Creating Anionic Microenvironment Around Single‐Atom Fe Sites in Metal–Organic Frameworks for Enhanced Nitrate Electroreduction

The electrocatalytic nitrate reduction reaction (eNO₃RR) offers a sustainable strategy for both NO₃ ⁻ wastewater remediation and value-added NH₃ production. However, its application is hindered by sluggish reaction kinetics in neutral media due to the limited availability of protons. Herein, an anionic metal-organic framework (MOF), SU-102, is functionalized with atomically dispersed Fe sites to yield SU-102-Fe. This catalyst achieves a Faradaic efficiency (FE) of 96.9% and NH₃ production rate of 1.72 mg h⁻¹ mgcat ⁻¹ at -0.7 V versus RHE, far surpassing the commercial Fe₂O₃ and pristine SU-102. In situ characterizations reveal that the negatively charged Zr─O units in SU-102 create an anionic microenvironment around the Fe sites, which enriches K⁺•H₂O species derived from the interfacial hydrogen-bonding network. The facile dissociation of K⁺•H₂O improves local proton supply, facilitating NO₃ ⁻-to-NH₃ conversion and accounting for the superior eNO₃RR performance of SU-102-Fe.