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

Abstract

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 (similar to 84% strong electrophilic sites), which exhibited excellent alkaline NitRR activity (NH3 Faradaic efficiency similar to 97% and yield rate similar to 628 mu g/(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.