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Water Increases the Faradaic Selectivity of Li-Mediated Nitrogen Reduction
Matthew Spry1, Olivia Westhead1, Romain Tort2
1Department of Materials, Imperial College London, Prince Consort Road, South Kensington, London, SW7 2AZ, U.K.
ACS Energy Letters
|February 23, 2023
Summary
Adding trace water to lithium-mediated systems significantly boosts nitrogen to ammonia conversion selectivity. This discovery enhances ammonia synthesis efficiency under ambient conditions, highlighting sensitivity to experimental parameters.
Area of Science:
- Electrochemistry
- Catalysis
- Materials Science
Background:
- Lithium-mediated systems can convert nitrogen to ammonia under ambient conditions.
- Electrolyte additives can influence the efficiency of nitrogen reduction reactions.
- Prior literature suggested water inhibits nitrogen reduction.
Purpose of the Study:
- To investigate the effect of water as an electrolyte additive on lithium-mediated nitrogen to ammonia conversion.
- To optimize conditions for improved Faradaic selectivity in nitrogen reduction.
- To understand the mechanism behind water's influence on the reaction.
Main Methods:
- Electrochemical nitrogen reduction experiments using a lithium-mediated system.
- Systematic variation of water and LiClO4 salt concentrations.
- X-ray photoelectron spectroscopy (XPS) for surface analysis.
Main Results:
- Trace amounts of water dramatically improved the Faradaic selectivity of N2 reduction to NH3.
- Optimal water concentration (35.9 mM) and LiClO4 concentration (0.8 M) yielded a Faradaic efficiency of 27.9 ± 2.5%.
- XPS analysis indicated the formation of Li2O in the solid electrolyte interphase, correlating with improved efficiency.
Conclusions:
- Water, contrary to previous reports, acts as a beneficial electrolyte additive in lithium-mediated ammonia synthesis.
- The formation of Li2O in the solid electrolyte interphase is crucial for enhanced selectivity.
- Lithium-mediated nitrogen reduction is highly sensitive to subtle changes in experimental conditions, particularly water concentration.
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