Journal
JOURNAL OF POWER SOURCES
Volume 490, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.jpowsour.2021.229487
Keywords
Fe/N/C; ORR; Fe-N-pyridinic; Fe-N-pyrrolic; NEXAFS; Surface sites
Funding
- PEGASUS project - European Union [JTI-FCH-2017-1, 779550]
- Spanish Ministry of Economy and Competitiveness (MINECO) [ENE2016-77055-C3-3-R]
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The study found different types of FeNxCy moieties in Fe/C/N catalysts, which evolve during the oxygen reduction reaction (ORR), with pyridinic moieties playing a significant role in the ORR activity.
The nature and evolution of FeNxCy moieties in Fe/C/N catalysts has been studied by analysing Fe and N environments. TEM and Fe-XAS reveal the presence of FeNx moieties and Fe3C particles in the fresh catalyst. NEXAFS reveals the presence of two groups of (Fe)NxCy ensembles, namely (Fe)N-x-pyridinic and (Fe)N-x-pyrrolic. The architecture of the FeNxCy ensembles and their evolution during the ORR has been analysed by XAS, NEXAFS, and identical locations TEM. NxCy, FeNxCy and Fe3C species are partially removed during the ORR, resulting in the formation of Fe2O3 and Fe3O4 particles with different morphologies. The process is more severe in acid electrolyte than in alkaline one. (Fe)N-x-pyrrolic moieties are the main ones in the fresh catalysts, but (Fe) N-x-pyridinic groups are more stable after the ORR. The correlation between the evolution of the ORR activity and that of the FeNxCy ensembles indicates that FeNx-pyridinic ensembles are responsible for the ORR activity.
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