Oxygen reduction reaction (ORR) in acidic meida is crucial for the performance of proton exchange membrane fuel cell (PEMFC) technologies. Instead of platinum metals, using platinum-metal-group (PGM)-free catalysts remains a grand challenge in the field yet. In this talk, I will present a new type of atomic iron-dispersed carbon catalyst with homogeneous microstructure. The iron atoms were found atomically embedded into partially graphitized carbon. Due to the significantly improved uniformity and increased density of active sites, the ORR activity and stability of this new catalyst reached to a new milestone, approaching to the state of the art Pt/C catalysts in 0.5 M H2SO4 electrolyte. The novel catalyst is derived from a well-defined iron doped metal-organic framework precursor with ordered crystal structure through a single carbonization step in N2 atmosphere. Obtaining the optimal doping content of Fe into the MOF during the precursor synthesis played a key role in achieving the atomically dispersed iron morphology associated with the improvement of activity and stability. Unlike previous studied Fe-based catalysts, the particle size and shape of this catalyst were well-controlled and highly homogeneous and can be directly transferred from the morphology of Fe-doped MOF precursors. Notably, optimal iron doping content is crucial for activity and stability enhancement, which correlated to iron distribution, carbon structures, surface areas/porosity, and nitrogen doping. Doping high Fe content is desirable to provide more active sites. However, atomic iron tends to agglomerate and form clusters when Fe content is increased. Clearly, doped Fe content affects the critical nitrogen doping including the total content and doping position. This work provides evidence that superior ORR activity arises from atomically and homogenously dispersed FeNx active sites located in the carbon. The elucidation of structure-property correlations revealed that Fe content in the precursor is the foremost variable in controlling the synthetic chemistry of these catalysts, and affects various properties including particle size, porosity, graphitization, and nitrogen-doping. Most importantly, this work strongly supports the theoretical prediction that iron-based catalysts are able to achieve comparable catalytic activity of Pt in the highly challenging environment of acid media.

Atomic iron-dispersed carbon electrocatalysts for oxygen reduction in challenging acid

254th National Meeting (2017)

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