umu.sePublications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Efficient electrocatalysts based on nitrrogen-doped carbon nanostructures for energy applications
Umeå University, Faculty of Science and Technology, Department of Physics.
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
Physics
Identifiers
URN: urn:nbn:se:umu:diva-100676ISBN: 978-91-7601-214-7 (print)OAI: oai:DiVA.org:umu-100676DiVA: diva2:793079
Public defence
2015-03-31, Naturvetarhuset, N420, Umeå University, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2015-03-10 Created: 2015-03-06 Last updated: 2017-03-21Bibliographically approved
List of papers
1. Nitrogen doped multi walled carbon nanotubes produced by CVD-correlating XPS and Raman spectroscopy for the study of nitrogen inclusion
Open this publication in new window or tab >>Nitrogen doped multi walled carbon nanotubes produced by CVD-correlating XPS and Raman spectroscopy for the study of nitrogen inclusion
Show others...
2012 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 50, no 10, 3535-3541 p.Article in journal (Refereed) Published
Abstract [en]

High purity aligned nitrogen doped multi walled carbon nanotubes were synthesized by the catalytic chemical vapor deposition method using pyridine and Fe/Co (2:1 volume ratio) as the single C/N precursor and catalyst material. The average diameter of the synthesized tubes ranges between 29 nm and 57 nm and the nitrogen content of the tubes reaches a maximum of 9.2 (at.)% nitrogen. The effect of nitrogen doping on the Raman scattering of doped tubes and its correlation with X-ray photoelectron spectra (XPS) was investigated. The analysis is based on the investigation of the I-D/I-G (integrated area ratio), other nitrogen characteristic Raman modes and the type of nitrogen inclusion interpreted from the N 1s electron bonding energies in XPS. At doping levels higher than 5% the nitrogen inclusion takes place through another mechanism than at low nitrogen doping levels. Most significant is that pyridinic defects are relatively readily incorporated at low nitrogen doping levels while at nitrogen content higher than 5% the major incorporation mechanism is dominated by pyridinic and pyrrolic defects on an equal basis. Our study gives further insight into nitrogen doping effects and the relation between type of nitrogen inclusion and nitrogen doping levels. (C) 2012 Elsevier Ltd. All rights reserved.

National Category
Materials Chemistry
Identifiers
urn:nbn:se:umu:diva-57740 (URN)10.1016/j.carbon.2012.03.022 (DOI)000305851700021 ()
Available from: 2012-08-20 Created: 2012-08-14 Last updated: 2017-12-07Bibliographically approved
2. Formation of active sites for Oxygen reduction reactions by transformation of Nitrogen functionalities in Nitrogen-doped Carbon nanotubes
Open this publication in new window or tab >>Formation of active sites for Oxygen reduction reactions by transformation of Nitrogen functionalities in Nitrogen-doped Carbon nanotubes
2012 (English)In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, 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
Keyword
nitrogen-doped carbon nanotubes, nitrogen functionalities, X-ray photoelectron spectroscopy, electrochemistry, cyclic voltammetry, oxygen reduction reactions
National Category
Physical Sciences Chemical Sciences Nano Technology
Identifiers
urn:nbn:se:umu:diva-61776 (URN)10.1021/nn302906r (DOI)000310096100049 ()
Available from: 2012-11-27 Created: 2012-11-26 Last updated: 2017-12-07Bibliographically approved
3. Formation of nitrogen-doped graphene nanoscrolls by adsorption of magnetic gamma-Fe2O3 nanoparticles
Open this publication in new window or tab >>Formation of nitrogen-doped graphene nanoscrolls by adsorption of magnetic gamma-Fe2O3 nanoparticles
Show others...
2013 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 4, 2319- p.Article in journal (Refereed) Published
Abstract [en]

