Hierarchical Porous Fe₃C@Fe-N-C Catalysts from Tannin-Fe(III) Complexes for Efficient Oxygen Reduction

Area of Science:

• Materials Science
• Electrochemistry
• Renewable Energy

Background:

• Developing cost-effective and high-performance electrocatalysts is crucial for advancing low-temperature fuel cells.
• Metal-nitrogen-doped carbons (M-N-C) are promising catalysts, but their synthesis often relies on expensive precursors.
• Mimosa tannin offers an abundant, renewable source for designing advanced M-N-C materials.

Purpose of the Study:

• To synthesize a novel Fe-N-C single-atom catalyst using mimosa tannin as a renewable carbon source.
• To investigate the catalytic performance of the tannin-derived Fe-N-C material for oxygen reduction reaction (ORR).
• To evaluate the catalyst's efficacy in practical hydrogen polymer-electrolyte membrane fuel cells.

Main Methods:

• Coordination of mimosa tannin with Fe(III) and use of Pluronic F127 as a surfactant and promoter.
• Carbonization of the tannin-Fe(III) complex in the presence of urea to form Fe-N-C structures.
• Electrochemical characterization of the catalyst in alkaline and acidic media and testing in fuel cell devices.

Main Results:

• The synthesized catalyst features Fe3C nanoparticles encapsulated on a Fe-N-C single-atom catalyst with hierarchical porosity.
• Optimal catalyst composition achieved high ORR half-wave potentials (0.87 V in alkaline, 0.74 V in acidic electrolytes).
• Demonstrated strong performance in polymer-electrolyte membrane fuel cells, reaching peak power densities of 242 mW cm-2 (alkaline) and 200 mW cm-2 (acidic).

Conclusions:

• Mimosa tannin is a viable and sustainable precursor for fabricating high-performance Fe-N-C electrocatalysts.
• The developed catalyst exhibits excellent ORR activity and stability in both alkaline and acidic environments.
• This approach provides a pathway for designing renewable M-N-C electrodes for electrochemical energy applications.