Efficient Nitrate Conversion to Ammonia on f-Block Single-Atom/Metal Oxide Heterostructure via Local Electron-Deficiency Modulation

Exploring single-atom catalysts (SACs) for the nitrate reduction reaction (NO₃^-; NitRR) to value-added ammonia (NH₃) offers a sustainable alternative to both the Haber-Bosch process and NO₃^--rich wastewater treatment. However, due to the insufficient electron deficiency and unfavorable electronic structure of SACs, resulting in poor NO₃^--adsorption, sluggish proton (H*) transfer kinetics, and preferred hydrogen evolution, their NO₃^--to-NH₃ selectivity and yield rate are far from satisfactory. Herein, a systematic theoretical prediction reveals that the local electron deficiency of an f-block Gd single atom (Gd_SA) can be significantly regulated upon coordination with oxygen-defect-rich NiO (Gd_SA-D-NiO₄₀₀) support. Thus, facilitating stronger NO₃^- adsorption via strong Gd_5d-O_2p orbital coupling and further improving the protonation kinetics of adsorption intermediates by rapid H* capture from water dissociation catalyzed by the adjacent oxygen vacancy site along with suppressed H* dimerization synergistically boosts the NH₃ selectivity/yield rate. Motivated by DFT prediction, we delicately stabilized electron-deficient (strongly electrophilic) Gd_SA on D-NiO₄₀₀ (∼84% strong electrophilic sites), which exhibited excellent alkaline NitRR activity (NH₃ Faradaic efficiency ∼97% and yield rate ∼628 μg/(mg_cat h)) along with superior structural stability, as revealed by in situ Raman spectroscopy, significantly outperforming weakly electrophilic Gd nanoparticles, defect-free Gd_SA-P-NiO₄₀₀, and reported state-of-the-art catalysts.