Nano‐Single‐Atom Heterointerface Engineering for pH‐Universal Electrochemical Nitrate Reduction to Ammonia

Abstract Nano‐single‐atom‐catalysts have the potential to combine the respective advantages of both nano‐catalysts and single‐atom‐catalysts and thus exhibit enhanced performance. Generally, the separation of active sites in space limits the interaction between single atoms and nanoparticles. Heterointerface engineering has the potential to break this limitation. Regretfully, studies on the interface effect between single atoms and nanoparticles are rarely reported. Herein, an unprecedented nano‐single‐atom heterointerface composed of Fe single‐atoms and carbon‐shell‐coated FeP nanoparticles (Fe SAC/FeP@C) is demonstrated as an efficient electrocatalyst for the nitrate reduction process from alkaline to acidic. Compared with typical nano‐single‐atom‐catalysts (Fe SAC/FePO₄) and single‐atom‐catalysts (Fe SAC), the constructed Fe SAC/FeP@C heterostructure exhibits dramatically enhanced nitrate‐to‐ammonia performance. Especially in acidic media, the maxmium Faradaic efficiency of ammonia (NH₃) can reach 95.6 ± 0.5%, with a maximum NH₃ yield of 36.2 ± 3.1 mg h⁻¹ mg_cat⁻¹ (pH = 1.2), which is considerably higher than previously reported. Density functional theory calculations and in situ spectroscopic investigations indicate that the unique charge redistribution at the interface, together with the optimized electronic structure of Fe single‐atoms, strengthens intermediate adsorption and catalytic activity. This work provides a feasible strategy for designing nano‐single‐atom‐catalysts with unique heterointerfaces, as well as valuable insights into nitrate conversion under environmentally relevant wastewater conditions.