (PANI) is a promising electroactive material for pseudocapacitor due to the existence of the electronic conjugation structure. Here we demonstrate a novel approach to prepare hollow polyaniline nanospheres. In this process, uniform poly (methyl methacrylate- butyl methacrylate - methacrylic acid) (PMMA-PBMA-PMAA) latex microspheres as self-sacrificial templates were rapidly prepared through an emulsion polymerization method. Then the hollow PANI (H-PANI) nanospheres were obtained directly through an in-situ chemical oxidative polymerization of aniline in the presence of PMMA-PBMA-PMAA microspheres, which can be explained by the “dissolution” of templates and phase separation between the constituent polymers. The structure and morphology of the nanophase materials have been characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectra. The specific capacitance of H-PANI is 485.5xa0Fxa0g−1 at 1 A g−1 and there is 69% performance attenuation after 500xa0cycles, which show a promising electrochemical performance.