Tailoring the microenvironment in Fe-N-C electrocatalysts for optimal oxygen reduction reaction performance

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Fe-N-C electrocatalysts with FeN4 single atom sites are effective for oxygen reduction reaction (ORR), particularly in alkaline media.
• Enhancing the accessibility and microenvironment of FeN4 sites is crucial for improving ORR activity.

Purpose of the Study:

• To develop a simple synthetic strategy for Fe-N-C electrocatalysts with enhanced ORR activity.
• To improve the accessibility and tune the microenvironment of FeN4 sites.
• To investigate the structure-activity relationship for optimized ORR performance.

Main Methods:

• One-step pyrolysis of a Fe-containing zeolitic imidazolate framework with NaCl.
• Characterization of the hierarchically porous Fe-N-C electrocatalyst.
• Electrochemical evaluation of ORR performance in 0.1 mol L-1 KOH.

Main Results:

• A hierarchically porous Fe-N-C electrocatalyst with tailored FeN4 sites was synthesized.
• The catalyst exhibited slightly elongated Fe-N bond distances and reduced Fe charge.
• The porous structure enhanced mass transport, and the optimized microenvironment improved intermediate adsorption/desorption.
• High FeN4 site density (9.9 × 10^19 sites g-1) and turnover frequency (2.26 s-1) were achieved.
• Remarkable ORR performance with a low overpotential (half-wave potential of 0.90 V vs. RHE) was demonstrated.

Conclusions:

• The developed Fe-N-C electrocatalyst shows significant potential for ORR applications.
• The simple synthetic strategy effectively enhances FeN4 site accessibility and optimizes the microenvironment.
• This work provides insights into designing high-performance single-atom electrocatalysts for energy conversion reactions.