Oxygen Coordination on Fe-N-C to Boost Oxygen Reduction Catalysis

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Iron-nitrogen-carbon (Fe-N-C) catalysts are crucial for oxygen reduction reactions (ORR).
• The catalytic activity of Fe-N-C catalysts is highly dependent on the coordination environment of the iron (Fe) center.
• Precise atomic-level control over these coordination environments is challenging but essential for optimizing catalyst performance.

Purpose of the Study:

• To thoroughly investigate the atomic-level structure and coordination environment of Fe-N-C catalysts for ORR.
• To elucidate the role of specific moieties, such as O-Fe-N2C2, in determining catalytic activity.
• To understand how coordination environments direct the catalytic pathways in single-atom or single-site catalysts.

Main Methods:

• Advanced synchrotron X-ray characterizations to probe the catalyst structure.
• Theoretical modeling and computational simulations to understand reaction mechanisms.
• Combined experimental and theoretical approaches for comprehensive analysis.

Main Results:

• Atomically dispersed Fe-N-C catalysts with O-Fe-N2C2 moieties were synthesized and studied.
• The iron center within the O-Fe-N2C2 moiety was identified as penta-coordinated.
• Energetically optimized ORR pathways were mapped on these well-defined O-Fe-N2C2 sites.
• Evidence suggests that both the central metal atom and coordinating atoms actively participate in the catalytic cycle.

Conclusions:

• The penta-coordinated O-Fe-N2C2 moiety is a critical active site for ORR in Fe-N-C catalysts.
• Understanding and controlling the coordination environment is vital for designing highly active single-atom or single-site catalysts.
• The entire coordination sphere, not just the central metal atom, plays a significant role in catalysis.