Heterostructure‐Derived Heterovalent Fe(OH)2/Fe Pair Sites: Tuning Adsorption of Intermediates and Enhancing Utilization of Atomic *H for Efficient Nitrate Reduction to Ammonia

Abstract Electrocatalytic nitrate reduction (NO3RR) to valued ammonia is an ideal supplementary route to the Haber–Bosch method and a strategy for the removal and utilization of nitrate pollutants. However, due to the fact that NO3RR goes through a complicated multi‐electron/proton transfer, catalysts with monovalent metal sites are difficult to tackle multitasking that it involves, leading to unsatisfactory nitrate conversion efficiency and ammonia selectivity. Herein, heterovalent Fe(OH) 2 /Fe pair sites supported onto carbon nanotubes (Fe(OH) 2 /Fe@CNTs) are presented via electrochemical reconstruction of CNTs‐supporting FeS/Fe 2 C heterostructure. Fe(OH) 2 /Fe@CNTs exhibits a high NH 3 yield rate of 0.67 mmol h −1 cm −2 with a FE of 95.1% at −0.4 V versus RHE, which is mainly attributed to the regulated electronic structure and cooperation of heterovalent iron pair sites. Meanwhile, the adsorption of nitrogen‐containing species is adjusted and the utilization of * H is enhanced. Moreover, a balanced content of Fe(OH) 2 and Fe creates “buffering effect” to maintain its activity and stability. Theoretical calculations combined with in situ FTIR and in situ Raman spectra reveal a novel multiple reaction pathway on heterovalent Fe(OH) 2 /Fe pair sites, entirely different from a single pathway on monovalent Fe or Fe(OH) 2 . Clearly, this study offers a creative strategy for the design of advanced catalysts with multivalent metal sites.