Abstract
Since a few years, non-precious metal catalysts with iron or cobalt as active centers show sufficient activity to be viable candidates as electrocatalysts for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFC). They can sustain substantial current densities when operated at low potentials. However, their stabilization at high cathode potentials, necessary for high energy efficiency, remains a daunting task. Here an Fe-N-C catalyst is stabilized over the whole potential range through functionalization with minute amounts of platinum. With the addition of 1 to 2 wt% Pt, the present Pt/Fe-N-C hybrid catalysts show a similar current density at 0.8 V than Fe-N-C but are much more stable during operation in PEMFC. Various characterization techniques, including CO stripping, demonstrate that platinum in these hybrid catalysts is ORR-inactive, not only initially but also after the PEMFC potentiostatic test. It is proposed that the present platinum species protects the Fe-based active sites from the ORR by-product H 2 O 2 , or reactive oxygen species produced from its reaction with surface Fe. This proof-of-concept paves the way for a new class of hybrid catalysts, where the activity and stability of Me-N-C catalysts can be independently addressed.