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

Abstract

The lithium-mediated nitrogen reduction reaction (Li-NRR) is a promising method for decentralized ammonia synthesis using renewable energy. An organic electrolyte is utilized to combat the competing hydrogen evolution reaction, and lithium is plated to activate the inert N2 molecule. Ethanol is commonly used as a proton shuttle to provide hydrogen to the activated nitrogen. In this study, we investigate the role of ethanol as a proton shuttle in an electrolyte containing tetrahydrofuran and 0.2 M lithium perchlorate. Particularly designed electrochemical experiments show that ethanol is necessary for a good solid-electrolyte interphase but not for the synthesis of ammonia. In addition, electrochemical quartz crystal microbalance (EQCM) demonstrates that the SEI formation at the onset of lithium plating is of specific importance. Chemical batch synthesis of ammonia combined with real-time mass spectrometry confirms that protons can be shuttled from the anode to the cathode by other species even without ethanol. Moreover, it raises questions regarding the electrochemical nature of Li-NRR. Finally, we discuss electrolyte stability and electrochemical electrode potentials, highlighting the role of ethanol on electrolyte degradation.