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Active sites of nitrogen-doped carbon materials for oxygen reduction reaction clarified using model catalysts

Science  22 Jan 2016:
Vol. 351, Issue 6271, pp. 361-365
DOI: 10.1126/science.aad0832

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The right kind of dopant

The oxygen reduction reaction is an important step in fuel cells and other electrochemical processes but is still largely dependent on precious metal-containing catalysts. Recently explored alternatives include carbon materials that are doped with different, preferably non-precious metal, atoms. Guo et al. studied model graphite catalysts to try to understand the role of nitrogen doping and to elucidate the active catalytic sites. A nitrogen atom bound to two carbons formed an active catalyst site with an activity rivaling that of N-doped graphene catalysts.

Science, this issue p. 361

Abstract

Nitrogen (N)–doped carbon materials exhibit high electrocatalytic activity for the oxygen reduction reaction (ORR), which is essential for several renewable energy systems. However, the ORR active site (or sites) is unclear, which retards further developments of high-performance catalysts. Here, we characterized the ORR active site by using newly designed graphite (highly oriented pyrolitic graphite) model catalysts with well-defined π conjugation and well-controlled doping of N species. The ORR active site is created by pyridinic N. Carbon dioxide adsorption experiments indicated that pyridinic N also creates Lewis basic sites. The specific activities per pyridinic N in the HOPG model catalysts are comparable with those of N-doped graphene powder catalysts. Thus, the ORR active sites in N-doped carbon materials are carbon atoms with Lewis basicity next to pyridinic N.

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