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- 주제어 : Metal and nitrogen doped graphene (검색결과 3 건)
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Nishan Thilawala, Kondasinghe Gayantha,Kim, Jae-Kwan,Lee, Ji-Myon Elsevier 2019 Journal of Alloys and Compounds Vol.773 No.-
<P><B>Abstract</B></P> <P>Graphene-silver nanowire (AgNW) hybrid structure is a potential candidate to replace indium tin oxide (ITO) owing to its high conductivity, transparency, and flexibility. The thin insulating polyvinylpyrrolidone (PVP) residual surfactant coating that forms on AgNW weakens the wire-to-wire and wire-to-graphene contact, resulting in a higher sheet resistance. For this reason, a post-processing treatment such as high-temperature annealing is usually carried out to reduce the sheet resistance. In this paper, low power nitrogen plasma is utilized to increase the electrical conductivity of the hybrid through the partial removal of PVP and simultaneous doping of graphene without employing any high-temperature annealing treatment. A reduction of over 34% in sheet resistance is obtained for the hybrid compared with a 17% reduction for the AgNW electrode alone. The hybrid electrode, in comparison to the AgNW electrode alone, results in an electrical to optical conductivity ratio (σ<SUB>DC</SUB>/σ<SUB>OP</SUB>) of 234 in 45 s without losing its transparency. In comparison to the 4% reduction of sheet resistance caused by high temperature annealing at 180 °C for 30 min, nitrogen plasma treatment results in a substantially higher reduction (>34%) of the sheet resistance of hybrids in a substantially shorter processing time (45 s).</P> <P><B>Highlights</B></P> <P> <UL> <LI> 30 s grown graphene promoted nitrogen doping up to 9% due to boundary like defects. </LI> <LI> Degradation of PVP improved both the conductivity and transparency of hybrid. </LI> <LI> The hybrid achieved an FOM of 234 compared to the minimum industrial standard of 35 for TCE. </LI> <LI> Sheet resistance reduction of hybrids by N<SUB>2</SUB> plasma was more effective than the use of a high temperature treatment. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Zheng, Yongping,Yang, Dae-Soo,Kweun, Joshua M.,Li, Chenzhe,Tan, Kui,Kong, Fantai,Liang, Chaoping,Chabal, Yves J.,Kim, Yoon Young,Cho, Maenghyo,Yu, Jong-Sung,Cho, Kyeongjae Elsevier 2016 Nano energy Vol.30 No.-
<P><B>Abstract</B></P> <P>Bio-inspired non-precious-metal catalysts based on iron and cobalt porphyrins are promising alternatives to replace costly platinum-based catalysts for oxygen reduction reaction (ORR) in fuel cells. However, the exact nature of the active sites is still not clearly understood, and further optimization design is needed for practical applications. Here, we report a rational catalyst design process by combining density functional theory (DFT) calculations and experimental validations. Two sets of square-planar (MN<SUB>x</SUB>C<SUB>4−x</SUB>) and square-pyramid (MN<SUB>x</SUB>C<SUB>5−x</SUB>) active centers (M=Mn, Fe, Co, Ni) incorporated in graphene were examined using DFT. Fe-N<SUB>5</SUB> and Co-N<SUB>4</SUB> sites were identified theoretically to have the best performance in fuel cells, while Ni-N<SUB>x</SUB>C<SUB>4−x</SUB> sites catalyze the most H<SUB>2</SUB>O<SUB>2</SUB> byproduct. Graphene samples with well-dispersed incorporations of metals were synthesized, and the following electrochemical measurements show an excellent agreement with the theoretical predictions, indicating that a successful design framework and systematic understanding toward the catalytic nature of these materials are established.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Graphene based catalysts design for ORR is demonstrated by combining experiments and modellings. </LI> <LI> Iron porphyrin like active site is unraveled to be five nitrogen coordinated as FeN<SUB>5</SUB>. </LI> <LI> Cobalt porphyrin like active site is shown to be four nitrogen coordinated as CoN<SUB>4</SUB>. </LI> <LI> Nickel porphyrin like catalyst is potentially used for catalytic synthesis of H<SUB>2</SUB>O<SUB>2</SUB>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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