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 (NO 3 - ; NitRR) to value-added ammonia (NH 3 ) offers a sustainable alternative to both the Haber-Bosch process and NO 3 - -rich wastewater treatment. However, due to the insufficient electron deficiency and unfavorable electronic structure of SACs, resulting in poor NO 3 - -adsorption, sluggish proton (H*) transfer kinetics, and preferred hydrogen evolution, their NO 3 - -to-NH 3 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-NiO 400 ) support. Thus, facilitating stronger NO 3 - 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 NH 3 selectivity/yield rate. Motivated by DFT prediction, we delicately stabilized electron-deficient (strongly electrophilic) Gd SA on D-NiO 400 (∼84% strong electrophilic sites), which exhibited excellent alkaline NitRR activity (NH 3 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-NiO 400 , and reported state-of-the-art catalysts.