Phenol as proton shuttle and buffer for lithium-mediated ammonia electrosynthesis.

Area of Science:

• Electrochemistry
• Catalysis
• Materials Science

Background:

• Ammonia synthesis is vital for fertilizers and nitrogen compounds.
• Lithium-mediated nitrogen reduction reaction (Li-NRR) offers ambient ammonia production.
• Proton shuttles are critical for Li-NRR but lack established design principles.

Purpose of the Study:

• Establish design principles for effective proton shuttles in Li-NRR.
• Develop a general procedure to verify true proton shuttles.
• Identify superior proton shuttle candidates for practical Li-NRR systems.

Main Methods:

• Systematic evaluation of various proton shuttles in a continuous-flow reactor.
• Utilized hydrogen oxidation at the anode.
• Employed operando isotope-labeled mass spectrometry and mass transport modeling.

Main Results:

• Phenol emerged as the most effective proton shuttle, achieving 72% ± 3% Faradaic efficiency for ammonia.
• Phenol outperformed commonly used ethanol as a proton shuttle.
• Experimental evidence confirmed phenol's proton-shuttling capability.

Conclusions:

• Established design principles for effective proton shuttles in Li-NRR.
• Phenol is a highly promising proton shuttle for efficient ambient ammonia synthesis.
• This work advances the practical application of Li-NRR for sustainable ammonia production.