title: Unveiling N-protonation and anion-binding effects on Fe/N/C-catalysts for O2reduction in PEM fuel cells.
abstract: The high cost of proton-exchange-membrane fuel cells would be considerably reduced if platinumbased catalysts were replaced by iron-based substitutes, which have recently demonstrated comparable activity for oxygen reduction, but whose cause of activity decay in acidic medium has been elusive. Here, we reveal that the activity of Fe/N/C-catalysts prepared through a pyrolysis in NH3is mostly imparted by acid-resistant FeN4-sites whose turnover frequency for the O2reduction can be regulated by fine chemical changes of the catalyst surface. We show that surface N-groups protonate at pH 1 and subsequently bind anions. This results in decreased activity for the O2reduction. The anions can be removed chemically or thermally, which restores the activity of acid-resistant FeN4-sites. These results are interpreted as an increased turnover frequency of FeN4-sites when specific surface N-groups protonate. These unprecedented findings provide new perspective for stabilizing the most active Fe/N/C-catalysts known to date.
authors.affiliation: Institut National de la Recherche Scientifique, Énergie, Matériaux et Télécommunications, Varennes, Québec, J3X 1S2, Canada.
authors.forename: Juan
authors.initials: J
authors.lastname: Herranz
authors.forename: Frédéric
authors.initials: F
authors.lastname: Jaouen
authors.forename: Michel
authors.initials: M
authors.lastname: Lefèvre
authors.forename: Ulrike I
authors.initials: UI
authors.lastname: Kramm
authors.forename: Eric
authors.initials: E
authors.lastname: Proietti
authors.forename: Jean-Pol
authors.initials: JP
authors.lastname: Dodelet
authors.forename: Peter
authors.initials: P
authors.lastname: Bogdanoff
authors.forename: Sebastian
authors.initials: S
authors.lastname: Fiechter
authors.forename: Irmgard
authors.initials: I
authors.lastname: Abs-Wurmbach
authors.forename: Patrick
authors.initials: P
authors.lastname: Bertrand
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Arruda
authors.forename: Sanjeev
authors.initials: S
authors.lastname: Mukerjee
keywords: Electrocatalysis; acid; degradation; durability; non precious metal; oxygen reduction