Manganese deception on graphene and implications in catalysis

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Metal-free graphene is explored for oxygen reduction reaction (ORR) catalysis.
• Varied ORR activity and potential metal contamination complicate understanding of "metal-free" catalysts.

Purpose of the Study:

• To investigate the true origin of ORR catalytic activity in graphene-based materials.
• To elucidate the role of trace elements in metal-free graphene catalysts.

Main Methods:

• High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM)
• X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS)
• Trace elemental analysis

Main Results:

• ORR activity is attributed to trace manganese, not the graphene itself.
• Optimal ORR performance (0.94 V onset potential) achieved with mononuclear manganese in defective graphene.
• Identified trace metals can significantly influence perceived catalyst performance.

Conclusions:

• The catalytic activity in "metal-free" graphene is often due to trace metal impurities.
• Designing single-atom catalysts with specific coordination chemistry is key for enhanced ORR performance.