Ningshuang Zhang

Co9S8 nanoparticles embedded in a N, S co-doped graphene-unzipped carbon nanotube composite as a high performance electrocatalyst for the hydrogen evolution reaction

In this work, we successfully fabricated a three-dimensional (3D) hierarchical ternary composite by embedding Co9S8 nanoparticles in a nitrogen and sulfur co-doped graphene-unzipped carbon nanotube matrix (Co9S8/NSG-UCNTs) through a facile and controllable one-step pyrolysis method using a graphite oxide/oxidized unzipped carbon nanotubes/cobalt nitrate/thiourea composite as the precursor. The as-prepared 3D ternary composite displays superior catalytic performance for the hydrogen evolution reaction (HER), which outperforms most binary or ternary carbon-based composites in the literature. The HER overpotentials are 65 mV and 86 mV when the current densities reach 10 mA cm−2 and 20 mA cm−2, respectively, and the exchange current density reaches 0.503 mA cm−2. Also, it demonstrates good stability reflected from the negligible activity decrease after 1000 consecutive cycles. The excellent electrocatalytic performance of the Co9S8/NSG-UCNT ternary composite is attributed to the co-effect of the abundant HER active sites induced by Co9S8 nanoparticles, structural defects existing in the carbon support caused by N and S co-doping and outstanding conductivity resulting from the 3D structure.

Synthesis of curly graphene nanoribbon/polyaniline/MnO2 composite and its application in supercapacitor

Curly graphene nanoribbon/polyaniline/MnO2 (CGNR/PANI/MnO2) nanocomposites with a unique structure is prepared. The formation mechanism of the CGNR/PANI/MnO2 nanocomposite was proposed, and the morphology and structure were characterized by electron microscopy, X-ray diffraction, and Raman spectroscopy. The CGNR/PANI/MnO2 nanocomposite was investigated for supercapacitor applications. The CGNR/PANI/MnO2 electrode delivered a very high specific capacitance of 496 F g−1, which was much higher than that of CGNR (131 F g−1), PANI (301 F g−1) and MnO2 (33 F g−1), whereas 81.1% of its initial capacitance was retained after 5000 cycles at a scan rate of 50 mV s−1. The CGNR/PANI/MnO2 electrode was also evaluated via a two-electrode configuration, and the supercapacitor delivered a specific capacitance of 103 F g−1. The enhanced electrochemical performance of the CGNR/PANI/MnO2 electrode was ascribed to the unique structure and the synergetic effect of the three components in the composite.

In situ preparation of graphene oxide supported Pd nanoparticles in an ionic liquid and the long-term catalytic stability for the Heck reaction

Palladium (Pd) nanoparticles supported on reduced graphene oxide (Pd/RGO) were successfully prepared in situ in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) ionic liquid (Pd/RGO–IL) by the phase transfer method from water. The prepared Pd/RGO catalyst was characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis. The in situ synthesised Pd nanoparticles were uniformly dispersed on the surface of RGO with an average size distribution of 2 nm. The as-prepared Pd/RGO–IL exhibits good catalytic activity and long-term catalytic stability for Heck reactions in the IL. Initially the product conversion is 95% and still remains at 91% after being cycled ten times. The TEM images of Pd/RGO after the tenth run show that Pd nanoparticles are stably suspended in the IL with an average size of about 2.0 nm and there is almost no agglomeration during the long-term reaction. This may be due to the double protection of the organic cation [BMIM]+ of the IL and the evenly dispersed RGO in the IL. Hence, Pd nanoparticles supported on reduced graphene oxide show remarkable long-term catalytic stability in the IL.