Reconstructed low-valent Fe single-atom sites on deficient TiO 2 enable electrocatalytic nitrate reduction to ammonia

Abstract Electrochemical nitrate (NO3−) reduction reaction (NO3RR) offers a promising route for NO3− remediation and sustainable ammonia (NH3) synthesis, yet its efficiency is often constrained by the hydrogenation of nitrogen-containing intermediates. Herein, we report Fe single atoms anchored on oxygen-vacancy-rich TiO2 nanosheet assemblies (FeSA-TiO2-Ov) for efficient NO3− to NH3 conversion. The FeSA-TiO2-Ov catalyst achieves a high NH3 yield rate of 16.6 mg·h−1·cm−2 at −0.5 V versus reversible hydrogen electrode (vs. RHE), accompanied by a maximum Faradaic efficiency of 92% and excellent durability over 40 h. Operando X-ray absorption fine structure (XAFS) spectroscopy reveals a gradual decrease in Fe valence and contraction of the Fe–O coordination shell, confirming the formation of reconstructed low-valent Fe single-atom active sites during NO3RR. Theoretical calculations and spectroscopic analysis further indicate that Fe sites are effective for *NO hydrogenation to the *NOH intermediate, thereby promoting the efficient formation of NH3. These findings identify the reconstructed low-valent Fe single atoms as the active sites for selective electrosynthesis of NH3, providing a mechanistic framework for designing single-atom catalysts applicable to multistep electrocatalytic reduction reactions.