Single Atomic Cerium Sites with a High Coordination Number for Efficient Oxygen Reduction in Proton-Exchange Membrane Fuel Cells

Fe-N-C electrocatalysts, as a representative of platinum group metal-free (PGM-free) catalysts, exhibit a comparable oxygen reduction reaction (ORR) activity but insufficient stability to that of commercial Pt/C in proton-exchange membrane fuel cells (PEMFCs), due to the unavoidable Fenton's reactions. Herein, we report a hard-template approach to synthesize the rare-earth singlecerium-atom-doped metal-organic frameworks with a hierarchically macro-meso-microporous structure. Spherical aberration correction electron microscopy confirms the atomic dispersion of Ce sites. Additionally, X-ray absorption spectroscopy (XAS) was employed to further verify the coordination environment of Ce sites, which were stabilized by four-coordinated nitrogen atoms and six-oxygen atoms (Ce-N-4/O-6). The Ce sites were embedded in a hierarchically macromeso-microporous N-doped carbon (Ce SAS/HPNC) catalyst, which exhibits a half-wave potential of 0.862 V in ORR and the highest power density of 0.525 W cm(-2) under 2.0 bar H-2/O-2 in the fuel cell test.

Automated summary

The study introduces a hard-template method to synthesize rare-earth single cerium-atom-doped metal-organic frameworks with a hierarchically macro-meso-microporous structure, demonstrated by spherical aberration correction electron microscopy. The Ce sites embedded in the hierarchically macromeso-microporous N-doped carbon catalyst show high half-wave potential and power density in the oxygen reduction reaction.