Ammonia Oxidation with a Ruthenium Polypyridyl Complex: Mechanism-Guided Approach to Low Overpotential...

Area of Science:

• Inorganic Chemistry
• Electrochemistry
• Sustainable Energy

Background:

• Ammonia is a promising zero-carbon fuel, necessitating efficient catalysts for its sustainable utilization.
• Understanding the ammonia oxidation reaction (AOR) mechanism is crucial for developing effective energy carriers.

Purpose of the Study:

• To investigate a ruthenium complex, [RuII(TPA)-(NH3)2]-(PF6)2 (1-(PF6)2), as a homogeneous electrocatalyst for AOR.
• To elucidate the reaction mechanism, identify key intermediates, and determine the catalytic cycle.

Main Methods:

• Electrochemical studies and electrolysis.
• Density Functional Theory (DFT) computations.
• Spectroscopic analysis and 15N labeling experiments.

Main Results:

• The ruthenium complex 1-(PF6)2 acts as an efficient AOR electrocatalyst, producing N2 and H2 at a moderate potential (0.96 V).
• The catalytic cycle involves deprotonation as the rate-determining step and intermolecular N-N coupling of an amido intermediate.
• Complex 2-(PF6)2 is a catalytically active intermediate, while XI-(PF6)2 is an off-cycle product.

Conclusions:

• A detailed catalytic cycle for AOR has been proposed, highlighting intermolecular coupling at an early amido stage.
• The developed ruthenium catalyst circumvents high metal oxidation states, offering a low overpotential for ammonia electro-oxidation.
• This research provides insights into designing efficient catalysts for sustainable ammonia-based energy systems.