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Formation of active sites for Oxygen reduction reactions by transformation of Nitrogen functionalities in Nitrogen-doped Carbon nanotubes
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
2012 (English)In: ACS Nano, ISSN 1936-0851, Vol. 6, no 10, 8904-8912 p.Article in journal (Refereed) Published
Abstract [en]

Heat treating nitrogen-doped multiwalled carbon nanotubes containing up to six different types of nitrogen functionalities transforms particular nitrogen functionalities into other types which are more catalytically active toward oxygen reduction reactions (ORR). In the first stage, the unstable pyrrolic functionalities transform into pyridinic functionalities followed by an immediate transition into quaternary center and valley nitrogen functionalities. By measuring the electrocatalytic oxidation reduction current for the different samples, we achieve information on the catalytic activity connected to each type of nitrogen functionality. Through this, we conclude that quaternary nitrogen valley sites, N-Q(valley), are the most active sites for ORR in N-CNTs. The number of electrons transferred in the ORR is determined from ring disk electrode and rotating ring disk electrode measurements. Our measurements indicate that the ORR processes proceed by a direct four-electron pathway for the N-Q(valley) and the pyridinic sites while it proceeds by an indirect two-electron pathway via hydrogen peroxide at the N-Q(center) sites. Our study gives both insights on the mechanism of ORR on different nitrogen functionalities in nitrogen-doped carbon nanostructures and it proposes how to treat samples to maximize the catalytic efficiency of such samples.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2012. Vol. 6, no 10, 8904-8912 p.
Keyword [en]
nitrogen-doped carbon nanotubes, nitrogen functionalities, X-ray photoelectron spectroscopy, electrochemistry, cyclic voltammetry, oxygen reduction reactions
National Category
Physical Sciences Chemical Sciences Nano Technology
URN: urn:nbn:se:umu:diva-61776DOI: 10.1021/nn302906rISI: 000310096100049OAI: diva2:572459
Available from: 2012-11-27 Created: 2012-11-26 Last updated: 2015-03-09Bibliographically approved
In thesis
1. Efficient electrocatalysts based on nitrrogen-doped carbon nanostructures for energy applications
Open this publication in new window or tab >>Efficient electrocatalysts based on nitrrogen-doped carbon nanostructures for energy applications
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Carbon nanostructures have emerged as a key material in nanotechnology and continuously find new areas of applications. Particularly, they are attractive due to their excellent properties as support for catalyst nanostructures leading to highly efficient composite materials for various electrochemical applications. The interest in these structures is further increased by the possibility to alter their electronic and structural properties by various methods. Heteroatom doping of carbon nanostructures is one of the approaches which may induce intrinsic catalytic activity in these materials. In addition, such introduction of guest elements into the hexagonal carbon skeleton provides strong nucleation sites which facilitate the stabilization of nanostructures on their surface. In this thesis we present detailed studies on the nitrogen incorporation into carbon nanostructures, particularly carbon nanotubes and reduced graphene oxide. Due to the high impact of nitrogen configuration on the intrinsic electrocatalytic properties of carbon nanostructures, we investigated the nitrogen functionalities using X-ray photoelectron spectroscopy and Raman spectroscopy. Based on our achievements we could assign the most electrocatalytic active nitrogen site in nitrogen-doped carbon nanotubes (NCNTs) for catalytic oxygen reduction reaction (ORR) which is an important reaction in energy conversion systems such as fuel cells. We then used nitrogen-doped carbon nanostructures as a key component to manufacture hybrid material, where the nitrogen doped nanostructures has a role of both stabilizing the nanostructures and to work as conductive additive to assist the charge transfer from the other constituents suffering from inherently poor conductivity. Our hybrid material comprising transition metal oxides (Fe2O3 and Co3O4) anchored on nitrogen-doped carbon nanostructure were used to both manufacture an exotic type of graphene nanoscrolls, as well as studied and evaluated as an electrocatalyst in various electrochemical reactions. We show that the self-assembled electrodes exhibited better performance and higher stability compared to when the same material was loaded on common current collectors such as fluorine tin oxide (FTO) coated glass and glassy carbon electrode, with both higher current densities, more efficient charge transfer and lower overpotentials for oxygen evolution and hydrogen evolution reactions, the two important processes in a water splitting device. Our NCNTs-based electrodes showed further excellent performance in lithium ion batteries with high cyclability and capacity. The thesis gives insight into processes, materials, and methods that can be utilized to manufacture an efficient water splitting device, based on earth-abundant self-assembled materials. It further represents a significant advancement of the role of nitrogen in heteroatom-doped nanostructures, both regarding their intrinsic catalytic activity, as well as their role for stabilizing nanostructures.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2015. 76 p.
National Category
Condensed Matter Physics
Research subject
urn:nbn:se:umu:diva-100676 (URN)978-91-7601-214-7 (ISBN)
Public defence
2015-03-31, Naturvetarhuset, N420, Umeå University, Umeå, 13:00 (English)
Available from: 2015-03-10 Created: 2015-03-06 Last updated: 2015-05-08Bibliographically approved

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Sharifi, TivaHu, GuangzhiJia, XueenWågberg, Thomas
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