Identification of Predominant Active Sites in a Platinum Group Metal (PGM)-free Catalyst for Polymer Electrolyte Fuel Cells

Identification of Predominant Active Sites in a Platinum Group Metal (PGM)-free Catalyst for Polymer Electrolyte Fuel Cells

Scientific Achievement

Active site(s) in a high-performance PGM-free Fe-N-C catalyst are visualized with scanning transmission electron microscopy (STEM)

a) Annular dark field (ADF)-STEM image of individual iron atoms associated with exposed basal plane edges of graphitic domains, consistent with the predominant “edge-hosted FeN4” sites identified in (CM+PANI)-Fe-N-C PGM-free catalyst. (b) ADF-STEM image of individual iron atoms embedded in few-layer graphene, consistent with less numerous “bulk-hosted FeN4” sites. Model shows the zigzag edge-hosted FeN4 structure with an OH ligand (N: blue, Fe: yellow, O: red, and H: white) (hi-res image)
and computationally correlated with specific lattice-level carbon structures.

Significance and Impact

The development of high-performance and durable PGM-free catalysts as an alternative to expensive Pt-based electrocatalysts can enable the widespread implementation of fuel-cell powered vehicles.

Research Details

– (CM+PANI)-Fe-C catalyst synthesized from cyanamide (CM), polyaniline (PANI), and iron (III) chloride.
– Aberration-corrected STEM imaging, quantitative EELS, and quantum chemistry calculations confirm zigzag edge-hosted FeN4 spontaneously ligated with OH lead to highly ORR-active structures.
 
H.T. Chung, D.A. Cullen, D. Higgins, B.T. Sneed, E.F. Holby, K.L. More, and P. Zelenay, Science 357, 479 (2017).  DOI: 10.1126/science.aan2255

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