Atomic-level reactive sites for electrocatalytic nitrogen reduction to ammonia under ambient conditions

Ammonia (NH3) is an integral part to modern agriculture and industry. As an economical and sustainable process to convert nitrogen to NH3 under ambient conditions, the electrocatalytic nitrogen reduction reaction (NRR) strategy has attracted considerable attention in recent years. The fabrication of atomic-level reactive sites provides an opportunity to develop novel atomic-scale catalysts with excellent electrocatalytic NRR performance. In particular, the design of atomic-level reactive sites can not only improve the activity, selectivity, and durability for electrocatalytic NRR, but also deepen the understanding of the reaction mechanism. In this review, the roles of reactive sites in electrocatalytic NRR and the electrocatalytic NRR mechanism are introduced first. Then the typical strategies to construct and characterize atomic-level reactive sites are summarized. Next, the recent progress in rational design and development of atomic-level reactive sites for electrocatalytic NRR is summarized and discussed, with a focus on single-atoms, dual-atoms, metal clusters, vacancies, and dopants. Additionally, the rigorous protocols for electrocatalytic NRR are listed. Finally, the challenges and perspectives of atomic-level reactive sites in electrocatalytic NRR are proposed to develop more credible high-efficiency NRR electrocatalysts.