Identification of Durable and Non-Durable FeNx Sites in Fe-N-C Materials for Proton Exchange Membrane Fuel Cells

Jingkun Li (1) , Moulay Tahar Sougrati (1) , Andrea Zitolo (2) , James M Ablett (2) , Ismail Can Oğuz (1) , Tzonka Mineva (1) , Ivana Matanovic (3, 4) , Plamen Atanassov (5) , Ying Huang (5) , Iryna Zenyuk (5) , Andrea Di Cicco (6) , Kavita Kumar (7) , Laetitia Dubau (7) , Frédéric Maillard (7) , Goran Dražić (8) , Frederic Jaouen (1)

1 ICGM - Institut Charles Gerhardt Montpellier - Institut de Chimie Moléculaire et des Matériaux de Montpellier
2 SSOLEIL - Synchrotron SOLEIL
3 Theoretical Division [LANL]
4 CMEM - Center for Micro-Engineered Materials [Albuquerque]
5 UC Irvine - University of California [Irvine]
6 UNICAM - Università degli Studi di Camerino = University of Camerino
7 EIP - Electrochimie Interfaciale et Procédés
8 KI - National Institute of Chemistry [Llubljana]

While Fe-N-C materials are a promising alternative to platinum for catalyzing oxygen reduction in acidic polymer fuel cells, limited understanding of their operando degradation restricts rational approaches towards improved durability. Here we show that Fe-N-C catalysts initially comprising two distinct FeNx sites (S1 and S2) degrade via the transformation of S1 into iron oxides while the structure and number of S2 were unmodified. Structure-activity correlations drawn from end-of-test 57Fe Mössbauer spectroscopy reveal that both sites initially contribute to the ORR activity but only S2 significantly contributes after 50 h of operation. From in situ 57Fe Mössbauer spectroscopy in inert gas coupled to calculations of the Mössbauer signature of FeNx moieties in different electronic states, we identify S1 to be a high-spin FeN4C12 moiety and S2 a low- or intermediate spin FeN4C10 moiety. These insights lay the ground for rational approaches towards Fe-N-C cathodes with improved durability in acidic fuel cells.

Domaines: Chimie; Catalyse; Matériaux

Jingkun Li, Moulay Tahar Sougrati, Andrea Zitolo, James M Ablett, Ismail Can Oğuz, et al.. Identification of Durable and Non-Durable FeNx Sites in Fe-N-C Materials for Proton Exchange Membrane Fuel Cells. Nature Catalysis, 2020, 4, pp.10-19. ⟨10.1038/s41929-020-00545-2⟩. ⟨hal-02931434v2⟩