The Experts below are selected from a list of 1554159 Experts worldwide ranked by ideXlab platform
J P Dodelet - One of the best experts on this subject based on the ideXlab platform.
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fe based catalysts for oxygen reduction in proton exchange membrane fuel cells with cyanamide as nitrogen precursor and or pore filler
2011Co-Authors: Juan Tian, L Birry, Frederic Jaouen, J P DodeletAbstract:Abstract Fe/N/C catalysts for oxygen reduction reaction were synthesized via impregnation or ballmilling. The role of cyanamide (CM) as nitrogen precursor and/or pore-filler for a highly microporous carbon (Black Pearls 2000) was investigated. The use of CM in this work resulted in two main differences compared with phenanthroline from our previous work; (i) ballmilling the precursors did not result in improved activity of the resulting catalysts, and (ii) the activity after the first pyrolysis in argon was relatively high, but did not increase after a second pyrolysis in NH3. These differences may be explained by TGA measurements of both pore-fillers, where complete gasification of CM is observed at temperatures above 750 °C in Ar, while pyrolysis of phenanthroline in Ar results in 20 wt% residual Carbon-Based Material. Consequently, when using CM as pore-filler with a highly microporous carbon support, the maximum microporous surface area and nitrogen content is reached after only a single pyrolysis in Ar. The most active catalyst prepared with CM was obtained by pyrolysing in Ar at 950 °C a catalyst precursor containing 1 wt% Fe, 80 wt% CM and Black Pearls 2000. This catalyst possessed about 1/6th the catalytic activity of best reported using phenanthroline as a pore-filler. Changing the carbon support had effects on the activity and stability of the catalysts. The catalysts made with a non-porous furnace black (N330) or carbon nanotubes as a carbon support were more stable but less performing than those using carbon supports having high microporous surface area like Black Pearls 2000 or Ketjenblack. The desirable properties for a pore-filler molecule used in the synthesis of Fe/N/C-catalysts by the pore-filling method are discussed.
Hoeil Chung - One of the best experts on this subject based on the ideXlab platform.
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reduced graphene oxide nickel sulfide nis composited on mechanical pencil lead as a versatile and cost effective sensor for electrochemical measurements of bisphenol a and mercury ii
2019Co-Authors: Tung Duy Vu, Hoeil ChungAbstract:Abstract NiS is a highly promising transition metal sulfide versatile for a sensor Material owing to its superior conductivity and stability, and herein we report its first incorporation into an electrochemical sensor. Because exposure to electrolyte under electrochemical impact can easily deform NiS, thereby decreasing its electro-activity and measurement reproducibility, a strategy for optimally integrating NiS into sensors is critically necessary. For this purpose, NiS was initially firmly affixed to a mechanical pencil lead (MPL) by means of hydrothermal deposition (with the result designated as MPL-NiS). MPL, a commercially available Carbon-Based Material with consistent quality, was adopted to make the sensor cost-effective and easily prepared. Then, to prevent direct exposure of NiS to samples during electrochemical measurement and to make the sensor surface more reactive for wide variety of analytes, reduced graphene oxide (rGO) was electrodeposited on the NiS surface to construct a final structure of MPL-NiS/rGO. In summary, NiS, a p-type semiconductor with positive charge, was effectively composited and sandwiched with negatively charged rGO and MPL by means of mutual electrostatic interaction. When the developed MPL-NiS/rGO sensor was used to separately measure bisphenol A (BPA) and mercury- Hg2+, the sensitivity and sensor-to-sensor reproducibility were comparable with or superior to those of previously reported sensors.
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a mechanical pencil lead supported carbon nanotube au nanodendrite structure as an electrochemical sensor for as iii detection
2016Co-Authors: Jong Ryeul Sohn, Hoeil ChungAbstract:A mechanical pencil lead (MPL), an easily obtainable Carbon-Based Material with a consistent size, was used as a frame to construct an MPL-supported carbon nanotube/Au nanodendrite (MPL-CNT/AuND) sensor through simple electrodeposition of Au onto the MPL in the presence of CNTs. A nanodendrite structure was adopted to ensure large numbers of active electrochemical sites because of its hierarchical structure with well-aligned terraces; the CNTs were used to firmly adhere the fabricated Au nanodendrites to the MPL surface to ensure ruggedness. The MPL-CNT/AuND structure was used to measure As3+ samples in a concentration range from 0.5 to 80 ppb using anodic stripping voltammetry (ASV). The variation in peak intensities was linear (R2: 0.997), and the limit of detection (LOD) was 0.4 ppb. The average relative standard deviation (RSD) of the peak intensities from the voltammograms of each sample collected using three separately prepared MPL-CNT/AuNDs was 8.7%, thereby demonstrating good sensor-to-sensor reproducibility. Furthermore, when three As3+ samples prepared in tap water were measured, the accuracy was maintained without noticeable degradation and the response was steady up to 50-cycle measurements.
Juan Tian - One of the best experts on this subject based on the ideXlab platform.