Graphene nanoscrolls are Archimedean-type spirals formed by rolling single-layer graphene sheets. Their unique structure makes them conceptually interesting and understanding their formation gives important information on the manipulation and characteristics of various carbon nanostructures. Here we report a 100% efficient process to transform nitrogen-doped reduced graphene oxide sheets into homogeneous nanoscrolls by decoration with magnetic gamma-Fe2O3 nanoparticles. Through a large number of control experiments, magnetic characterization of the decorated nanoparticles, and ab initio calculations, we conclude that the rolling is initiated by the strong adsorption of maghemite nanoparticles at nitrogen defects in the graphene lattice and their mutual magnetic interaction. The nanoscroll formation is fully reversible and upon removal of the maghemite nanoparticles, the nanoscrolls return to open sheets. Besides supplying information on the rolling mechanism of graphene nanoscrolls, our results also provide important information on the stabilization of iron oxide nanoparticles.

Place, publisher, year, edition, pages
Nature Publishing Group, 2013
National Category
Physical Sciences Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-80760 (URN)10.1038/ncomms3319 (DOI)000323752300004 ()
Available from: 2013-10-03 Created: 2013-09-25 Last updated: 2017-12-06Bibliographically approved
4. Hierarchical self-assembled structures based on nitrogen-doped carbon nanotubes as advanced negative electrodes for Li-ion batteries and 3D microbatteries
Open this publication in new window or tab >>Hierarchical self-assembled structures based on nitrogen-doped carbon nanotubes as advanced negative electrodes for Li-ion batteries and 3D microbatteries
Show others...
2015 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 279, 581-592 p.Article in journal (Refereed) Published
Abstract [en]

Hierarchical structures based on carbon paper and multi-walled nitrogen-doped carbon nanotubes were fabricated and subsequently decorated with hematite nanorods to obtain advanced 3D architectures for Li-ion battery negative electrodes. The carbon paper provides a versatile metal-free 3D current collector ensuring a good electrical contact of the active materials to its carbon fiber network. Firstly, the nitrogen-doped carbon nanotubes onto the carbon paper were studied and a high footprint area capacity of 2.1 mAh cm−2 at 0.1 mA cm−2 was obtained. The Li can be stored in the inter-wall regions of the nanotubes, mediated by the defects formed on their walls by the nitrogen atoms. Secondly, the incorporation of hematite nanorods raised the footprint area capacity to 2.25 mAh cm−2 at 0.1 mA cm−2. However, the repeated conversion/de-conversion of Fe2O3 limited both coulombic and energy efficiencies for these electrodes, which did not perform as well as those including only the N-doped carbon nanotubes at higher current densities. Thirdly, long-cycling tests showed the robust Li insertion mechanism in these N-doped carbonaceous structures, which yielded an unmatched footprint area capacity enhancement up to 1.95 mAh cm−2 after 60 cycles at 0.3 mA cm−2 and an overall capacity of 204 mAh g−1 referred to the mass of the entire electrode.

National Category
Other Physics Topics
Identifiers
urn:nbn:se:umu:diva-98960 (URN)10.1016/j.jpowsour.2015.01.036 (DOI)000350919600067 ()
Available from: 2015-01-29 Created: 2015-01-29 Last updated: 2017-12-05Bibliographically approved
5. Maghemite nanorods anchored on a 3D nitrogen-doped carbon nanotubes substrate as scalable direct electrode for water oxidation
Open this publication in new window or tab >>Maghemite nanorods anchored on a 3D nitrogen-doped carbon nanotubes substrate as scalable direct electrode for water oxidation
Show others...
2016 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 41, no 1, 69-78 p.Article in journal (Refereed) Published
Abstract [en]

