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【lecture】Graphene-Tubes for Oxygen Reduction Electrocatalysis
Published:2015-06-20 Hits:520

Speaker: Gang Wu

Assistant Professor, University at Buffalo, the State University of New York, Buffalo, New York 14260, United States

Time: July 7th (Tuesday), 13:30

Venue: Room 226, Department of Environmental Science and Engineering

Abstract

        A new method to prepare N-doped carbon nanotubes with large diameters (up to 500 nm) and relatively thin walls (less than 10 layers) was discovered, which we call N-doped graphene tubes (N-GTs). Although the large-diameter tubes contain multiple graphene layers, their wall thickness and ratio of wall thickness to tube diameter are small compared to conventional multi-walled carbon nanotubes (MWNTs). As a result, their surface areas are higher than conventional MWNTs. We also demonstrate an effective strategy for tuning the size of large-diameter nitrogen-doped graphene tubes (N-GT) from 50 to 200 nm by varying the transition metal (M=Fe, Co, Ni or Mn) used to catalyze the graphitization of dicyanamide. Fe yielded the largest tube size, followed by Co and Ni. Rather than generating tubes, Mn produced a clot-like carbon morphology. We correlate the carbon morphology to electrochemical properties to guide the development of high-performance precious metal-free catalysts for the oxygen reduction reaction (ORR). The Fe-derived N-GTs, which had the largest diameter, exhibited the highest activity for the ORR in alkaline media as well as in a more challenging acidic electrolyte. A clear trend of Fe > Co > Ni > Mn for the ORR catalytic activity was observed. The Fe-derived carbon material also exhibited the highest BET surface area (~870 m2/g) and electrochemically accessible surface area (~450 m2/g). The Fe-derived G-NTs had the highest concentration of nitrogen incorporated into the graphene planes. Thus, in addition to the intrinsic high activity of Fe catalysts, the high surface area and nitrogen doping contribute to high ORR activity. 

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