Oxygen Reduction Reaction at Penta-Coordinated Co Phthalocyanines

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Cobalt phthalocyanines (CoPc) are studied as oxygen reduction reaction (ORR) electrocatalysts.
• Typically, CoPc facilitates a 2-electron ORR to peroxide, but a 4-electron pathway is preferred for fuel cells.

Purpose of the Study:

• To synthesize and investigate novel cobalt catalysts for enhanced 4-electron ORR.
• To understand the influence of axial ligands and in-plane substituents on ORR activity.

Main Methods:

• Synthesis of three CoN4 phthalocyanine catalysts with pyridine axial linkers on carbon nanotubes.
• Characterization using EPR and XPS spectroscopy.
• Electrochemical evaluation via ab initio calculations, Koutecky-Levich extrapolation, and Tafel plots.

Main Results:

• The pyridine axial linker was confirmed to increase Co-O2 binding energy, promoting the 4-electron ORR.
• Electron-withdrawing or donating residues on the phthalocyanine ligand did not further enhance catalyst activity due to pull-push electronic effects.

Conclusions:

• Cobalt phthalocyanine catalysts with pyridine axial linkers are effective for promoting the 4-electron ORR.
• Careful tuning of electronic properties is crucial for optimizing ORR electrocatalyst performance.