Electrocatalytic Ammonia Oxidation by Pyridyl-Substituted Ferrocenes

Area of Science:

• Electrochemistry
• Sustainable Energy
• Catalysis

Background:

• Ammonia (NH3) is a key carbon-free fuel derived from sustainable sources.
• Efficient electrocatalysts are crucial for ammonia oxidation in sustainable energy production.

Purpose of the Study:

• To develop and characterize Earth-abundant iron-based molecular complexes for electrocatalytic ammonia oxidation.
• To elucidate the mechanism of ammonia oxidation facilitated by these catalysts.

Main Methods:

• Electrochemical studies of ferrocene derivatives with pyridine arms in DMSO.
• Experimental and computational investigations of the catalytic mechanism.
• Analysis of proton-coupled electron transfer (PCET) and H-bonding interactions.

Main Results:

• Facile ammonia oxidation achieved with modest overpotentials (770-820 mV) and turnover frequencies (125-560 h-1).
• Demonstrated a PCET mechanism involving H-bonding activation of ammonia.
• Identified intermediate amidyl radical formation and subsequent dimerization to hydrazine.

Conclusions:

• Developed a general strategy for ammonia oxidation using H-bonding to activate the N-H bond for PCET.
• Iron-based catalysts offer a promising route for sustainable ammonia fuel applications.
• The generated hydrazine is readily oxidized to nitrogen, indicating a complete catalytic cycle.