Electrocatalytic Ammonia Oxidation by a Low-Coordinate Copper Complex

Area of Science:

• Electrochemistry
• Catalysis
• Inorganic Chemistry

Background:

• Ammonia oxidation to dinitrogen is crucial for utilizing ammonia as a fuel and hydrogen source.
• This process requires breaking strong N-H bonds and forming N-N bonds, presenting significant catalytic challenges.

Purpose of the Study:

• To report a novel β-diketiminato copper complex as a robust electrocatalyst for ammonia oxidation.
• To investigate the mechanism of ammonia oxidation mediated by the copper catalyst.

Main Methods:

• Electrochemical characterization including cyclic voltammetry (CV) and controlled potential electrolysis (CPE).
• Synthesis and characterization of a novel β-diketiminato copper complex.
• Density Functional Theory (DFT) analysis to elucidate reaction pathways and thermodynamic barriers.

Main Results:

• The synthesized copper complex ([Pr₂NN_F6]Cu^I-NH₃) efficiently catalyzes ammonia oxidation at a moderate overpotential (700 mV) with a high turnover frequency (TOF_max = 940 h^-1).
• The catalyst demonstrated excellent stability during prolonged electrolysis (>5 h).
• Mechanistic studies revealed the formation of a reactive copper(II)-amide intermediate, crucial for N-N bond formation, and identified electrocatalytically inactive species at high ammonia concentrations.

Conclusions:

• The reported copper complex is a robust and efficient electrocatalyst for ammonia oxidation to dinitrogen.
• Understanding the mechanistic pathway, including the role of copper-amide intermediates and the deactivation pathway at high ammonia concentrations, is key for catalyst design.
• This work provides a promising avenue for the development of catalysts for ammonia-based energy applications.