Abstract
Fe-N-C catalysts with high O2 reduction performance is crucial for displacing Pt in low temperature fuel cells. However, insufficient understanding of which reaction steps are catalyzed by what sites limits their progress. Here, we investigated the nature of sites active toward H2O2 reduction, a key intermediate during indirect O¬2 reduction and a source of deactivation in fuel cell. Catalysts comprising different relative contents of FeNxCy moieties and Fe particles encapsulated in N-doped carbon layers (0-100 %) show that both types of sites are active, although moderately, toward H2O2 reduction. In contrast, N-doped carbons free of Fe and Fe particles exposed to the electrolyte are inactive. When catalyzing the ORR, FeNxCy moieties are more selective than Fe particles encapsulated in N-doped carbon. These novel insights offer rational approaches for more selective and therefore more durable Fe-N-C catalysts