Efficient Ammonia Electrosynthesis from Nitrate on Strained Ruthenium Nanoclusters

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• The Haber-Bosch process, while crucial for ammonia synthesis, requires high temperatures and pressures.
• Low-temperature ammonia synthesis is desirable for energy efficiency and reduced environmental impact.
• Existing methods like nitrogen (N₂) electroreduction face challenges with low production rates, current densities, and selectivity.

Purpose of the Study:

• To investigate nitrate electroreduction as a viable low-temperature ammonia synthesis pathway.
• To enhance ammonia production rate and selectivity using strained ruthenium nanoclusters.
• To elucidate the catalytic mechanism responsible for improved ammonia synthesis.

Main Methods:

• Electrochemical synthesis of ammonia from nitrate reduction at room temperature.
• Utilizing strained ruthenium (Ru) nanoclusters as catalysts.
• Characterization of catalyst structure and electrochemical performance.
• Mechanistic studies involving hydrogen radicals and intermediates.

Main Results:

• Achieved a high ammonia production rate of 5.56 mol g_cat^-1 h^-1, surpassing the Haber-Bosch process.
• Demonstrated sustained 100% ammonia-evolving selectivity at high current densities (>120 mA cm^-2) for 100 hours.
• Identified hydrogen radicals, generated by suppressed H-H dimerization, as key intermediates for efficient nitrate-to-ammonia conversion.
• Attributed catalyst stability to robust subsurface Ru-O coordination.

Conclusions:

• Room-temperature nitrate electroreduction catalyzed by strained ruthenium nanoclusters is a highly efficient and selective method for ammonia synthesis.
• The unique catalytic activity stems from strain-induced generation of hydrogen radicals, lowering kinetic barriers.
• This approach offers a promising alternative to the Haber-Bosch process for sustainable, low-temperature ammonia production.