Simultaneously Integrate Iron Single Atom and Nanocluster Triggered Tandem Effect for Boosting Oxygen...

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Atomically nitrogen-coordinated iron (FeN-C) catalysts are promising alternatives to precious metals for the oxygen reduction reaction (ORR).
• Current FeN-C catalysts often exhibit suboptimal performance due to symmetric charge distribution around iron sites, hindering catalytic efficiency.
• Tailoring the microenvironment of the central iron atom is crucial for enhancing FeN-C catalytic activity but remains a significant challenge.

Purpose of the Study:

• To develop novel N/S co-doped porous carbon materials with precisely engineered iron active sites for improved ORR catalysis.
• To investigate the synergistic effects of atomically dispersed FeN4 sites and adjacent Fe nanoclusters in modulating the electronic structure of iron centers.
• To demonstrate the enhanced catalytic performance of these engineered catalysts in electrochemical applications, specifically Zn-air batteries.

Main Methods:

• Rational synthesis of N/S co-doped porous carbons integrated with Fe-active sites (FeSA-FeNC@NSC).
• Systematic characterization using synchrotron X-ray absorption spectroscopy to identify atomically dispersed FeN4 and Fe nanoclusters.
• Theoretical calculations to elucidate the electronic structure modifications and reaction mechanisms at the Fe centers.
• Electrochemical testing of the FeSA-FeNC@NSC catalysts for ORR activity and performance in Zn-air batteries.

Main Results:

• The FeSA-FeNC@NSC material was successfully synthesized, featuring both FeN4 sites and Fe nanoclusters.
• Synchrotron X-ray absorption spectroscopy confirmed the presence and nature of the Fe active sites.
• Theoretical calculations revealed that contiguous S atoms and Fe nanoclusters break the symmetry of FeN4, optimizing Fe 3d orbitals and accelerating O-O bond cleavage in OOH* intermediates.
• The FeSA-FeNC@NSC catalyst exhibited a superior ORR half-wave potential of 0.90 V, surpassing that of commercial Pt/C (0.87 V).
• Zn-air batteries utilizing FeSA-FeNC@NSC demonstrated high power densities of 259.88 mW cm⁻² (liquid) and 55.86 mW cm⁻² (all-solid-state flexible).

Conclusions:

• The study presents an effective strategy for modulating the microenvironment of single atomic centers through a tandem effect of FeN4 and Fe nanoclusters.
• N/S co-doping and the presence of Fe nanoclusters synergistically enhance ORR activity by optimizing the electronic structure of Fe active sites.
• The developed FeSA-FeNC@NSC catalysts show significant potential for replacing precious metal catalysts in energy conversion devices like Zn-air batteries.