Same FeN4 Active Site, Different Activity: How Redox Peaks Control Oxygen Reduction on Fe Macrocycles.

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Macrocycles exhibit high activity for electrochemical oxygen reduction in alkaline media.
• Significant variations in activity and selectivity exist among macrocycles with similar FeNx active sites, lacking clear quantitative understanding.

Purpose of the Study:

• To systematically investigate the factors influencing the performance of iron macrocycles in oxygen reduction reactions.
• To elucidate the differences between various macrocycle structures and their impact on catalytic activity and selectivity.

Main Methods:

• Electrochemical techniques
• operando spectroscopy
• Density functional theory (DFT) simulations

Main Results:

• Identified two distinct families of iron macrocycles for oxygen reduction.
• Family 1: Weak *OH binding, one voltammetric peak, high peroxide selectivity.
• Family 2: Near-optimal *OH binding, two voltammetric peaks, minimal peroxide production.

Conclusions:

• The study proposes three mechanisms explaining the observed differences between the two macrocycle families.
• Understanding these differences is crucial for optimizing the activity of pyrolyzed FeNx catalysts.