Reduced formation of peroxide and radical species stabilises iron-based hybrid catalysts in polymer electrolyte membrane fuel cells

Abstract The incorporation of Pt into an iron-nitrogen-carbon (FeNC) catalyst for the oxygen reduction reaction (ORR) was recently shown to enhance catalyst stability without Pt directly contributing to the ORR activity. However, the mechanistic origin of this stabilisation remained obscure. It is established herein with rotating ring disc experiments that the side product, H2O2, which is known to damage FeNC catalysts, is suppressed by the presence of Pt. The formation of reactive oxygen species is additionally inhibited, independent of intrinsic H2O2 formation, as determined by electron paramagnetic resonance. Transmission electron microscopy identifies an oxidised Fe-rich layer covering the Pt particles, thus explaining the inactivity of the latter towards the ORR. These insights develop understanding of FeNC degradation mechanisms during ORR catalysis, and crucially establish the required properties of a precious metal free protective catalyst to improve FeNC stability in acidic media.