Fe–N–C/Fe nanoparticle composite catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells

Replacing Pt-based catalysts with cost-effective, highly efficient, and durable platinum group metal-free catalysts for the oxygen reduction reaction (ORR) is crucial for commercializing hydrogen fuel cells. Herein, we present a highly active Fe-N-C electrocatalyst that contains both Fe nanoparticles and FeN_x active sites derived from an Fe-doped carbonized zeolitic imidazolate framework (ZIF-8). It is found that adjusting the doping amount of Fe in the Fe-doped ZIF-8 precursor alters the morphology of the catalyst after heat treatment. The Fe-N-C-300 composite catalyst with the optimized Fe doping amount exhibits excellent activity, good stability, and remarkable methanol tolerance in the challenging acid environment. This study reveals that a suitable amount of Fe nanoparticles in the catalyst can alter the structure of the FeN_x active moieties and increase three-phase boundaries to boost the mass transport, thus leading to improved fuel cell performance. This will have implications for using Fe-N-C catalysts in real applications, as the formation of Fe NPs during the synthesis and reaction is almost inevitable.