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fe based catalysts for oxygen reduction in proton exchange membrane fuel cells with cyanamide as nitrogen precursor and or pore filler
2011Co-Authors: Juan Tian, L Birry, Frederic Jaouen, J P DodeletAbstract:Abstract Fe/N/C catalysts for oxygen reduction reaction were synthesized via impregnation or ballmilling. The role of cyanamide (CM) as nitrogen precursor and/or pore-filler for a highly microporous carbon (Black Pearls 2000) was investigated. The use of CM in this work resulted in two main differences compared with phenanthroline from our previous work; (i) ballmilling the precursors did not result in improved activity of the resulting catalysts, and (ii) the activity after the first pyrolysis in argon was relatively high, but did not increase after a second pyrolysis in NH3. These differences may be explained by TGA measurements of both pore-fillers, where complete gasification of CM is observed at temperatures above 750 °C in Ar, while pyrolysis of phenanthroline in Ar results in 20 wt% residual Carbon-Based Material. Consequently, when using CM as pore-filler with a highly microporous carbon support, the maximum microporous surface area and nitrogen content is reached after only a single pyrolysis in Ar. The most active catalyst prepared with CM was obtained by pyrolysing in Ar at 950 °C a catalyst precursor containing 1 wt% Fe, 80 wt% CM and Black Pearls 2000. This catalyst possessed about 1/6th the catalytic activity of best reported using phenanthroline as a pore-filler. Changing the carbon support had effects on the activity and stability of the catalysts. The catalysts made with a non-porous furnace black (N330) or carbon nanotubes as a carbon support were more stable but less performing than those using carbon supports having high microporous surface area like Black Pearls 2000 or Ketjenblack. The desirable properties for a pore-filler molecule used in the synthesis of Fe/N/C-catalysts by the pore-filling method are discussed.
K Ziegler - One of the best experts on this subject based on the ideXlab platform.
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nonlinear electromagnetic response of graphene frequency multiplication and the self consistent field effects
2008Co-Authors: S A Mikhailov, K ZieglerAbstract:Graphene is a recently discovered Carbon-Based Material with unique physical properties. This is a monolayer of graphite, and the two-dimensional electrons and holes in it are described by the effective Dirac equation with a vanishing effective mass. As a consequence, the electromagnetic response of graphene is predicted to be strongly nonlinear. We develop a quasi-classical kinetic theory of the nonlinear electromagnetic response of graphene, taking into account the self-consistent-field effects. The response of the system to both harmonic and pulse excitation is considered. The frequency multiplication effect, resulting from the nonlinearity of the electromagnetic response, is studied under realistic experimental conditions. The frequency upconversion efficiency is analyzed as a function of the applied electric field and parameters of the samples. Possible applications of graphene in terahertz electronics are discussed.
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nonlinear electromagnetic response of graphene frequency multiplication and the self consistent field effects
2008Co-Authors: S A Mikhailov, K ZieglerAbstract:Graphene is a recently discovered carbon based Material with unique physical properties. This is a monolayer of graphite, and the two-dimensional electrons and holes in it are described by the effective Dirac equation with a vanishing effective mass. As a consequence, electromagnetic response of graphene is predicted to be strongly non-linear. We develop a quasi-classical kinetic theory of the non-linear electromagnetic response of graphene, taking into account the self-consistent-field effects. Response of the system to both harmonic and pulse excitation is considered. The frequency multiplication effect, resulting from the non-linearity of the electromagnetic response, is studied under realistic experimental conditions. The frequency up-conversion efficiency is analysed as a function of the applied electric field and parameters of the samples. Possible applications of graphene in terahertz electronics are discussed.
Junyan Zhang - One of the best experts on this subject based on the ideXlab platform.
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direct synthesis of nitrogen doped carbon nanosheets with high surface area and excellent oxygen reduction performance
2014Co-Authors: Qiao Liu, Youxin Duan, Qiuping Zhao, Fuping Pan, Bin Zhang, Junyan ZhangAbstract:Graphene-like nitrogen-doped carbon nanosheets (NCN) have become a fascinating Carbon-Based Material for advanced energy storage and conversion devices, but its easy, cheap, and environmentally friendly synthesis is still a grand challenge. Herein we directly synthesized porous NCN Material via the facile pyrolysis of chitosan and urea without the requirement of any catalyst or post-treatment. As-prepared Material exhibits a very large BET surface area of ∼1510 m2 g–1 and a high ratio of graphitic/pyridinic nitrogen structure (2.69 at. % graphitic N and 1.20 at. % pyridinic N). Moreover, compared to a commercial Pt/C catalyst, NCN displays excellent electrocatalytic activity, better long-term stability, and methanol tolerance ability toward the oxygen reduction reaction, indicating a promising metal-free alternative to Pt-based cathode catalysts in alkaline fuel cells. This scalable fabrication method supplies a low-cost, high-efficiency metal-free oxygen reduction electrocatalyst and also suggests an eco...