Spin polarized Fe1−Ti pairs for highly efficient electroreduction nitrate to ammonia

Electrochemical nitrate reduction to ammonia offers an attractive solution to environmental sustainability and clean energy production but suffers from the sluggish *NO hydrogenation with the spin-state transitions. Herein, we report that the manipulation of oxygen vacancies can contrive spin-polarized Fe₁-Ti pairs on monolithic titanium electrode that exhibits an attractive NH₃ yield rate of 272,000 μg h^-1 mg_Fe^-1 and a high NH₃ Faradic efficiency of 95.2% at -0.4 V vs. RHE, far superior to the counterpart with spin-depressed Fe₁-Ti pairs (51000 μg h^-1 mg_Fe^-1) and the mostly reported electrocatalysts. The unpaired spin electrons of Fe and Ti atoms can effectively interact with the key intermediates, facilitating the *NO hydrogenation. Coupling a flow-through electrolyzer with a membrane-based NH₃ recovery unit, the simultaneous nitrate reduction and NH₃ recovery was realized. This work offers a pioneering strategy for manipulating spin polarization of electrocatalysts within pair sites for nitrate wastewater treatment.