Challenges and opportunities for nitrogen reduction to ammonia on transitional metal nitrides via Mars-van Krevelen mechanism

Ammonia (NH3) has a myriad of applications ranging from fertilizers to value-added chemicals and fuels. More energy-efficient and environmentally friendly approaches are needed to carry out the reduction of nitrogen (N2) to NH3, and, in principle, this can be done through electrochemical N2 reduction reaction (NRR). Limited progress has been made in NRR because of the sluggish reaction kinetics and the low selectivity of N2 toward NH3. Among the various catalysts explored, transition metal nitrides (TMNs) stand out because of their favorable Mars-van Krevelen mechanism. In this perspective, we review the critical work in the field, highlighting the main limitations to be surmounted (i.e., kinetic and transport limitations, optimization criteria, and long-term stability) and the different materials and methods (i.e., catalyst surface engineering, active site modification, and mechanistic studies) that have been proposed to overcome these limitations. Finally, opportunities for future scientific breakthroughs in the field are highlighted and discussed.