When nitrogen reduction meets single-atom catalysts

Photocatalytic or electrocatalytic transformation of N₂-to-NH₃, serving as an alternative to the Haber-Bosch process that is energy- and capital-intensive, from abundant N₂, H₂O, solar energy, and clean and renewable electricity, offers great opportunities for sustainable agricultural production and portable carbon-free energy carrier. These new conversion technologies are highly dependent on the exploration of contributing photo/electrocatalysts, marking high activity, selectivity, and stability toward N₂ fixation. Single-atom catalysts (SACs) have emerged as a new attractive frontier in NH₃ photo/electrosynthesis, owing to their integrated merits of maximized atom utilization, unsaturated atom coordination, and tunable electronic structure. Herein, we provide an in-time summary of the recent advances in this dynamic research area. We start with a fundamental understanding of photo/electrocatalytic N₂ reduction, in terms of NH₃ quantification, and fundamental matrices being pursued. Followed on, we highlight and summarize synthesis strategies and analytical techniques for these SACs, with attention to elaborately diverse SACs supports. We further translate these mechanistic discussions by virtue of theoretical simulations, leveraging structure–property relationships in NH₃ photo/electrosynthesis. Finally, we also discuss the bigger picture of photo/electrocatalytic NH₃ production, among which N₂ reduction challenges are assessed, shedding some light on the state-of-the-art SACs as photo/electrocatalysts for NH₃ production through N₂ fixation.