Nitrogen-doped carbon catalysts derived from ionic liquids in the presence of transition metals for the oxygen reduction reaction
•Ionic liquids are promising precursors for nitrogen-doped carbon catalyst for ORR.•Use of transition metal in the pyrolysis of IL is important for high ORR activity.•The graphitic-N content in the sp2-carbon network is key factor for high ORR.•Co is an effective metal compared to Ni for nitrogen-doped carbon catalyst.
Nitrogen-doped carbon catalysts for the oxygen reduction reaction (ORR) were synthesized by the pyrolysis of ionic liquids (IL), which are precursors of both nitrogen and carbon, using a silica hard template in the presence of a transition metal. From the linear sweep voltammogram recorded in an acidic solution, the ORR activity of the nitrogen-doped carbon catalysts increased significantly after the addition of the transition metal during the pyrolysis of the IL. From XPS-N 1s analysis, the introduction of the transition metal positively contributes to the formation of graphitic-N, which is known to be an active site for the ORR. The results of XPS-C 1s suggest a strong correlation between the sp2-carbon network and the ORR activity. Co is a more effective metal compared to Ni due to the creation of a higher degree of sp2-carbon networks for fast electron transfer during the ORR. Based on the quantitative analysis of the experimental results, the IL is a promising precursor for nitrogen-doped carbon catalysts, and the addition of a transition metal is essential for improved activity of the ORR.
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Journal: Applied Catalysis B: Environmental - Volumes 158–159, October 2014, Pages 355–360