A hybrid catalyst 3D electrode for electrochemical water oxidation to molecular oxygen is presented. The electrode comprises needle shaped maghemite nanorods firmly anchored to nitrogen doped carbon nanotubes, which in turn are grown on a conducting carbon paper that acts as efficient current collector. In 0.1 M KOH this hybrid electrode reaches a current density of 1 mA/cm(2) (geometric surface) at an overpotential of 362 mV performing high chronoamperometric stability. The electrochemical attributes point toward efficient catalytic processes at the surface of the maghemite nanorods, and demonstrate a very high surface area of the 3D electrode, as well as a firm anchoring of each active component enabling an efficient charge transport from the surface of the maghemite rods to the carbon paper current collector. The latter property also explains the good stability of our hybrid electrode compared to transition metal oxides deposited on conducting support such as fluorine doped tin oxide. These results introduce maghemite as efficient, stable and earth abundant oxygen evolution reaction catalyst, and provide insight into key issues for obtaining practical electrodes for oxygen evolution reaction, which are compatible with large scale production processes. 

Keyword
Nitrogen-doped carbon nanotubes, Maghemite, Hybrid catalyst, Water oxidation, 3D electrode
National Category
Materials Chemistry Other Chemistry Topics Other Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-130009 (URN)10.1016/j.ijhydene.2015.11.165 (DOI)000368955300005 ()
Available from: 2017-01-11 Created: 2017-01-11 Last updated: 2017-11-29Bibliographically approved
6. Comprehensive study of an earth-abundant bifunctional 3D electrode for efficient water electrolysis in alkaline medium
Open this publication in new window or tab >>Comprehensive study of an earth-abundant bifunctional 3D electrode for efficient water electrolysis in alkaline medium
Show others...
2015 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 7, no 51, 28148-28155 p.Article in journal (Refereed) Published
Abstract [en]

We report efficient electrolysis of both water splitting half reactions in the same medium by a bifunctional 3D electrode comprising Co3O4 nanospheres nucleated on the surface of nitrogen-doped carbon nanotubes (NCNTs) that in turn are grown on conductive carbon paper (CP). The resulting electrode exhibits high stability and large electrochemical activity for both oxygen and hydrogen evolution reactions (OER and HER). We obtain a current density of 10 mA/cm(2) in 0.1 M KOH solution at overpotentials of only 0.47 and 0.38 V for OER and HER, respectively. Additionally, the experimental observations are understood and supported by analyzing the Co3O4:NCNT and NCNT:CP interfaces by ab initio calculations. Both the experimental and the theoretical studies indicate that firm and well-established interfaces along the electrode play a crucial role on the stability and electrochemical activity for both OER and HER.

Place, publisher, year, edition, pages
Washington: American Chemical Society (ACS), 2015
Keyword
water splitting, bifunctional catalyst, oxygen evolution reaction, hydrogen evolution reaction, transition metal oxides, nitrogen-doped carbon nanotubes
National Category
Condensed Matter Physics Nano Technology
Identifiers
urn:nbn:se:umu:diva-117855 (URN)10.1021/acsami.5b10118 (DOI)000369448200021 ()26629887 (PubMedID)
Available from: 2016-03-16 Created: 2016-03-04 Last updated: 2017-11-30Bibliographically approved

Open Access in DiVA

fulltext(4004 kB)1811 downloads
File information
File name FULLTEXT01.pdfFile size 4004 kBChecksum SHA-512
0e142a85d91566f4c0ed990dd121102d894f7e234ee8cc2e373d4236c3c645288af5d65b0eacd4e3e9295868d4f893cc57f2768c6a9ed2ed42f01fc1ff855ed5
Type fulltextMimetype application/pdf
spikblad(151 kB)11 downloads
File information
File name SPIKBLAD01.pdfFile size 151 kBChecksum SHA-512
9380c70aa926041e302407809f1b9acab47598e21df85a6195a3c1add01fe8d718400e2f17dc85d4dcdd5b8a5aad3e2138a15a7db10bea21869195d69c61efe8
Type spikbladMimetype application/pdf

Search in DiVA

By author/editor
Sharifi, Tiva
By organisation
Department of Physics
Condensed Matter Physics

Search outside of DiVA

GoogleGoogle Scholar
Total: 1811 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 2071 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf