Title : Redox engineering of Fe-MOF-74 for selective electrochemical NO-to-NH₃ conversion under dilute NO conditions
Abstract:
The electrochemical reduction of nitric oxide (NO) to ammonia (NH?) offers a promising strategy for both environmental remediation and sustainable chemical synthesis. However, selective NO conversion under dilute flue-gas-relevant conditions remains challenging because of the low availability of gaseous NO and the competing hydrogen evolution reaction (HER). Here, we report a redox-engineered iron-based metal–organic framework, Fe-MOF-74, as a highly selective electrocatalyst for NO-to-NH? conversion under dilute NO feed conditions. By systematically tuning the oxidation state and local coordination environment of the Fe centers, we establish a direct relationship between the electronic structure of the active sites and the adsorption and activation of dilute NO molecules. Synchrotron X-ray absorption spectroscopy (XAS) and Mössbauer spectroscopy reveal that modulation of the Fe(II)/Fe(III) redox states alters the local electronic environment of the Fe sites, promoting NO activation while suppressing the competing HER. This optimized electronic structure facilitates the sequential proton-coupled electron-transfer steps required for NH? formation. Electrochemical measurements demonstrate that the redox-tuned Fe-MOF-74 maintains high NH? Faradaic efficiency and productivity even under highly dilute NO concentrations representative of flue-gas conditions. These findings demonstrate the importance of controlling the redox state and coordination environment of metal centers in MOF-based electrocatalysts and provide mechanistic insights into the structure–activity relationship governing dilute NO reduction. This work offers a catalyst-design strategy for developing selective electrocatalysts for sustainable NO valorization and gas-phase nitrogen upcycling.
