Recent advances in metal single-atom catalysts for ammonia electrosynthesis.

Electrochemical ammonia synthesis is a promising alternative to the Haber-Bosch process, offering significant potential for sustainable agricultural production and the development of portable, carbon-free energy carriers. The development of electrocatalytic systems is currently dependent on the exploration of electrocatalysts with high activity, selectivity, and stability. Metal single-atom catalysts (SACs) have become a new attractive frontier for ammonia electrosynthesis, owing to their maximized atom utilization, unsaturated atom coordination, and tunable electronic structure. In this review, we focused on different metal sites inside the single-atom catalysts and summarized recent advances in SACs for ammonia electrosynthesis. The properties of small nitrogenous substances (including N₂, NO, NO₂^-, and NO₃^-) are summarized. In addition, the SACs for different catalytic systems are reviewed, with a particular focus on the special and common grounds of metal atom sites. Finally, the perspectives and challenges of SACs for ammonia electrosynthesis are comprehensively discussed, aspiring to provide insights into the development of electrochemical ammonia synthesis.