Meso/Microporous Single-Atom Catalysts Featuring Curved Fe-N₄ Sites Boost the Oxygen Reduction Reaction Activity

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Zeolitic-imidazolate frameworks (ZIFs) are precursors for Fe-N/C catalysts.
• Current ZIF-derived catalysts are microporous, limiting mass transport.
• Improved catalysts are needed for Zn-air batteries (ZABs) and proton exchange fuel cells (PEMFCs).

Purpose of the Study:

• To synthesize a novel meso/microporous Fe-N/C material with curved Fe-N4 active sites.
• To evaluate its performance as an electrocatalyst for oxygen reduction reaction (ORR).
• To demonstrate its application in ZABs and PEMFCs.

Main Methods:

• Pyrolysis of hemin-modified ZIF films on ZnO nanorods.
• Synthesis of atomically dispersed meso/microporous Fe-N/C (FeSA-N/TC).
• Density functional theory (DFT) calculations to understand active site mechanism.

Main Results:

• FeSA-N/TC exhibits curved Fe-N4 active sites, enhancing ORR.
• Achieved half-wave potentials of 0.925 V (alkaline) and 0.825 V (acidic).
• Demonstrated high peak power densities in H2-O2 PEMFCs (1100 mW cm-2) and ZABs (228 mW cm-2).

Conclusions:

• The novel FeSA-N/TC catalyst shows superior ORR activity.
• Meso/microporosity and curved Fe-N4 sites improve mass transport and catalytic performance.
• FeSA-N/TC is a promising electrocatalyst for ZABs and PEMFCs.