The replacement of precious metal catalysts with pyridinic and graphitic-N sites that are earth-abundant and of low-cost and enriched with a high concentration for oxygen reduction reaction (ORR) is highly desirable. Herein, we report a facile synthesis of N-doped hollow mesoporous carbon spheres (NHSs) using tetraethyl orthosilicate (TEOS) as a silica precursor and dopamine hydrochloride (DHC) as carbon and nitrogen precursors through which uniform hollow sphere mesopores can be attained by adjusting the temperature and DHC loading. At the optimum temperature of 900 °C, a concentration ratio (0.5 mL:0.4 g) of TEOS/DHC leads to high-surface-area (1452 m 2 /g) carbon with pore volume (0.3 cm 3 /g), enriched defect sites, and a large number of pyridinic and graphitic-N sites offering an outstanding activity toward ORR. Further electrochemical studies demonstrated a positive onset potential of 0.84 V, an excellent current density of 4.9 mA/cm 2 , and a four-electron pathway with a lower Tafel slope of 65 mV/dec, respectively.
Available online xxxKeywords: Hydrothermal method MoS 2 Nano shapes HER PEM electrolyser Hydrogen production a b s t r a c t In this work, we developed a simple and cost-effective hydrothermal route to regulate the formation of molybdenum disulfide (MoS 2 ) in different morphologies, like, nano-sheet, nano-capsule and nano-flake structure by controlling the reaction temperature and sulphur precursor employed. Such a fine tuning of different morphologies yields a leverage to obtain novel shapes with high surface area to employ them as suitable candidates for hydrogen evolution catalysts. Moreover, we report here the first time observation of MoS 2 nano-capsule formation via environmentally benign hydrothermal route and characterized them by X-ray diffraction (XRD), nitrogen adsorption and desorption by Brunaer eEmmetteTeller (BET) method, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray photo-electron spectroscopy (XPS) techniques. MoS 2 nanocapsules exhibits superior activity towards hydrogen evolution reaction (HER) with a low over-potential of 120 mV (RHE), accompanied by large exchange current density and excellent stability in 0.5 M H 2 SO 4 solution. MoS 2 nano-capsule catalyst was coated on solid proton conducting membrane (Nafion) and IrO 2 as anode catalyst. The performance of the catalyst was evaluated in MEA mode for 200 h at 2 V without any degradation of electrocatalytic activity.ScienceDirect j o urn al h om epa ge: www.elsev ier.com/locate/he i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e1 0 http://dx.
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