Jingkun Li (1,9), 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), Frédéric Jaouen (1)
Nature Catalysis, 4, January 2021: 10–19. DOI: 10.1038/s41929-020-00545-2

Keywords

Electrocatalysis; Energy; Fuel cells; Heterogeneous catalysis

Abstract

While Fe–N–C materials are a promising alternative to platinum for catalysing the oxygen reduction reaction 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 oxygen reduction reaction activity but only S2 substantially 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 groundwork for rational approaches towards Fe–N–C cathodes with improved durability in acidic fuel cells.

How Our Software Was Used

Dragonfly was used to do the volume-rendering structure and analysis of X-ray images.

Author Affiliation

(1) Institut Charles Gerhardt Montpellier, UMR 5253, CNRS, Université Montpellier, ENSCM, Place Eugène Bataillon, Montpellier, France.
(2) Synchrotron SOLEIL, L’orme des Merisiers, BP 48 Saint Aubin, Gif-sur-Yvette, France.
(3) The Department of Chemical and Biological Engineering, Center for Micro-Engineered Materials (CMEM), University of New Mexico, Albuquerque, NM, USA.
(4) Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM, USA.
(5) Department of Chemical and Biomolecular Engineering, National Fuel Cell Research Center, University of California Irvine, Irvine, CA, USA.
(6) School of Science and Technology, Physics Division, University of Camerino, Camerino, MC, Italy.
(7) University of Grenoble Alpes, University of Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, Grenoble, France.
(8) Department of Materials Chemistry, National Institute of Chemistry, Ljubljana, Slovenia.
(9) School of Chemical Engineering and Technology, Tianjin University, Tianjin, China.