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, Vol. 6, no 10, 8904-8912 p.Article in journal (Refereed) Published
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.
nitrogen-doped carbon nanotubes, nitrogen functionalities, X-ray photoelectron spectroscopy, electrochemistry, cyclic voltammetry, oxygen reduction reactions
Physical Sciences Chemical Sciences Nano Technology
IdentifiersURN: urn:nbn:se:umu:diva-61776DOI: 10.1021/nn302906rISI: 000310096100049OAI: oai:DiVA.org:umu-61776DiVA: diva2:572459