Descriptor-guided atomic-scale engineering of single-atom catalysts for electrochemical nitrogen reduction

Electrochemical nitrogen reduction reaction (eNRR) offers a sustainable pathway for ammonia synthesis under ambient conditions; however, its practical implementation remains hindered by the inertness of the NN bond, limited N₂ activation, and the competing hydrogen evolution reaction (HER). Single-atom catalysts (SACs), comprising isolated metal atoms anchored on engineered supports, have emerged as a promising platform due to their maximum atomic utilization, well-defined active sites, and tunable electronic structures. In this review, we systematically summarize recent advances in atomic-scale engineering strategies-namely coordination engineering, heteroatom doping, defect engineering, and strain modulation-that govern the activity and selectivity of SACs for eNRR. These approaches collectively regulate the geometric and electronic environments of active centers, influencing charge redistribution, orbital hybridization, N₂ adsorption, and reaction energetics, while also enabling suppression of HER. Importantly, we highlight the growing role of descriptor-based design principles in establishing unified structure-activity relationships. By correlating geometric descriptors (e.g., coordination number, bond length, and local symmetry) and electronic descriptors (including d-band center, charge transfer, spin state, and adsorption-free energies of key intermediates) with catalytic performance, a predictive framework for rational SAC design is established. Furthermore, the importance of realistic theoretical modelling of the electrode-electrolyte interface is emphasized, as it provides deeper insight into potential-dependent mechanisms, interfacial effects, and dynamic evolution of active sites under operating conditions. Finally, key challenges-including catalyst stability, scaling limitations, HER competition, and synthesis scalability-are critically discussed, along with future directions integrating advanced synthesis, operando characterization, and data-driven modelling. This review provides comprehensive guidelines for the rational development of efficient, selective, and durable SACs toward practical electrochemical nitrogen fixation.