Is Ethanol Essential for the Lithium-Mediated Nitrogen Reduction Reaction?

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• Decentralized ammonia synthesis is crucial for sustainable agriculture and industry.
• Lithium-mediated nitrogen reduction (Li-NRR) offers a promising renewable energy-driven pathway.
• Organic electrolytes and proton shuttles like ethanol are commonly employed to enhance Li-NRR efficiency and suppress side reactions.

Purpose of the Study:

• To elucidate the specific role of ethanol as a proton shuttle in Li-NRR within a tetrahydrofuran-based electrolyte.
• To investigate the necessity of ethanol for ammonia synthesis and solid-electrolyte interphase (SEI) formation.
• To explore alternative proton shuttle mechanisms and their impact on Li-NRR electrochemistry.

Main Methods:

• Electrochemical experiments designed to isolate the functions of ethanol.
• Electrochemical quartz crystal microbalance (EQCM) for in-situ monitoring of SEI formation during lithium plating.
• Chemical batch synthesis of ammonia coupled with real-time mass spectrometry.

Main Results:

• Ethanol is found to be essential for forming a stable solid-electrolyte interphase (SEI) but not directly for ammonia synthesis.
• Electrochemical quartz crystal microbalance (EQCM) highlights the critical role of SEI formation at the initial stage of lithium deposition.
• Alternative species were confirmed to effectively shuttle protons from anode to cathode, enabling ammonia synthesis without ethanol.

Conclusions:

• The findings challenge the established necessity of ethanol in Li-NRR, suggesting alternative proton sources are viable.
• The study underscores the importance of SEI properties in Li-NRR performance.
• Further investigation into the fundamental electrochemical mechanisms of Li-NRR is warranted, considering the potential for non-ethanol-mediated pathways.