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Nitrogen-containing activated carbons were prepared from chitosan, a widely available and inexpensive biopolysaccharide, by a simple procedure and tested as electrode material in supercapacitors. The physical activation of chitosan chars with CO 2 led to carbons with a very high nitrogen content (up to 5.4 wt%) and moderate surface areas (1000-1100 m 2 g -1 ). Only chitosan-based activated carbons with a similar microporous structure were considered in this study to evaluate the effect of the nitrogen content and distribution on their electrochemical performance. The N-containing activated carbons were tested in two-and three-electrode supercapacitors using an aqueous electrolyte (1 M H 2 SO 4 ), and they exhibited superior surface capacitance (19.5 lF cm -2 ) and pseudocapacitance compared to a commercial activated carbon with a negligible nitrogen content and similar microporosity. The low oxygen content and the presence of stable quaternary nitrogen improved the charge propagation on the chitosan-based carbons, which was confirmed by the high capacity retention of 83 %. The chitosan-based carbons exhibited excellent cyclic stability and maintained 100 % of their capacitance after 5000 charge/discharge cycles at a current density of 1 A g -1 . These results demonstrate the suitability of chitosan-based carbons for application in energy storage systems.Electronic supplementary material The online version of this article

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In our study, we report a facile solvothermal method for the synthesis of Bi 2 S 3 nanoparticles with unique morphologies using water and mixed solvent systems, such as ethylene glycol/water (1:1, v/v) and butyldiglycol/water (1:1, v/v). Altering the solution mixtures used in the solvothermal synthesis allowed the shape of the Bi 2 S 3 nanoparticles to be controlled. The synthesis of Bi 2 S 3 in water at 150°C for 24 h led to the formation of sphere-like particles 100-300 nm in size. Very uniform spherical nanospheres with diameters from 50 to 90 nm formed when ethylene glycol/water mixture (1:1, v/v) was used as the solvent under the same solvothermal conditions. The butyldiglycol/water mixture promoted the formation of plate-shaped Bi 2 S 3 nanoparticles composed of nanorods. The electrochemical properties of the Bi 2 S 3 samples were determined in a three-electrode cell in 6 mol L -1 KOH using cyclic voltammetry, galvanostatic charging/discharging and impedance spectroscopy. Among the synthesized materials, the Bi 2 S 3 sample obtained in the butyldiglycol/water mixture exhibited a superior capacitive behavior with an outstanding capacitance of 550 F g -1 (at 0.5 A g -1 ), and great cycle stability, which was reflected by a capacitance retention of 87% after 500 charge/discharge cycles. These results demonstrate the high potential of Bi 2 S 3 as an active electrode material for supercapacitors.

Carbon nanofibers (CNFs) were grown using catalytic chemical vapor deposition (CCVD) with methane as the carbon source and a hydroxyapatite-supported nickel catalyst (Ni/HAp). The catalyst, which contained approximately 14 wt% Ni, was prepared using the incipient wetness method with an aqueous nickel nitrate solution. Temperature-programmed reduction and X-ray diffraction were used to characterize the active phase of Ni/HAp. Three variables were evaluated to optimize the CNF growth process, including the temperature and the time of catalyst reduction as well as the reaction time, at 650°C. Regardless of the applied CCVD process conditions, herringbone bamboo-like CNFs were grown during methane decomposition over Ni/HAp, which was confirmed using transmission electron microscopy. A high CNF yield of nearly 10 g CNF g cat -1was achieved at 650°C after a reaction time of 3 h when the catalyst was subjected to a reduction at the same temperature for 2 h under a hydrogen flow prior to synthesis. As the reduction temperature increased from 450 to 650°C, both the yield and diameters of the CNFs increased. The beneficial effects of including hydrogen in the reaction mixture on the catalytic performance of Ni/ HAp and the purity of the grown CNFs were demonstrated.