Nitrogen Electrocatalysis: Electrolyte Engineering Strategies to Boost Faradaic Efficiency.

Abstract

The electrochemical activation of dinitrogen at ambient temperature and pressure for the synthesis of ammonia has drawn increasing attention. The Faradaic Efficiency (FE) as well as ammonia yield in the electrochemical synthesis is far from reaching the requirement of industrial scale production. In aqueous electrolytes, the electron stealing hydrogen evolution reaction (HER) and poor solubility of nitrogen are the two major bottlenecks. As the electrochemical reduction of nitrogen involves proton-coupled electron transfer reaction, the rationally engineered electrolytes are required to boost FE and ammonia yield. In this review, we comprehensively summarize various electrolyte engineering strategies to boost the FE in aqueous and non-aqueous medium and suggest possible approach to further improve the performance. In aqueous medium, the performance can be improved by modulating the electrolyte pH, transport velocity of proton, and water activity. The other strategies involve the use of hybrid and water-in-salt electrolytes, ionic liquids, and non-aqueous electrolytes. The existing aqueous electrolytes are not ideal for industrial scale production. Suppression of HER and enhanced nitrogen solubility have been observed with hybrid and non-aqueous electrolytes. The engineered electrolytes are very promising though the electrochemical activation has several challenges. The outcome of lithium-mediated NRR with engineered non-aqueous electrolyte is highly encouraging.