Recent progress and prospects in electroreduction of nitrogen to ammonia in non-aqueous electrolytes

Ammonia production, mostly for use in fertilizers, currently consumes up to 2% of the world's energy production and accounts for more than 1.6% of global CO2 emissions. Hence, it is essential to develop a sustainable and eco-friendly process for NH3 synthesis. To date, various synthetic techniques have been developed under mild operation conditions. Among them, electrochemical nitrogen reduction reaction (ENRR) allows the direct conversion of atmospheric N2 into NH3 from renewables, offering various advantages, So far, most ENRR have been carried out in aqueous electrolytes. However the faradaic efficiency is usually low in such electrolytes, because water or proton reduction to hydrogen competes with nitrogen reduction. Compared to aqueous electrolytes, non-aqueous electrolytes show high electrochemical stability, increased solubility of N2, high selectivity, promoting the ENRR over hydrogen evolution-reactions, hence improving Faradaic efficiency. However, a comprehensive understanding of ENRR in nonaqueous electrolytes remains inadequate, and challenges such as poor selectivity, low current density, and low energy efficiency still remain in practical implementation. In this review, we summarize the recent progress of ENRR in nonaqueous electrolytes. Some technical challenges arising in this field are highlighted and assessed. In the final part, the perspectives are proposed for future research and commercial practice.